Unraveling the molecular link between HIVAIDS and cancer

Division Of Basic Sciences - Nci

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Abstract

Our unbiased proteomic mass spectrometry and subsequent biochemical analyses showed that Plk4 binds to the C-terminal acidic domain (1401-1507) of a cellular scaffold protein, VprBP, via its C-terminal cryptic polo-box. Strikingly, HIV-1 Vpr, which binds to the WD40 domain (1003-1400) of VprBP, greatly enhanced the VprBP-Plk4 interaction and induced the formation of the Vpr-VprBP-Plk4 complex. All three proteins colocalized to centrosomes, and the ternary complex formation appeared to augment Plk4-mediated centriole duplication. Consistent with these findings, VprBP promoted Plk4 function by stabilizing its centriole-associated state rather than inducing its proteasomal degradation, as was observed for the Vpx-VprBP-SAMHD1 complex and other cellular targets. These data suggest that when cells are infected with HIV-1, Vpr may alter Plk4's function by forming the Vpr-VprBP-Plk4 complex under physiological conditions and induce Plk4-dependent centriole overduplication, a cellular event causing aneuploidy and cancer. A structurally related HIV-2 Vpx failed to interact with VprBP and Plk4, indicating the specificity of HIV-1 Vpr-induced events. Based on these observations, we postulate that HIV-1 Vpr can directly alter genomic stability and facilitate carcinogenesis by hijacking the cellular Plk4-VprBP complex. Additional studies are planned to determine the role of the ternary Vpr-VprBP-Plk4 complex under physiologically relevant conditions using HIV-1-susceptible cells and tissues in animal models. This research could shed light on the mechanism that could directly link HIV/AIDS to the etiology of its comorbid cancers. Furthermore, it may offer a new paradigm in understanding the increased cancer risk in people with HIV-1. Investigating HIV-induced comorbidities is one of the four designated NIH HIV/AIDS research priorities. This research is designed to directly address HIV-1-associated cancer comorbidities. We have gained an enriched experience in studying how HIV proteins interact with cellular targets and alter cell physiology using various biochemical and structure-based analyses. Furthermore, our efforts to determine the quaternary structure of the Vpr-VprBP-Plk4 complex have been moving along well. Once the quaternary structure is determined, we will be interested in designing inhibitors that could disrupt the complex and thus help prevent HIV-1-induced centrosomal abnormalities and their associated human disorders, such as cancer. The data that we obtained from various cultured cells revealed that disrupting the Vpr-VprBP-Plk4 complex by either deleting the Vpr's C-terminal tail or the VprBP's acidic region was sufficient to abolish Vpr-dependent centrosome amplification and aneuploidy in multiple CD4+ cells, including primary T cells. Given the tight association of aneuploidy and cancer, these findings suggest that the HIV-1-induced Vpr-VprBP-Plk4 complex can directly promote oncogenesis in HIV-1-susceptible T cells or other blood Vpr-transducible cells by hijacking the host machinery for Plk4-mediated centriole duplication. In light of the finding that the risk of developing NHL remains high even during the combination antiretroviral therapy, this work may offer a new direction for investigating underlying mechanisms that give rise to HIV-1-associated cancers.