p38MAP kinase is a negative regulator for ERK1/2-mediated growth of AIDS-associated Kaposi's sarcoma cells.

AIDS-associated Kaposi's sarcoma (KS) is a cytokine-mediated tumor, at least in the early stages of this disease; however, there is at present no definitive consensus regarding the exact role of intracellular signaling pathways involved in growth of KS cells. We found that KS cell growth factors oncostatin M, sIL-6R/IL-6, TNFalpha, and IL-1beta all activate ERK1/2, and selective blockage of this kinase by PD98059 resulted in a profound inhibition of the cytokine-induced KS cell growth. Concurrently with activation of ERK1/2, these growth factors phosphorylated and activated p38MAPK. The selective inhibition of p38MAPK by SB203580 prominently enhanced the cytokine-induced proliferation of KS cells, thereby indicating that p38MAPK has a negative feedback on mitogenic signals. As these KS cell growth factors lead to simultaneous activation of ERK1/2 and p38MAPK signaling pathways, the concerted effects of these kinase activities may well determine the intensity of cellular proliferative responses to these growth factors.