Role of cellular RNA processing factors on HIV - 1 mRNA metabolism , replication and infectivity

Expression of the HIV-1 genome requires several cellular factors regulating transcription, alternative splicing, RNA stability and intracellular localization of the viral transcripts. In-vitro and ex-vivo approaches have identified SR proteins and hnRNPs of the A/B and H subfamilies as cellular factors that regulate different aspects of viral mRNA metabolism. To understand the role of these protein families within the context of the full replicating virus we altered the expression levels of A3 and SR proteins SC35, SF2, SRp40 in HEK-293 cells transfected with the proviral clone pNL4-3. Quantitative and semi-quantitative PCR analysis showed that over-expression as well as down-regulation of these proteins disrupted the balance of alternatively spliced viral mRNAs and may alter viral transcription. Furthermore, localization of the unspliced Gag/Pol mRNA, while the same factors increased the cytoplasmic localization of the partially spliced Env mRNA. We also report that over-expression of hnRNPs A1, A2 and SR proteins SF2, SC35 and SRp40 causes a dramatic decrease in virion production. Finally, utilizing a reporter TZM-bl cell line we show that virion infectivity may be also impacted by deregulation of expression of most SR and hnRNP proteins. This work demonstrates that cellular factors regulating mRNA processing have wide-ranging effects on HIV-1 replication and should be considered as novel therapeutic targets.