Mitogenic signaling by cyclic adenosine monophosphate in chromaffin cells involves phosphatidylinositol 3-kinase activation

Increase of intracellular cyclic adenosine monophosphate by the permeant cy clic adenosine monophosphate analog, 8-(4-chlorophenylthio)-adenosine 3 ' : 5 '- cyclic monophosphate, is mitogenic for normal adult rat chromaffin cel ls. The mitogenic effect is blocked by the phosphatidylinositol 3-kinase in hibitor, LY294002, and is associated with accumulation of phosphorylated Ak t and p70S6 kinase, suggesting that cyclic adenosine monophosphate activate s Type I phosphatidylinositol 3-kinase. The mechanism of activation was exa mined in PC12 pheochromocytoma cells, which are neoplastic chromaffin cells that exhibit many of the biochemical characteristics of their normal count erparts. Incubation of PC12 cells with 8-(4-chlorophenylthio)-adenosine 3 ' :5 '- cyclic monophosphate led to a significant increase in total phosphat idylinositol 3-kinase activity that was sensitive to low concentrations of LY294002. The increase was maximal at 1 h and returned to basal levels with in six hours. Immunoprecipitation studies showed no increase in phosphatidy linositol 3-kinase activity in anti-phosphotyrosine immune complexes from P C12 cells stimulated by 8-(4-chlorophenylthio)-adenosine 3 ' :5 '- cyclic m onophosphate, in contrast to cells stimulated by nerve growth factor. Inste ad, activity was demonstrated in association with p110 gamma and p85. These findings suggest that cyclic adenosine monophosphate causes activation of Types IA and is phosphatidylinositol 3-kinase by a novel mechanism in chrom affin and pheochromocytoma cells. That activation may contribute to chromaf fin cell proliferation and to the development and progression of pheochromo cytomas. (C) 2001 Wiley-Liss, Inc.