Growth factor-induced phosphoinositide 3-OH kinase/Akt phosphorylation in smooth muscle cells: induction of cell proliferation and inhibition of celldeath

Objective: The signaling pathways mediating proliferation and apoptosis in vascular smooth muscle cells (VSMC) are not well established It has previou sly been shown that activation of the phosphoinositide 3-OH kinase (PI3K)/A kt pathway or the ERK 1/2 pathway can mediate anti-apoptotic function in di fferent cell types. This study determined the specific contribution of the PI3K/Akt and ERK pathway in the regulation of apoptosis and proliferation o f VSMC. Methods and results: Incubation of rat VSMC with FCS, insulin or IG F-1 time-dependently stimulated the phosphorylation of Akt, however FCS but not insulin or IGF-1 activated the MAP-kinase ERK 1/2. Moreover, insulin i nhibited H2O2-induced apoptosis via the Akt pathway as demonstrated by phar macological inhibition of the PI3K or overexpression of a dominant negative Akt mutant. In contrast, FCS inhibited H2O2-induced apoptosis via the Akt and also the ERK pathway. FCS, but not insulin or IGF-1 induced VSMC prolif eration, suggesting that Akt activation is necessary but not sufficient for VSMC proliferation. FCS-induced proliferation of VSMC was only mediated vi a the Akt pathway and not the ERK pathway. Conclusions: These results defin e a link between cell proliferation and programmed cell death in VSMC via t he same signal transduction pathway, namely activation of the serine/threon ine kinase Akt, which may have significant implication for the development of vascular diseases or remodeling. (C) 2000 Elsevier Science B.V. All righ ts reserved.