A role for RNA helicase A in post-transcriptional regulation of HIV type 1

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Abstract
Retroviruses must bypass the tight coupling of splicing and nuclear export of mRNA in their replication cycle because unspliced genomic RNA and incompletely spliced mRNA must be exported to the cytoplasm for packaging or translation. This process is mediated by a cis-acting constitutive transport element (CTE) for simple retroviruses and by the trans-acting viral protein Rev in concert with its response element (RRE) for complex retroviruses (e.g., HIV). Recently, we identified RNA helicase A (RHA) as a potential cellular cofactor for CTE. Here, we report that RHA also plays a role in Rev/RRE-mediated gene expression and HIV replication. RHA binds weakly to HIV-1 RRE independently of Rev. Overexpression of RHA, but not of an RHA mutant lacking helicase activity, increased both Rev/RRE- and CTE-dependent gene expression and the levels of unspliced HIV mRNA. Microinjection of antibodies to RHA into nuclei dramatically inhibited both CTE- and Rev-dependent gene expression in human cells. Exogenous RHA cDNA, but not the mutant RHA, rescued this inhibition. We propose that RHA is required to release both CTE- and RRE-containing mRNA from spliceosomes before completion of splicing, thus freeing them for nuclear export.