ERK1/2 is involved in the overactivation of mTORC1 and S6K by pathophysiologic albumin concentrations. Modulation by 10 μm U0126, a specific MEK inhibitor, of the effect of albumin (alb) on mTOR phosphorylation at Ser-2448 (A); mTORC1 activity by S6K phosphorylation at Thr-389 (B); S6K phosphorylation at Thr-389, Ser-371, Thr-421, and Ser-424 (C); PRAS40 phosphorylation at Ser-183 (D); and TSC2 phosphorylation of the serine (S) residue located at the PXSP motif, induced by albumin (E). F, time course of the effect of albumin on the phosphorylation of TSC2 at Ser-664 (n = 8). The results are shown as means ± S.E. *, p < 0.05 versus control; #, p < 0.05 versus 20.0 mg/ml albumin. 1′, 1 min.