The Role And Mechanism Of Calcium Signal Pathway In HIV-1 Transcription

In eukaryotic cells, the transcription of messenger RNA (mRNA) from protein-coding genes is performed by RNA polymerase II, the carboxy-terminal domain (CTD) of the largest subunit of RNA Pol II is phosphorylated. P-TEFb, a heterodimer consisting with cyclin T and CDK9, who plays an unique and important role in transcription elongation of eukaryotes,targets Ser2 of CTD for phosphorylation.In human Hela cells, the regulation of PTEFb activity is a dynamic and tightly controlled process involving the P-TEFb-associated factors HEXIM1, an inhibitor of P-TEFb activities when associated with 7SK snRNA. The HEXIM1-free form of P-TEFb accounts for about half of total P-TEFb in the cell, which can function as both a general and HIV-specific transcription factor. In contrast, the HEXIM1-bound P-TEFb is inactive as its kinase and transcriptional activities are suppressed.Besides functioning as a general elongation factor capable of overcome the pausing of Pol II during early elongation, P-TEFb plays an important role in HIV-Tat transcription. Tat stimulates polymerase elongation by recognizing the HIV TAR RNA structure and recruiting P-TEFb to the HIV promoter.Calcium signal pathway always plays an important role in mRNA transcription. It was reported that overexpression of the constitutively active form of calcineurin A(one of the important proteins of calcium signal pathway) in transgenic mice leaded to the activation of P-TEFb in the myocardium, suggesting the role of calcium signal pathway in the controling of gene transcription.In our study, we apply several kinds of inhibitors of the calcium signal pathway to reaserch the role and the mechanism of it in the HIV—1 transcription regulation. We identified the necessity of calcium-—calmodulin—- calcineurin pathway and the cooperation of calcineurin with PP1 in the 7SK snRNP disassociation as well as in the activation of HIV—1 transcripton. And the fact that calcineurin and PP1 function cooperatively to disrupt 7SK snRNP and stimulate HIV—1 transactivation.