HIV-1 Replication and Latency Are Regulated by Translational Control of Cyclin T1

Abstract

HIV exploits cellular proteins during its replicative cycle and latent infection. The positive transcription elongation factor, P-TEFb, is a key cellular transcription factor critical for these viral processes and is a drug target. During viral replication P-TEFb is recruited via interactions of its cyclin T1 subunit with the HIV Tat protein and TAR element. Through RNA silencing and over-expression experiments we discovered that nuclear factor 90 (NF90), a cellular RNA binding protein, regulates P-TEFb expression. NF90 depletion reduced cyclin T1 protein levels by inhibiting translation initiation. Regulation was mediated by the 3′UTR of cyclin T1 mRNA independently of microRNAs. Cyclin T1 induction is involved in the escape of HIV-1 from latency. We show that the activation of viral replication by phorbol ester in latently infected monocytic cells requires the posttranscriptional induction of NF90 and cyclin T1, implicating NF90 in protein kinase C (PKC) signaling pathways. This investigation reveals a novel mechanism of cyclin T1 regulation and establishes NF90 as a regulator of HIV-1 replication during both productive infection and induction from latency.

NF90 Exerts Antiviral Activity through Regulation of PKR Phosphorylation and Stress Granules in Infected Cells

“…NF90 was shown to inhibit replication of a broad range of viruses and to form complexes with NF45 and shuttle between the nucleus and cytoplasm (13)(14)(15)(16)(17)(18)(19). However, a detailed mechanism describing how NF90 negatively regulates virus replication remains unclear.…”

“…It suppresses the function of Ebola virus polymerases through interaction with VP35 (14), inhibits HIV replication through interaction with HIV-1 TAR RNA (15,16), represses internal ribosome entry sites in rhinoviruses (17,18) and negatively regulates influenza virus replication through interaction with viral nucleoprotein (NP) (19). However, other studies (20)(21)(22)(23) found that NF90 is required for the replication of some positivestranded RNA viruses and is important for expression of E6 protein in human papillomavirus-infected cells.…”

Cyclin T1 and CDK9 T-Loop Phosphorylation Are Downregulated during Establishment of HIV-1 Latency in Primary Resting Memory CD4+T Cells

“…The transcription-independent increase in Cyclin T1 protein levels is in part due to regulation by differentially expressed miRNAs (11). However, translation initiation from the Cyclin T1 3= untranslated region (UTR) has also been shown to be regulated by an RNA binding protein, NF90, independently of miRNAs in certain cell lines (34). In late differentiated macrophages, Cyclin T1 protein expression is regulated by proteasomemediated proteolysis, indicating that multiple mechanisms regulate Cyclin T1 protein expression (35).…”

Progress and challenges in the use of latent HIV-1 reactivating agents

“…Latency can be maintained at transcriptional levels (eg, lack of transcriptional activators, condensed chromatin structure) or at post-transcriptional levels (eg, inhibition of nuclear RNA transport and inhibition of translation by microRNA), and it is generally assumed that maintenance at the transcriptional level is the case for the majority of latently infected cells. Molecular mechanisms targeting transcription consist of both trans-effects and cis-effects, including: (1) the chromatin environment around the integration site and transcriptional interference [17,18] ; (2) the epigenetic control of the HIV-1 promoter or the presence of repressive nucleosomes (nuc-0 and nuc-1) [19,20] ; (3) lack of crucial transcriptional factors, such as NF-κB or nuclear factor of activated T cells (NFAT) [21] , sub-optimal concentrations of transcriptional activators such as Tat [22,23] or the presence of transcriptional suppressors such as CTIP2 (COUPTF Interacting Protein 2) [24,25] , DSIF (DRB-Sensitivity Inducing Factor) [26] and NELF (Negative Elongation Factor) [27] ; (4) the sequestration of positive transcriptional elongation factor b (P-TEFb) in its inactive form with HEXIM [hexamethylene bisacetamide (HMBA)-induced protein 1] and 7SK snRNA (small nuclear RNA) [28][29][30] .…”