Mutational analysis of HIV-2 Vpx shows that proline residue 109 in the poly-proline motif regulates degradation of SAMHD1

Discovery of anti-cell migration activity of an anti-HIV heterocyclic compound by identification of its binding protein hnRNP M

One compound sometimes shows two biological functions, becoming important aspect of recent drug discovery. This study began with an attempt to confirm the previously reported molecular mechanism of the anti-human immunodeficiency virus (HIV) heterocyclic compound BMMP [2-(benzothiazol-2-ylmethylthio)-4-methylpyrimidine], i.e., induction of abnormal uncoating of the viral core at the post-entry step. Our mechanistic study gave results consistent with this mechanism. We further attempted to find out the molecular target of BMMP by a pulldown approach using previously synthesized biotinylated BMMP (Biotin-BMMP) and successfully identified heterogenous nuclear ribonucleoprotein M (hnRNP M) as a BMMP-binding protein. This protein was found not to be accountable for the anti-HIV activity of BMMP. As hnRNP M has been reported to promote cancer metastasis, we tested this mechanism and found that BMMP suppressed migration of the human lung carcinoma cell line A549 stimulated with transforming growth factor-β (TGF-β). Mechanistic study showed that BMMP suppressed the expression of CD44 mRNA via the regulation of hnRNP M. Furthermore, six new derivatives of BMMP were synthesized, and the patterns of their activities against HIV-1 and cell migration were not uniform, suggesting that the anti-HIV mechanism and the anti-cell migration mechanism of BMMP are independent. Taken together, the anti-cell migration activity of the anti-HIV heterocyclic compound BMMP was newly discovered by identification of its binding protein hnRNP M using a chemical biology approach.

The stability of HIV-2 Vpx and Vpr proteins is regulated by the presence or absence of zinc-binding sites and poly-proline motifs with distinct roles

The Vpx and Vpr proteins of human immunodeficiency virus type 2 (HIV-2) are important for virus replication. Although these proteins are homologous, Vpx is expressed at much higher levels than Vpr. Previous studies demonstrated that this difference results from the presence of an HHCC zinc-binding site in Vpx that is absent in Vpr. Vpx has another unique region, a poly-proline motif (PPM) of seven consecutive prolines at the C-terminus. Using PPM point mutants of Vpx, this study demonstrated that these seven consecutive prolines are critical for suppressing proteasome degradation of Vpx in the absence of Gag. Both the PPM and the zinc-binding site stabilize Vpx but do so via different mechanisms. PPM and zinc-binding site mutants overexpressed in Escherichia coli aggregated readily, indicating that these motifs normally prevent exposure of the hydrophobic region outside the structure. Furthermore, introduction of the zinc-binding site and the PPM into Vpr increased the level of Vpr expression so that it was as high as that of Vpx. Intriguingly, HIV-2 has evolved to express Vpx at high levels and Vpr at low levels based on the presence and absence of these two motifs with distinct roles.

Radwan M, E. Ozturk S, Ulusoy NG, Sozer E, E. Ellakwa D, Ocak Z, Can M, F.S. Ali T, I. Abd-Alla H, Yayli N, Tateishi H, Otsuka M, Fujita M. Design, Synthesis and Biological Evaluation of Pentacyclic Triterpene Derivatives: Optimization of Anti-ABL Kinase Activity

Imatinib, an Abelson (ABL) tyrosine kinase inhibitor, is a lead molecular-targeted drug against chronic myelogenous leukemia (CML). To overcome its resistance and adverse effects, new inhibitors of ABL kinase are needed. Our previous study showed that the benzyl ester of gypsogenin (1c), a pentacyclic triterpene, has anti-ABL kinase and a subsequent anti-CML activity. To optimize its activities, benzyl esters of carefully selected triterpenes (PT1-PT6), from different classes comprising oleanane, ursane and lupane, and new substituted benzyl esters of gypsogenin (GP1-GP5) were synthesized. All of the synthesized compounds were purified and charachterized by different spectroscopic methods. Cytotoxicity of the parent triterpenes and the synthesized compounds against CML cell line K562 was examined; revealing three promising compounds PT5, GP2 and GP5 (IC50 5.46, 4.78 and 3.19 μM, respectively). These compounds were shown to inhibit extracellular signal-regulated kinase (ERK) downstream signaling, and induce apoptosis in K562 cells. Among them, PT5 was identified to have in vitro activity (IC50 = 1.44 μM) against ABL1 kinase, about sixfold of 1c, which was justified by molecular docking. The in vitro activities of GP2 and GP5 are less than PT5, hence they were supposed to possess other more mechanisms of cytotoxicity. In general, our design and derivatizations resulted in enhancing the activity against ABL1 kinase and CML cells.

The role of SAMHD1 expression and its relation to HIV-2 (Vpx) gene production

SAMHD1 (sterile alpha motif and HD domain 1) is a protein that is found in myeloid cells, which restricts HIV1 replication. It depletes the de-oxy-nucleoside tri-phosphate (dNTPs) pool needed for a viral cDNA synthesis leading to inhibition of viral replication inside the cells. However, it does not restrict HIV2 replication in myeloid cells due to the presence of viral Vpx protein. Vpx is a virion-associated protein which augments viral infectivity and it only exists in HIV2 and it has been recently shown in Simian Immunodeficiency Virus (SIV) and which can induce degradation of SAMHD1 protein. This increases the amount of dNTPs for viral reverse transcription in cytoplasm and HIV infection. HIV2 reverse transcription is believed to be less active than HIV1 and this could be the reason for the absence of Vpx from HIV1. Protein expression and interaction between Vpx and SAMHD1 remains unclear. The interaction of SAMHD1 and HIV2-VPx patients' cells can be considered as a first step to help in the development for more effective anti-HIV drugs and possible novel intervention therapy in the future. Present review article provides comprehensive insights on the above issue. We performed a comprehensive literature search in the bibliographic database “Pubmed,” looking at studies discussing the SAMHDI and Vpx interactions.

Introduction of H2C2-type zinc-binding residues into HIV-2 Vpr increases its expression level

Human immunodeficiency virus type 2 has two structurally similar proteins, Vpx and Vpr. Vpx degrades the host anti-viral protein SAMHD1 and is expressed at high levels, while Vpr is responsible for cell cycle arrest and is expressed at much lower levels. We constructed a Vpr mutant with a high level of expression by replacing the amino acids HHCR/HHCH with a putative H2C2-type zinc-binding site that is carried by Vpx. Our finding suggests that during the evolution of Vpr and Vpx, zinc-binding likely became a mechanism for regulating their expression levels.