HSP 70 binding protein 1 ( HspBP 1 ) suppresses HIV-1 replication by inhibiting NF-B mediated activation of viral gene expression

HIV-1 efficiently hijacks host cellular machinery and exploits a plethora of host–viral interactions for its successful survival. Identifying host factors that affect susceptibility or resistance to HIV-1 may offer a promising therapeutic strategy against HIV-1. Previously, we have reported that heat shock proteins, HSP40 and HSP70 reciprocally regulate HIV-1 geneexpression and replication. In the present study, we have identified HSP70 binding protein 1 (HspBP1) as a host-intrinsic inhibitor of HIV-1. HspBP1 level was found to be significantly down modulated during HIV1 infection and virus production inversely co-related with HspBP1 expression. Our results further demonstrate that HspBP1 inhibits HIV-1 long terminal repeat (LTR) promoter activity. Gel shift and chromatin immunoprecipitation assays revealed that HspBP1 was recruited on HIV-1 LTR at NFB enhancer region ( B sites). The binding of HspBP1 to B sites obliterates the binding of NFB hetero-dimer (p50/p65) to the same region, leading to repression in NFB mediated activation of LTR-driven gene-expression. HspBP1 also plays an inhibitory role in the reactivation of latently infected cells, corroborating its repressive effect on NFB pathway. Thus, our results clearly show that HspBP1 acts as an endogenous negative regulator of HIV-1 gene-expression and replication by suppressing NFB-mediated activation of viral transcription. INTRODUCTION Human immunodeficiency virus-1 (HIV-1) continues to be a successful pathogen for the last three decades, owing to its ability to undergo frequent mutations and the capability to manipulate host cell micro-environment to its advantage. The virus employs multiple strategies to escape the host immune system including latency (1), inhibition of antigen processing and presentation (2) and high rate of mutations (3) to avoid recognition by immune molecules (4). Moreover, highly evolved accessory proteins add to its pathogenicity (5). It has a relatively small genome, approximately 9.8 kb in length that encodes 15 proteins. Therefore, in addition to its own proteins, HIV-1 exploits various host cellular proteins for successful completion of its life cycle. Genome-wide studies including siRNAand shRNA screens (6–10), protein-protein interactions (11–14), bio-informatic analysis with patient samples (15–18) and meta-analysis of genome-wide studies (19) have revealed the significance of over a thousand cellular proteins in HIV-1 replication and gene-expression. In past 30 years, viral enzymes (including reverse transcriptase, integrase and protease) have been extensively targeted to develop therapeutics against HIV. Although the combination therapy of these anti-retrovirals have worked well for the management of the disease but issues related to drug resistance and cellular toxicity have induced researchers to look for novel therapeutic targets (20). As mentioned above, in recent years, a large number of cellular factors have been shown to be absolutely essential for HIV-1 life cycle. Thus, targeting such host cellular factors required for successful infection and propagation of the virus in addition to currently available anti-retrovirals might offer a better therapeutic strategy. The gene expression of HIV-1 is tightly regulated by interaction of numerous host cellular proteins with cis*To whom correspondence should be addressed. Tel: +91 2