- Open Access
HIV-tat alters Connexin43 expression and trafficking in human astrocytes: role in NeuroAIDS
© Berman et al. 2016
Received: 1 October 2015
Accepted: 14 February 2016
Published: 2 March 2016
HIV-associated neurocognitive disorders (HAND) are a major complication in at least half of the infected population despite effective antiretroviral treatment and immune reconstitution. HIV-associated CNS damage is not correlated with active viral replication but instead is associated with mechanisms that regulate inflammation and neuronal compromise. Our data indicate that one of these mechanisms is mediated by gap junction channels and/or hemichannels. Normally, gap junction channels shutdown under inflammatory conditions, including viral diseases. However, HIV infection upregulates Connexin43 (Cx43) expression and maintains gap junctional communication by unknown mechanism(s).
Human primary astrocytes were exposed to several HIV proteins as well as to HIV, and expression and function of Connexin43- and Connexin30-containing channels were determined by western blot, immunofluorescence, microinjection of a fluorescent tracer and chromatin immunoprecipitation (ChIP).
Here, we demonstrate that HIV infection increases Cx43 expression in vivo. HIV-tat, the transactivator of the virus, and no other HIV proteins tested, increases Cx43 expression and maintains functional gap junctional communication in human astrocytes. Cx43 upregulation is mediated by binding of the HIV-tat protein to the Cx43 promoter, but not to the Cx30 promoter, resulting in increased Cx43 messenger RNA (mRNA) and protein as well as gap junctional communication.
We propose that HIV-tat contributes to the spread of intracellular toxic signals generated in a few HIV-infected cells into surrounding uninfected cells by upregulating gap junctional communication. In the current antiretroviral era, where HIV replication is often completely suppressed, viral factors such as HIV-tat are still produced and released from infected cells. Thus, blocking the effects of HIV-tat could result in new strategies to reduce the damaging consequences of HIV infection of the CNS.
HIV enters the CNS early after infection, and CNS viral persistence results in many neurological abnormalities [1, 2]. As the prevalence of HIV-associated neurocognitive disorders (HAND) increases [2, 3], understanding the mechanisms mediating the pathogenesis of HAND becomes even more critical. Currently, there is no correlation between the low to undetectable levels of HIV replication and extensive CNS damage. Therefore, several groups suggested that this damage is due to amplification systems used by the virus to increase HIV-associated inflammation. We propose that connexin (Cx)-containing gap junctions (GJ) and hemichannels (HC) are important in the amplification of this disease process.
Gap junctions are aggregates of channels connecting the cytoplasmic compartments of the coupled cells and provide direct continuity between the cells allowing electrical and metabolic coordination [4, 5]. A GJ channel is formed by the docking of two hemichannels (one contributed by each of the joined cells), and each hemichannel is composed of six protein subunits termed connexins (Cx). Recent evidence indicates that hemichannels composed of Cx in non-junctional membranes can open to the extracellular space under appropriate conditions and allow diffusional exchange between the cytoplasmic compartment and the extracellular environment, including highly inflammatory factors such as ATP, glutamate, and prostaglandins [4, 5].
Astrocytes are the most abundant cell type in the CNS and are highly coupled by gap junctions containing Cx43 and Cx30 to coordinate metabolic and electric events , and only recently, there is increasing evidence of their significance in HIV infection. Despite their low viral replication and percentage of HIV-infected astrocytes present in vivo and in vitro (5 to 19 %), significant changes in astrocyte gene expression , apoptosis [7–10], glutamate metabolism, and blood brain barrier (BBB) [7, 8] have been reported, suggesting that these cells play a key role in NeuroAIDS.
Our laboratories demonstrated that despite low replication and numbers of HIV-infected astrocytes, Cx containing channels, including gap junctions and hemichannels, allow toxins from these few HIV-infected astrocytes to reach neighboring uninfected CNS cells [4, 7, 8, 11]. In our studies, it was surprising that connexin channels in human astrocytes are maintained or increased in response to HIV infection. Generally, Cx expression and gap junctional communication are decreased under inflammatory conditions, including viral infections [4, 12]. However, HIV infection of astrocytes results in opening of hemichannels, increased Cx43 expression, and maintenance of gap junctional communication [4, 7, 8, 11]. In this report, we demonstrate that expression of Cx43, but not of Cx30, is upregulated in HIV-infected conditions, especially in tissues obtained from HIV-infected individuals with cognitive impairment. In addition, we demonstrate that HIV-tat protein binds to the Cx43 promoter, resulting in an increase in Cx43 mRNA and protein expression as well as in the maintenance of gap junctional communication. Our results of the maintenance of Cx43 expression may explain how few HIV-infected astrocytes spread intracellular toxic signals into surrounding uninfected cells.
DMEM, fetal bovine serum (FBS), penicillin/streptomycin (P/S), and trypsin-EDTA were from Invitrogen (Grand Island, NY). Monoclonal antibody to GFAP, FITC or Cy3- conjugated anti-rabbit IgG, and Cy3 or FITC-coupled anti-mouse IgG antibodies were from Sigma (St. Louis, MO). Purified mouse IgG2B and IgG1 myeloma proteins were from Cappel Pharmaceuticals, Inc. Lipofectamine 2000; anti-connexin43 antibody; anti-connexin30 antibody; and secondary antibodies anti-mouse, anti-rabbit, and anti-goat immunoglobulins conjugated to Alexa-533, Alexa-633, and Alexa-588 were from Life Technologies (Eugene, OR). Small interfering RNA (siRNA) for Cx30 and controls were from Santa Cruz Biotechnology (Santa Cruz, CA). HIV recombinant proteins, vif, nef, rev, gag (p55, p24, and p7), polymerase, and gp120 as well as HIVADA and HIVJR-CSF were from the NIH repository (Germantown, MD). HIV-tat protein was purchased from the University of Kentucky or was a gift from Dr. Avindra Nath (NINDS, NIH, MD). We selected concentrations from 1 to 300 ng/ml due to the effects on neuronal toxicity (100 ng/ml induces neuronal apoptosis in 50–80 % of the cells and lower concentrations induce minimal apoptosis, 10–20 % [13, 14]). In addition, HIV-tat induced chemotaxis was also maximal at 100 ng/ml . Concentrations below 100 ng/ml only induced minimal microglia migration. Thus, the concentrations selected (1 to 300 ng/ml) are appropriate in different models.
Brain tissue sections
Human brain tissue sections (10 to 20 μm) were obtained from the National NeuroAIDS Tissue Consortium (NNTC). This consortium is a NIH-funded (U24MH100925) source to explore the devastating consequences of HIV infection (www.nntc.org).
Human astrocyte cultures and HIV infection
Cortical human fetal tissue was obtained as part of a research protocol approved by the Albert Einstein College of Medicine and Rutgers University. The astrocyte cultures were prepared as previously described and were obtained from either gender [7, 16]. Confluent cultures of human astrocytes were infected by incubation with viral stocks (20–50 ng p24/ml/1 × 106 cells), HIVADA or HIVJR-CSF, using a previously described protocol [7, 8, 13].
Three unique 29mer siRNA duplexes to human Cx30 were designed and obtained from Origene (Rockville, MD). siRNA (10 nM) transfection was performed with Oligofectamine (Invitrogen) according to the Origene application guide for Trilencer-29 siRNA. Minimal cell death was detected after transfection. Experiments were performed 2 days post transfection.
Astrocytes were grown on coverslips, fixed, and permeabilized in 70 % ethanol for 20 min at −20 °C. Cells were incubated in blocking solution for 30 min at room temperature and then in diluted primary antibody (anti-HIV-p24, anti-Cx43, anti-Cx30, and anti-GFAP; 1:50, 1:2000, 1:300, and 1:800, respectively) overnight at 4 °C. Cells were washed several times with PBS at room temperature and incubated with the appropriate secondary antibodies for at least 3 h at room temperature followed by another wash in PBS for 1 h. Cells were examined by confocal microscopy using an A1 confocal microscope (Nikon, Japan). Antibody specificity was confirmed by replacing the primary antibody with a non-specific myeloma protein of the same isotype or non-immune serum as we previously described [17, 18].
Immunofluorescent and confocal microscopy analysis of human brain tissue samples
Postmortem human brain tissue sections from uninfected controls (four cases) and HIV-infected individuals with HIV encephalitis (HIVE, four cases) and minor cognitive disease (five cases) were analyzed by four color immunohistochemical staining for DAPI (nuclei staining), HIV-p24 (HIV viral protein), Cx43 or Cx30, and GFAP (an astrocyte marker). Sections of 10 μm were deparaffinized, underwent antigen retrieval, and blocked (5 mM EDTA, 1 % fish gelatin, 1 % essentially Ig-free BSA, 2 % human serum, and 2 % horse serum) for 60 min at room temperature and then incubated with anti-HIV-p24 (HIV viral protein), Cxs, and GFAP (an astrocyte marker) overnight at 4 °C. The sections were washed with PBS, incubated with secondary antibodies for 1 h at room temperature, followed by serial washes in PBS for 1 h. The samples were then mounted using Prolong Gold anti-fade reagent (Invitrogen) and examined by confocal microscopy. Specificity was confirmed by replacing the primary antibody with the appropriate isotype-matched control reagent, anti-IgG2A, or the IgG fraction of normal rabbit serum (Santa Cruz, Biotechnology).
Relative levels of Cx43, Cx30, and tubulin were determined by immunoblot as described [13, 19]. Astrocyte cultures were treated with HIV- tat or vehicle and harvested in Tris buffer, 10 mM pH 7.4, containing protease and phosphatase inhibitors (20 mM; pyrophosphate, 20 mM; NaF, 100 mM; NaVO3, 200 μM; leupeptin, 500 μg/ml; aprotinin, 40 μg/ml; soybean trypsin inhibitor, 2 mg/ml; benzamidine, 1 mg/ml; ω-amino caproic acid, 1 mg/ml; PMSF, 3 mM; and EDTA, 20 mM) [13, 19]. Cells were lysed, and the protein content of each cell lysate was determined using Bradford’s method  (Bio-Rad labs, Hercules, CA). Samples containing 20 μg of protein were used to analyze Cx43, Cx30, and tubulin. Proteins were separated in 7.5 % SDS-PAGE and electrophoretically transferred to nitrocellulose, which was then incubated sequentially with blocking solution (5 % non-fat milk in Tris-buffered saline); affinity-purified rabbit polyclonal antibodies prepared against Cx43, Cx30, and tubulin (1:2000, 1:500, and 1:2000, respectively); and anti-rabbit IgG conjugated to HRP. Antigen-antibody complexes were detected by ECL (Perkin Elmer, Boston, MA) and the resulting immunoblot signals were scanned, and densitometric analysis was performed using NIH-image software. All results were normalized to the values obtained for control conditions.
To evaluate the function of gap junction channels, the intercellular transfer of Lucifer Yellow (LY) (5 % w/v in 150 mM LiCl) was evaluated by microinjecting the dye into a single cell and evaluating the diffusion of the dye into neighboring cells, as previously described . Cells were scored as coupled if dye transfer occurred to one or more adjacent cells. Dye transfer was evaluated using a fully motorized Zeiss Z1 microscope. Four independent experiments were performed in which a minimum of 20 cells were microinjected per experiment. The incidence and index of dye coupling was scored as the percentage of injections that resulted in dye transfer and the numbers of cells coupled to a single microinjected cell.
Primary human astrocytes were transfected with pcDNA3.1+/tat101-flag (NIH repository, 10453) with Lipofectamine 2000. Twenty-four hours post transfection, chromatin immunoprecipitation (ChIP) analysis was performed for Cx43 and Cx30. In brief, cells were fixed and cross-linked using 1 % formaldehyde and washed in PBS, as we described with minor modifications . Cells were homogenized, sonicated until 500-bp fragments were obtained using 20 pulses of 30 s on and 30 s off in a Microtip (Misonix, Inc, Microson XL-2000). Samples were pre-cleared with protein A/G and immunoprecipitated using anti-FLAG antibodies (Sigma). Specific binding of HIV-tat to Cx43 and Cx30 promoters was analyzed by qRT-PCR using a StepOnePlus Real Time PCR system (Life Technologies) and absolute blue QPCR SYBR low Rox Mix (Life Technologies). Single product amplification was confirmed by melting curve analysis, and primer efficacy was near or close to 100 % in all experiments. The human Cx43 promoter forward primer 5′-CCT CCT CCC AGT TGA GTC AG-3′ and reverse primer 5′-ACG CCA AGT GAT TGA ACT CC-3′ were described previously . Human Cx30 promoter was analyzed using the following primers: forward 5′-TCC TGC ACT CCT TGC TCC TCA-3′ and reverse 5′-TCC CAC CTG CTG CGC CTT T .
HIV-p24 concentrations in the medium of uninfected and HIV-infected cultures were determined by ELISA using a commercial kit from Perkin Elmer (Boston, MA).
Mean differences were tested by non-parametric Kruskal-Wallis analysis or student’s t test. If a significant F value was obtained, means were compared with Bonferroni-Dunn multiple comparison test. A value of p < 0.05 was considered significant.
Cx43, but not Cx30, is upregulated in human brain tissue sections obtained from subjects with HIV mild cognitive disease and encephalitis
HIV-tat protein, but not other HIV proteins, increases Cx43 expression
Our previous data and the data described above indicate that HIV-infected astrocytes and surrounding cells have increased expression of Cx43 and gap junctions remain functional during HIV infection of the CNS [7, 8] and that HIV infection resulted in the opening of Cx43-containing hemichannels . These results indicate that despite HIV infection and associated inflammation that normally result in gap junction closure, gap junctions and hemichannels are present and active. In other inflammatory and viral diseases, these channels are shut down [4, 5]. Thus, HIV infection is different. However, the mechanism(s) by which HIV regulates Cx expression in human astrocytes were unknown.
Expression of Cx43 by astrocytes after different HIV treatments
Cx43 expression in astrocytes (percentage of control, n = 5)
HIVADA (20 ng/ml)
HIVJR-CSF (20 ng/ml)
Treatment (recombinant proteins)
Vif (1, 100, and 300 ng/ml)
Gag (p55, p24, or p7: 1, 100, and 300 ng/ml)
Rev (1, 100, and 250 ng/ml)
Nef (1, 100, and 250 ng/ml)
Gp120 (1, 50, and 100 nM)
−8.6 ± 1.3*
−5.4 ± 3.2*
−4.1 ± 1.2*
−3.1 ± 0.5*
HIV-tat1–72 (1, 100, and 300 ng/ml)
45.1 ± 12.3*
21.3 ± 8*
21.1 ± 2.2*
25.1 ± 2.5*
IL-1β (10 ng/ml)
−10.2 ± 5.2*
−16 ± 6.89*
−61.3 ± 11*
−69.9 ± 12.6*
Expression of Cx30 on astrocytes after different HIV treatments
Cx30 expression in astrocytes (percentage of control, n = 3)
HIVADA (20 ng/ml)
−12.3 ± 9.9*
−22.5 ± 8.9*
−32 ± 9.88*
−38.9 ± 7.9*
HIVJR-CSF (20 ng/ml)
−28.7 ± 6.8*
−32.7 ± 11*
−49.8 ± 14.6*
−65.5 ± 21.2*
Treatment (recombinant proteins)
Vif (1, 100, and 300 ng/ml)
−3.8 ± 1.06*
−5.99 ± 2.3*
−8.88 ± 4.5 *
−8.98 ± 5.6*
Gag (p55, p24, or p7: 1, 100, and 300 ng/ml)
Rev (1, 100, and 250 ng/ml)
Nef (1, 100, and 250 ng/ml)
−5.3 ± 3.2*
−8.6 ± 3.43*
−12.7 ± 6.6*
−14.9 ± 7.45*
Gp120 (1, 50, and 100 nM)
−3.44 ± 2.1*
−5.6 ± 5.4*
−8.88 ± 4.3*
−9.15 ± 3.3*
HIV-tat1–72 (1, 100, and 300 ng/ml)
−9.02 ± 3.3*
−10.5 ± 5.4*
−17.5 ± 3.9*
−28.1 ± 11.8*
IL-1β (10 ng/ml)
−21.7 ± 8.9*
−36.54 ± 9*
−51.3 ± 9.3*
−52.3 ± 21.5*
Furthermore, Cx43 protein expression was not altered by any concentration of recombinant vif, gag, rev, or nef at any time point examined (Table 1). However, all gp120 concentrations tested decreased Cx43 expression by 3 to 9 % (p < 0.005, n =4), suggesting that this HIV protein is not involved in maintaining or increasing Cx43 expression (Table 1). In contrast, exon 1 (HIV-tat1–72) or both exons (HIV-tat1–101; data not shown) of HIV-tat resulted in upregulation of Cx43 protein expression at all concentrations and time points tested (Table 1).
In contrast, HIV infection (ADA and JR-CSF) and the recombinant proteins vif, nef, and gp120 decreased Cx30 protein expression at all concentrations tested (Table 2). Gag and Rev did not alter Cx30 protein expression (Table 2). HIV-tat resulted in decreased expression of Cx30 at all three concentrations and times tested (Table 2). These results indicate that HIV-tat contributes to the maintained or increased expression of Cx43 but contributes to the reduction in Cx30 expression.
HIV-tat upregulates Cx43 mRNA and protein as well as increases gap junctional communication
To determine the mechanism(s) by which HIV-tat increased Cx43 protein expression, we evaluated Cx43 mRNA and protein, as well as gap junctional communication after HIV-tat treatment. Human astrocyte cultures were treated with 1, 100, or 300 ng/ml of HIV-tat for 6, 12, 24, and 48 h, and cells were analyzed by confocal microscopy, qRT-PCR, western blotting, and dye coupling (Fig. 2, only 100 ng/ml of HIV-tat is shown).
Cx43, GFAP, and nuclear staining, and subsequent analysis by confocal microscopy, demonstrated that Cx43 is mostly located in the plasma membrane and the cytoplasm in control conditions as expected (Fig. 2a, control). When cells were treated with HIV-tat, Cx43 staining in the membrane and cytoplasm was increased in all astrocytes (Fig. 2a, HIV-tat, 24 h). qRT-PCR analysis for Cx43 and GAPDH mRNA demonstrated that HIV-tat upregulates Cx43 mRNA up to ~sixfold as compared to untreated cells (Fig. 2b, *p ≤ 0.002 at all-time points analyzed). Western blot analysis of these samples indicated that HIV-tat treatment increased Cx43 protein 6 to 48 h post treatment (Fig. 2c at all-time points analyzed, p ≤ 2.3 × 10−5). Tubulin was used as a loading control (Fig. 2c, tub).
To examine the function of these channels, dye coupling was performed. In control conditions, astrocytes were 100 % coupled to other surrounding astrocytes (data not shown) with an average of 10 ± 2.6 cells coupled for each cell microinjected with LY (Fig. 2d, dye coupling index). HIV-tat treatment of human astrocytes increased the numbers of coupled cells up to 27.3 ± 4.76 cells per microinjection (Fig. 2d, *p < 0.003), suggesting that toxic signals generated in a few HIV-infected astrocytes could reach longer distances by a HIV-tat-dependent mechanism.
Furthermore, HIV-tat effects on Cx43 expression and gap junctional communication were specific to human cells, because treatment of mouse astrocytes with HIV-tat (100 ng/ml) for 6 to 72 h did not alter Cx43 expression or gap junctional communication, suggesting that the effect is species specific, as is HIV infectivity (data not shown).
HIV-tat protein downregulates Cx30 expression, while Cx30 does not contribute to the increased coupling index observed after HIV-tat treatment
HIV-tat binds to the Cx43 promoter, but not to the Cx30 promoter
The main function of HIV-tat protein in the HIV cell cycle is to enhance and stabilize Pol II transcription of the viral DNA. HIV-tat binds to the RNA stem-loop structure, the trans-activating response (TAR) element, found at the 5′ ends of nascent HIV transcripts. HIV-tat’s binding to TAR alters the formation of the transcription complex and recruits the transcription factor P-TEFb of CDK9 and cyclin T1, to increase the production of full length viral RNA [28, 29]. However, it was unknown whether HIV-tat binds and affects Cx43 promoter activity.
In this report, we demonstrate that HIV-tat, the transactivator of the virus, binds to the Cx43 promoter and increases Cx43 mRNA, protein, and gap junctional communication. Thus, HIV-tat not only regulates HIV transcription but also regulates an important host gene within the CNS. Our published data demonstrate that the maintenance or increase of Cx43 and gap junctional communication as well as increased hemichannel opening are essential to mediate bystander apoptosis between the few infected astrocytes (4.7 ± 2.8 % in vitro and 8.2 ± 3.9 % in vivo using an SIV model) and neighboring uninfected cells such as uninfected astrocytes, neurons, and brain endothelial cells [5, 7, 8, 25]. Our previous studies also demonstrated that maintenance of gap junctional communication by HIV infection enables intracellular toxic signals, including cytochrome C-related signals (cytochrome C cannot cross gap junctions due to its size), IP3, and calcium generated in a few HIV-infected astrocytes to spread to uninfected communicated cells resulting in amplification of apoptosis and inflammation. All of these changes are independent of active HIV replication. Thus, bystander damage is associated with infection, but not with replication, as HIV-tat is produced by HIV-infected cells even in the presence of anti-retrovirals [30, 31]. This may be an important mechanism mediating HIV CNS damage despite inefficient HIV-infected cells or replication.
Our data reflect the current status of the majority of people infected with HIV, where HIV replication is minimal due to successful antiretroviral treatment. However, despite low replication and normal CD4 counts, 50–70 % of the HIV-infected population shows some signs of cognitive impairment [32, 33]. Thus, it is not the virus mediating these effects; it is more likely that these are amplification systems altered by viral factors that are not impacted by antiretroviral treatment. Currently, antiretroviral treatments have no effect on HIV-tat production. Thus, this protein is produced and secreted independently of effective viral replication , suggesting that the effects observed in HIV-infected astrocytes could be present in HIV-infected individuals regardless of successful combination antiretroviral therapy (cART). In addition to the effects of HIV-tat on gap junctional communication, this HIV protein is also directly neurotoxic, capable of triggering inflammation and altering several synaptic components [13, 34, 35].
Our data and that of others have demonstrated a key role of astrocytes in the pathogenesis of NeuroAIDS by mechanisms that involve gap junctional communication, hemichannels, and Wnt pathways [11, 25, 36–39]. Thus, we propose that HIV-tat upregulates Cx-containing channels, including gap junctions and hemichannels, to spread toxic signals into neighboring cells by increasing the radius of diffusion of intracellular factors through gap junctions.
Normally, gap junctions are master regulators of electrical and metabolic coordination in most tissues including the CNS. It has recently become evident that connexin-containing channels, gap junctions and hemichannels, are also key regulators of learning and memory, long-term potentiation, and depression; the ratio of NR2a/NR2b; and electrical oscillations [40–45]. Thus, any changes in gap junctional communication or Cx expression will affect CNS function, as observed in HIV-infected individuals. These channels in parenchymal cells are shut down in response to inflammatory stimuli such as cytokines, chemokines, and pathogens [4, 5, 46]. However, HIV infection of astrocytes has a different effect, in that connexin-containing channels are maintained or increased, resulting in bystander apoptosis of uninfected cells. In agreement, some reports indicate that functional gap junction channels may help to amplify ischemic damage by enhancing the propagation of pro-apoptotic death signals between dying and healthy cells . Additionally, α-particle-irradiated cells also transmit pro-apoptotic signals through gap junctions to non-irradiated cells . These results suggest that gap junction channels can be used to spread damage into healthy areas.
Direct binding of HIV-tat to the Cx43 promoter was unexpected. The promoters for Cxs and long-term repeats (LTR) of HIV are very different and share the use of few transcription factors. The human Cx43 promoter contains several putative transcription factor binding sites including AP-1, AP-2, cAMP response elements, Ets, specificity protein-1 consensus sites, several sequences resembling half the palindromic estrogen response elements and progesterone response elements, and an activator and a repressor site that have been functionally characterized in the mouse gene [23, 49, 50]. There are no current elements shared by the virus and the Cx43 promoter that enable binding of Pol II in similar sites. HIV transcription requires the transcription factors TFIID, SP1, NF-kB, NFAT, and AP-1, and upstream also contains USF, Ets, and LEF-1 binding sites . Interestingly, we did not observe that HIV-tat increased Cx43 expression in mouse astrocytes, suggesting that HIV-tat effects are human DNA specific, similar to HIV infection. This may be due to the expression of cyclin T1, a human-specific protein. To characterize these differences, further studies are required to identify the areas of binding of Pol II to the Cx43 promoter, transcription factors, and how HIV-tat regulates these interactions.
Furthermore, HIV-tat binding to the Cx43 promoter was specific, because no binding was detected to the Cx30 promoter. Currently, there are few reports describing the sequences and binding sites in this promoter. It is known that Cx30 transcription can start in different exons, for example, in the epidermis, transcription begins in exon 1, but in the CNS, it starts in exon 3. In the promoter region of the Cx30 human gene, upstream of exon 1, a TATA motif, several potential binding sites for sp1, and a consensus sequence for early growth response gene products (Egr)-binding are present . However, any similarities or differences in the promoter need further description to identify the differences in HIV-tat sensitivity.
Our results suggest that blocking secretion or production of HIV-tat within the CNS or reducing gap junctional communication to physiological levels is a novel potential therapeutic approach to reduce the ongoing CNS compromise observed in a large population of HIV-infected individuals.
We thank the Fetal Tissue Repository at the Albert Einstein College of Medicine and the National NeuroAIDS Tissue Consortium (NNTC). This work was supported by the National Institutes of Health grants MH075679, MH102113, MH090958 (to J.W.B. and L.C.), and MH096625 (to E.A.E.).
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- Jernigan TL, Archibald SL, Fennema-Notestine C, Taylor MJ, Theilmann RJ, Julaton MD, et al. Clinical factors related to brain structure in HIV: the CHARTER study. J Neurovirol. 2011;17:248–57.View ArticlePubMedPubMed CentralGoogle Scholar
- Heaton RK, Franklin DR, Ellis RJ, McCutchan JA, Letendre SL, Leblanc S, et al. HIV-associated neurocognitive disorders before and during the era of combination antiretroviral therapy: differences in rates, nature, and predictors. J Neurovirol. 2011;17:3–16.View ArticlePubMedPubMed CentralGoogle Scholar
- Letendre S. Central nervous system complications in HIV disease: HIV-associated neurocognitive disorder. Top Antiviral Med. 2011;19:137–42.Google Scholar
- Eugenin EA. Role of Connexin/Pannexin containing channels in infectious diseases. FEBS Lett. 2014;588:1389–95.View ArticlePubMedPubMed CentralGoogle Scholar
- Eugenin EA, Basilio D, Saez JC, Orellana JA, Raine CS, Bukauskas F, et al. The role of gap junction channels during physiologic and pathologic conditions of the human central nervous system. J Neuroimmune Pharmacol. 2012;7(3):499–518.View ArticlePubMedPubMed CentralGoogle Scholar
- Wang Z, Trillo-Pazos G, Kim SY, Canki M, Morgello S, Sharer LR, et al. Effects of human immunodeficiency virus type 1 on astrocyte gene expression and function: potential role in neuropathogenesis. J Neurovirol. 2004;10 Suppl 1:25–32.View ArticlePubMedGoogle Scholar
- Eugenin EA, Clements JE, Zink MC, Berman JW. Human immunodeficiency virus infection of human astrocytes disrupts blood-brain barrier integrity by a gap junction-dependent mechanism. J Neurosci. 2011;31:9456–65.View ArticlePubMedPubMed CentralGoogle Scholar
- Eugenin EA, Berman JW. Gap junctions mediate human immunodeficiency virus-bystander killing in astrocytes. J Neurosci. 2007;27:12844–50.View ArticlePubMedPubMed CentralGoogle Scholar
- Thompson KA, McArthur JC, Wesselingh SL. Correlation between neurological progression and astrocyte apoptosis in HIV-associated dementia. Ann Neurol. 2001;49:745–52.View ArticlePubMedGoogle Scholar
- Ohagen A, Ghosh S, He J, Huang K, Chen Y, Yuan M, et al. Apoptosis induced by infection of primary brain cultures with diverse human immunodeficiency virus type 1 isolates: evidence for a role of the envelope. J Virol. 1999;73:897–906.PubMedPubMed CentralGoogle Scholar
- Orellana JA, Saez JC, Bennett MV, Berman JW, Morgello S, Eugenin EA. HIV increases the release of dickkopf-1 protein from human astrocytes by a Cx43 hemichannel-dependent mechanism. J Neurochem. 2014;128:752–63.View ArticlePubMedPubMed CentralGoogle Scholar
- Rouach N, Avignone E, Meme W, Koulakoff A, Venance L, Blomstrand F, et al. Gap junctions and connexin expression in the normal and pathological central nervous system. Biol Cell. 2002;94:457–75.View ArticlePubMedGoogle Scholar
- Eugenin EA, D'Aversa TG, Lopez L, Calderon TM, Berman JW. MCP-1 (CCL2) protects human neurons and astrocytes from NMDA or HIV-tat-induced apoptosis. J Neurochem. 2003;85:1299–311.View ArticlePubMedGoogle Scholar
- Eugenin EA, King JE, Nath A, Calderon TM, Zukin RS, Bennett MV, et al. HIV-tat induces formation of an LRP-PSD-95- NMDAR-nNOS complex that promotes apoptosis in neurons and astrocytes. Proc Natl Acad Sci U S A. 2007;104:3438–43.View ArticlePubMedPubMed CentralGoogle Scholar
- Eugenin EA, Dyer G, Calderon TM, Berman JW. HIV-1 tat protein induces a migratory phenotype in human fetal microglia by a CCL2 (MCP-1)-dependent mechanism: possible role in NeuroAIDS. Glia. 2005;49:501–10.View ArticlePubMedPubMed CentralGoogle Scholar
- Eugenin EA, Berman JW. Chemokine-dependent mechanisms of leukocyte trafficking across a model of the blood-brain barrier. Methods. 2003;29:351–61.View ArticlePubMedGoogle Scholar
- Subbian S, Eugenin E, Kaplan G. Detection of Mycobacterium tuberculosis in latently infected lungs by immunohistochemistry and confocal microscopy. J Med Microbiol. 2014;63:1432–5.View ArticlePubMedPubMed CentralGoogle Scholar
- Rella CE, Ruel N, Eugenin EA. Development of imaging techniques to study the pathogenesis of biosafety level 2/3 infectious agents. Pathog Dis. 2014;72(3):167–73.PubMedPubMed CentralGoogle Scholar
- Gonzalez HE, Eugenin EA, Garces G, Solis N, Pizarro M, Accatino L, et al. Regulation of hepatic connexins in cholestasis: possible involvement of Kupffer cells and inflammatory mediators. Am J Physiol Gastrointest Liver Physiol. 2002;282:G991–G1001.View ArticlePubMedGoogle Scholar
- Bradford MM. A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding. Anal Biochem. 1976;72:248–54.View ArticlePubMedGoogle Scholar
- Eugenin EA, Gonzalez H, Saez CG, Saez JC. Gap junctional communication coordinates vasopressin-induced glycogenolysis in rat hepatocytes. Am J Physiol. 1998;274:G1109–1116.PubMedGoogle Scholar
- Carvallo L, Henriquez B, Paredes R, Olate J, Onate S, van Wijnen AJ, et al. 1alpha,25-dihydroxy vitamin D3-enhanced expression of the osteocalcin gene involves increased promoter occupancy of basal transcription regulators and gradual recruitment of the 1alpha,25-dihydroxy vitamin D3 receptor-SRC-1 coactivator complex. J Cell Physiol. 2008;214:740–9.View ArticlePubMedGoogle Scholar
- Geimonen E, Jiang W, Ali M, Fishman GI, Garfield RE, Andersen J. Activation of protein kinase C in human uterine smooth muscle induces connexin-43 gene transcription through an AP-1 site in the promoter sequence. J Biol Chem. 1996;271:23667–74.View ArticlePubMedGoogle Scholar
- Essenfelder GM, Larderet G, Waksman G, Lamartine J. Gene structure and promoter analysis of the human GJB6 gene encoding connexin 30. Gene. 2005;350:33–40.View ArticlePubMedGoogle Scholar
- Eugenin EA, Berman JW. Cytochrome C dysregulation induced by HIV infection of astrocytes results in bystander apoptosis of uninfected astrocytes by an IP and calcium dependent mechanism. J Neurochem. 2013;127(5):644–51.View ArticlePubMedPubMed CentralGoogle Scholar
- Orellana JA, Saez JC, Bennett MV, Berman JW, Morgello S, Eugenin EA. HIV increases the release of dickkopf-1 protein from human astrocytes by a Cx43 hemichannel-dependent mechanism. J Neurochem. 2013.Google Scholar
- Duffy HS, John GR, Lee SC, Brosnan CF, Spray DC. Reciprocal regulation of the junctional proteins claudin-1 and connexin43 by interleukin-1beta in primary human fetal astrocytes. J Neurosci. 2000;20:RC114.PubMedGoogle Scholar
- Karn J. Tackling Tat. J Mol Biol. 1999;293:235–54.View ArticlePubMedGoogle Scholar
- Fujinaga K, Taube R, Wimmer J, Cujec TP, Peterlin BM. Interactions between human cyclin T, Tat, and the transactivation response element (TAR) are disrupted by a cysteine to tyrosine substitution found in mouse cyclin T. Proc Natl Acad Sci U S A. 1999;96:1285–90.View ArticlePubMedPubMed CentralGoogle Scholar
- Mousseau G, Mediouni S, Valente ST. Targeting HIV transcription: the quest for a functional cure. Curr Top Microbiol Immunol. 2015;389:121–45.PubMedPubMed CentralGoogle Scholar
- Bachani M, Sacktor N, McArthur JC, Nath A, Rumbaugh J. Detection of anti-tat antibodies in CSF of individuals with HIV-associated neurocognitive disorders. J Neurovirol. 2013;19:82–8.View ArticlePubMedPubMed CentralGoogle Scholar
- Zayyad Z, Spudich S. Neuropathogenesis of HIV: from initial neuroinvasion to HIV-associated neurocognitive disorder (HAND). Curr HIV/AIDS Rep. 2015;12:16–24.View ArticlePubMedPubMed CentralGoogle Scholar
- Elbirt D, Mahlab-Guri K, Bezalel-Rosenberg S, Gill H, Attali M, Asher I. HIV-associated neurocognitive disorders (HAND). Isr Med Assoc J. 2015;17:54–9.PubMedGoogle Scholar
- King JE, Eugenin EA, Buckner CM, Berman JW. HIV tat and neurotoxicity. Microbes Infect. 2006;8:1347–57.View ArticlePubMedGoogle Scholar
- Nath A, Steiner J. Synaptodendritic injury with HIV-Tat protein: what is the therapeutic target? Exp Neurol. 2014;251:112–4.View ArticlePubMedGoogle Scholar
- Al-Harthi L. Interplay between Wnt/beta-Catenin signaling and HIV: virologic and biologic consequences in the CNS. Journal of neuroimmune pharmacology : the official journal of the Society on NeuroImmune Pharmacology. 2012.Google Scholar
- Carroll-Anzinger D, Kumar A, Adarichev V, Kashanchi F, Al-Harthi L. Human immunodeficiency virus-restricted replication in astrocytes and the ability of gamma interferon to modulate this restriction are regulated by a downstream effector of the Wnt signaling pathway. J Virol. 2007;81:5864–71.View ArticlePubMedPubMed CentralGoogle Scholar
- Li W, Henderson LJ, Major EO, Al-Harthi L. IFN-gamma mediates enhancement of HIV replication in astrocytes by inducing an antagonist of the beta-catenin pathway (DKK1) in a STAT 3-dependent manner. J Immunol. 2011;186:6771–8.View ArticlePubMedPubMed CentralGoogle Scholar
- Richards MH, Narasipura SD, Kim S, Seaton MS, Lutgen V, Al-Harthi L. Dynamic interaction between astrocytes and infiltrating PBMCs in context of neuroAIDS. Glia. 2015;63:441–51.View ArticlePubMedPubMed CentralGoogle Scholar
- Allen K, Fuchs EC, Jaschonek H, Bannerman DM, Monyer H. Gap junctions between interneurons are required for normal spatial coding in the hippocampus and short-term spatial memory. J Neurosci. 2011;31:6542–52.View ArticlePubMedPubMed CentralGoogle Scholar
- Bissiere S, Zelikowsky M, Ponnusamy R, Jacobs NS, Blair HT, Fanselow MS. Electrical synapses control hippocampal contributions to fear learning and memory. Science. 2011;331:87–91.View ArticlePubMedPubMed CentralGoogle Scholar
- Jiang S, Wang YQ, Xu CF, Li YN, Guo R, Li L. Involvement of connexin43 in the infrasonic noise-induced glutamate release by cultured astrocytes. Neurochem Res. 2014;39:833–42.View ArticlePubMedGoogle Scholar
- Lutz SE, Zhao Y, Gulinello M, Lee SC, Raine CS, Brosnan CF. Deletion of astrocyte connexins 43 and 30 leads to a dysmyelinating phenotype and hippocampal CA1 vacuolation. J Neurosci. 2009;29:7743–52.View ArticlePubMedPubMed CentralGoogle Scholar
- Stehberg J, Moraga-Amaro R, Salazar C, Becerra A, Echeverria C, Orellana JA, et al. Release of gliotransmitters through astroglial connexin 43 hemichannels is necessary for fear memory consolidation in the basolateral amygdala. FASEB J. 2012;26:3649–57.View ArticlePubMedGoogle Scholar
- Wang Y, Belousov AB. Deletion of neuronal gap junction protein connexin 36 impairs hippocampal LTP. Neurosci Lett. 2011;502:30–2.View ArticlePubMedPubMed CentralGoogle Scholar
- Velasquez S, Eugenin EA. Role of Pannexin-1 hemichannels and purinergic receptors in the pathogenesis of human diseases. Front Physiol. 2014;5:96.View ArticlePubMedPubMed CentralGoogle Scholar
- Lin JH, Weigel H, Cotrina ML, Liu S, Bueno E, Hansen AJ, et al. Gap-junction-mediated propagation and amplification of cell injury. Nat Neurosci. 1998;1:494–500.View ArticlePubMedGoogle Scholar
- Azzam EI, de Toledo SM, Gooding T, Little JB. Intercellular communication is involved in the bystander regulation of gene expression in human cells exposed to very low fluences of alpha particles. Radiat Res. 1998;150:497–504.View ArticlePubMedGoogle Scholar
- Chen ZQ, Lefebvre D, Bai XH, Reaume A, Rossant J, Lye SJ. Identification of two regulatory elements within the promoter region of the mouse connexin 43 gene. J Biol Chem. 1995;270:3863–8.View ArticlePubMedGoogle Scholar
- Yu W, Dahl G, Werner R. The connexin43 gene is responsive to oestrogen. Proc Biol Sci. 1994;255:125–32.View ArticlePubMedGoogle Scholar
- He G, Ylisastigui L, Margolis DM. The regulation of HIV-1 gene expression: the emerging role of chromatin. DNA Cell Biol. 2002;21:697–705.View ArticlePubMedGoogle Scholar