Phosphatidylinositol 3-kinase is required for growth factor-induced amino acid uptake by vascular smooth muscle cells

Although accumulating evidence suggests that phosphatidylinositol 3-kinase (PI3K) is a common signaling molecule for growth factor-induced amino acid uptake by the cell, the role of PI3K in the uptake of different amino acids was not tested under the same conditions. In this study, we asked whether PI3K mediates platelet-derived growth factor (PDGF) -stimulated uptake of d ifferent amino acids that are taken up through 3 major amino acid transport ers expressed in rat vascular smooth muscle cells and other cell types and whether PI3K mediates amino acid uptake stimulated with different growth fa ctors and vasoactive substances. PDGF increased the uptake of [H-3]leucine, [H-3]proline, and [H-3]arginine in a dose- and time-dependent fashion. Two different PI3K inhibitors, wortmannin (100 nmol/L) and LY294002 (10 mu mol /L), completely inhibited the amino acid uptake stimulated by PDGF. Chinese hamster ovary cells expressing both PDCF receptor-beta and a dominant-nega tive PI3K did not increase their leucine uptake when stimulated with PDGF, whereas the same cells expressing only PDGF receptor-beta did. Transforming growth factor-beta, as well as insulin-like growth factor-I and angiotensi n II, increased leucine uptake by vascular smooth muscle cells. Wortmannin and LY294002 inhibited this increase. We also found that transforming growt h factor-beta stimulated PI3K activity and the phosphorylation of Akt, a do wnstream signaling molecule of PI3K. A similar effect of PI3K inhibitors on amino acid uptake was observed in Swiss 3T3 cells. We conclude that P13K m ediates the uptake of different amino acids by vascular smooth muscle cells and other eel types stimulated with a variety of growth factors, including transforming growth factor-beta, Our findings suggest that PI3K may play a n important role in vascular pathophysiology by regulating amino acid uptak e.