- Short report
- Open Access
Activation of HIV-1 expression and replication by cGMP dependent protein kinase type 1-β (PKG1β)
Retrovirology volume 4, Article number: 91 (2007)
The effect of cGMP (cyclic GMP) dependent protein kinase 1-β (PKG1-β) and cGMP analogues on transcriptional activity and replication of human immunodeficiency virus type 1 (HIV-1) was investigated. Transfection of PKG1β expression plasmid increased expression from an HIV-1 LTR-reporter as well as from an infectious HIV-1 molecular clone, pNL4-3. Treatment of HIV-1 AD8-infected monocyte derived macrophages (MDMs) with cGMP agonists and cGMP antagonists caused respectively increased and decreased virus replication. These findings provide evidence that cGMP and PKG serve to regulate HIV-1 infection in human cells.
Previously nitric oxide (NO) was postulated to have a negative effect on HIV-1 replication through a cGMP-independent route . However, it was not characterized as to how this cGMP-independent effect manifested mechanistically. On the other hand, it is well-accepted that a major intracellular signaling pathway for NO is through a cytosolic-guanylate cyclase linked cGMP-dependent protein kinase, PKG, pathway . cGMP/PKG has been shown to activate abundantly both CREB  and NF-κB [4, 5]. Interestingly, to our knowledge, no systematic investigation of cGMP/PKG's activity on the HIV-1 LTR has been reported to date.
To address how cGMP/PKG might influence HIV-1 LTR-directed expression, we transfected HeLa cells with a LTR-luciferase reporter with or without a Tat-plasmid [6–9]- and assayed for expression with or without simultaneously co-transfecting a PKG1β-expression vector - (Figure 1). We found that PKG1β-alone activated reporter expression by approximately 4 fold (also see Figure 2B) while Tat-alone activated expression by >45 fold (Figure 1A). Co-transfection of LTR-luciferase + Tat + PKG1β activated expression cumulatively to >175 fold (Figure 1A). These results are consistent with PKG1β inducing LTR-driven expression whether in the absence or presence of Tat.
To verify more physiologically the above LTR-reporter assay, we next checked the effect of PKG1β on an HIV-1 infectious molecular clone, pNL 4-3 (Figure 1B). Here, increasing amounts of PKG1β-plasmid were transfected into cells with a constant level of pNL 4-3. Viral proteins expressed from the HIV-1 molecular clone were then measured. Using HIV-specific hyper-immune sera in Western blots, we observed that PKG1β increased pNL 4-3 expression in a dose dependent manner (Figure 1B, lanes 2 – 6). To investigate whether the intact function of PKG1β was needed for this activity, we created two loss-of-function PKG1β deletion mutants (Figure 2A). Both deletion mutants were unable to activate either a LTR-reporter (Figure 2B) or an HIV-1 infectious molecular clone (Figure 2C).
Optimal PKG activity is dependent on activation by cGMP . While over expression of exogenously transfected PKG offered significantly measureable effects (Figures 1, 2), we wished to understand next how cell endogenous PKG might act mechanistically in response to cGMP treatment. Elsewhere, it was reported that NF-κB p65, p52, and p50 are substrate proteins activated by PKG-mediated phosphorylation. Because expression of the HIV-1 LTR is regulated by NF-κB [12, 13], we asked if cGMP activated NF-κB in our experimental.
To assess if NF-κB was activated by cGMP, we assayed for enhanced nuclear localization of NF-κB protein p65, which is one measure of activation [14, 15]. We treated cells with a cGMP agonist, 8-pCPT-cGMP, and compared results to cells treated with a known NF-κB activator, tumor necrosis factor alpha, TNFα. When cytosolic and nuclear p65 proteins were assayed, we observed that 8-pCPT-cGMP behaved quantitatively very similarly to TNFα in inducing increased NF-κB p65-translocation into the nucleus (Figure 3A). This result supports that PKG-activation of HIV-1 (Figures 1, 2) acts through an NF-κB-mediated process. To confirm that PKG1β can directly activate NF-κβ activity, we transfected a NF-κβ luciferase reporter into cells with or without a co-transfected PKG1β expression plasmid (Figure 3B). Results from this assay showed that NF-κβ-dependent luciferase activity was indeed elevated by PKG1β.
A more direct verification of cGMP/PKG's role in HIV-1 replication can be established using chemical agonists and antagonists of this pathway seeking for effects on viral infection. Because the NO/cGMP signaling pathway has been reported to function potently in cells of macrophage lineage, we performed infection of monocyte derived macrophages (MDMs) using HIV-1 strain AD8 [16, 17]. MDMs infected with AD8 were treated individually with three different drugs. We employed two cGMP agonists (8-pCPT-cGMP, and Sp-8-pCPT-cGMP) and one cGMP antagonist (Rp-8-pCPT-cGMPs) and monitored their impact on HIV-1 replication. Informatively, in two separate experiments, both agonist drugs increased virus replication over control-treated infection, while the cGMP-antagonist drug decreased (or did not affect) virus replication (Figure 4).
Here, we report evidence that both in the absence and presence of Tat the cGMP/PKG pathway can serve to modulate HIV-1 expression/replication. Understanding how HIV-1 LTR expression is affected by ambient cellular pathways [18–20] may help to address potential approaches for treating latent HIV-1 infection . The current findings may be important because cGMP is a ubiquitous second messenger that affects multiple cellular pathways in most, if not all, cells. Accordingly, cGMP-influenced pathways are likely to interdigitate with some of the signaling routes utilized by HIV-1 in infected cells . Additionally, because many cGMP chemical agonists and antagonists are available [23, 24], practical chemotherapeutic interventions in these pathways (if they should be useful for anti-viral purposes) could be amenable.
Mannick JB, Stamler JS, Teng E, Simpson N, Lawrence J, Jordan J, Finberg RW: Nitric oxide modulates HIV-1 replication. J Acquir Immune Defic Syndr. 1999, 22: 1-9.
Denninger JW, Marletta MA: Guanylate cyclase and the .NO/cGMP signaling pathway. Biochim Biophys Acta. 1999, 1411: 334-350. 10.1016/S0005-2728(99)00024-9.
Gudi T, Casteel DE, Vinson C, Boss GR, Pilz RB: NO activation of fos promoter elements requires nuclear translocation of G-kinase I and CREB phosphorylation but is independent of MAP kinase activation. Oncogene. 2000, 19: 6324-6333. 10.1038/sj.onc.1204007.
He B, Weber GF: Phosphorylation of NF-kappaB proteins by cyclic GMP-dependent kinase. A noncanonical pathway to NF-kappaB activation. Eur J Biochem. 2003, 270: 2174-2185. 10.1046/j.1432-1033.2003.03574.x.
He B, Weber GF: Synergistic activation of the CMV promoter by NF-kappaB P50 and PKG. Biochem Biophys Res Commun. 2004, 321: 13-20. 10.1016/j.bbrc.2004.06.101.
Jeang KT, Berkhout B: Kinetics of HIV-1 long terminal repeat trans-activation. Use of intragenic ribozyme to assess rate-limiting steps. J Biol Chem. 1992, 267: 17891-17899.
Jeang KT, Berkhout B, Dropulic B: Effects of integration and replication on transcription of the HIV-1 long terminal repeat. J Biol Chem. 1993, 268: 24940-24949.
Brady J, Kashanchi F: Tat gets the "green" light on transcription initiation. Retrovirology. 2005, 2: 69-10.1186/1742-4690-2-69.
Ammosova T, Berro R, Jerebtsova M, Jackson A, Charles S, Klase Z, Southerland W, Gordeuk VR, Kashanchi F, Nekhai S: Phosphorylation of HIV-1 Tat by CDK2 in HIV-1 transcription. Retrovirology. 2006, 3: 78-10.1186/1742-4690-3-78.
Sandberg M, Natarajan V, Ronander I, Kalderon D, Walter U, Lohmann SM, Jahnsen T: Molecular cloning and predicted full-length amino acid sequence of the type I beta isozyme of cGMP-dependent protein kinase from human placenta. Tissue distribution and developmental changes in rat. FEBS Lett. 1989, 255: 321-329. 10.1016/0014-5793(89)81114-7.
Pilz RB, Broderick KE: Role of cyclic GMP in gene regulation. Front Biosci. 2005, 10: 1239-1268. 10.2741/1616.
Nabel G, Baltimore D: An inducible transcription factor activates expression of human immunodeficiency virus in T cells. Nature. 1987, 326: 711-713. 10.1038/326711a0.
Berkhout B, Jeang KT: Functional roles for the TATA promoter and enhancers in basal and Tat-induced expression of the human immunodeficiency virus type 1 long terminal repeat. J Virol. 1992, 66: 139-149.
Vermeulen L, De WG, Notebaert S, Vanden BW, Haegeman G: Regulation of the transcriptional activity of the nuclear factor-kappaB p65 subunit. Biochem Pharmacol. 2002, 64: 963-970. 10.1016/S0006-2952(02)01161-9.
Peloponese JM, Yeung ML, Jeang KT: Modulation of nuclear factor-kappaB by human T cell leukemia virus type 1 Tax protein: implications for oncogenesis and inflammation. Immunol Res. 2006, 34: 1-12. 10.1385/IR:34:1:1.
Freed EO, Martin MA: HIV-1 infection of non-dividing cells. Nature. 1994, 369: 107-108. 10.1038/369107b0.
Rich EA, Orenstein JM, Jeang KT: A macrophage-tropic HIV-1 that expresses green fluorescent protein and infects alveolar and blood monocyte-derived macrophages. J Biomed Sci. 2002, 9: 721-726. 10.1007/BF02255001.
Agbottah E, Deng L, Dannenberg LO, Pumfery A, Kashanchi F: Effect of SWI/SNF chromatin remodeling complex on HIV-1 Tat activated transcription. Retrovirology. 2006, 3: 48-10.1186/1742-4690-3-48.
Ariumi Y, Serhan F, Turelli P, Telenti A, Trono D: The integrase interactor 1 (INI1) proteins facilitate Tat-mediated human immunodeficiency virus type 1 transcription. Retrovirology. 2006, 3: 47-10.1186/1742-4690-3-47.
Sorin M, Yung E, Wu X, Kalpana GV: HIV-1 replication in cell lines harboring INI1/hSNF5 mutations. Retrovirology. 2006, 3: 56-10.1186/1742-4690-3-56.
Marcello A: Latency: the hidden HIV-1 challenge. Retrovirology. 2006, 3: 7-10.1186/1742-4690-3-7.
Fassati A: HIV infection of non-dividing cells: a divisive problem. Retrovirology. 2006, 3: 74-10.1186/1742-4690-3-74.
Bender AT, Beavo JA: Cyclic nucleotide phosphodiesterases: molecular regulation to clinical use. Pharmacol Rev. 2006, 58: 488-520. 10.1124/pr.58.3.5.
Martelli A, Rapposelli S, Calderone V: NO-releasing hybrids of cardiovascular drugs. Curr Med Chem. 2006, 13: 609-625. 10.2174/092986706776055634.
Work in Kuan-Teh Jeang's laboratory is supported in part by intramural funding from NIAID, NIH; and by the intramural AIDS targeted antiviral program (IATAP) from the Office of the Director, NIH. We thank Dr. S.M. Lohmann for PKG1β expression plasmid.
The author(s) declare that they have no competing interests.
JHL and VY carried out the experiments. JHL, VY, and KTJ conceived of the study and wrote the manuscript.
About this article
Cite this article
Lee, J.H., Yedavalli, V.R. & Jeang, KT. Activation of HIV-1 expression and replication by cGMP dependent protein kinase type 1-β (PKG1β). Retrovirology 4, 91 (2007). https://doi.org/10.1186/1742-4690-4-91
- Chemical Agonist
- Increase Virus Replication
- Decrease Virus Replication
- cGMP Dependent Protein Kinase Type
- Activate Reporter Expression