Antiapoptotic Function of Cdk9 (TAK/P-TEFb) in U937 Promonocytic Cells

Cdk9 is the catalytic subunit of TAK (cyclinT1/P-TEFb), a cellular protein kinase that mediates human immunodeficiency virus type 1 (HIV-1) Tat transcriptional activation function. To examine Cdk9 function in cells relevant to HIV-1 infection, we used a murine leukemia virus retrovirus vector to transduce and overexpress the cDNA of a dominant negative mutant Cdk9 protein (Cdk9-dn) in Jurkat T cells and U937 promonocytic cells. In Jurkat cells, overexpression of Cdk9-dn specifically inhibited Tat transactivation and HIV-1 replication but had no inhibitory effect on induction of CD69, CD25, and interleukin-2 following T-cell activation. In U937 cells, overexpression of Cdk9-dn sensitized cells to apoptosis, especially after phorbol myristate acetate (PMA) treatment to induce differentiation to macrophage-like cells. Because Cdk9 function is induced in PMA-treated U937 cells, Cdk9 may play an antiapoptotic role during monocyte differentiation.