Epo signaling is functional in endothelial cells but not in SMCs. Analysis of mRNA expression of EpoR (A) and βCR (B) in TF-1 cells, HUVECS, and SMCs was performed by semiquantitative RT-PCR. Normalized expression levels of TF-1 cells were set to 1. Mean and SD of 2 independent experiments are shown. (C) Effect of Epo and VEGF on phosphorylation of Stat5, JAK2, and ERK1/2, Akt, and p38 MAPK in HUVECs (C) and SMCs (D) was analyzed by Western blotting with phospho-specific antibodies. Serum-starved cells were stimulated for 15 minutes with VEGF (C), different doses of Epo (C-D), or 10% fetal calf serum (D). As a control for equal protein loading, membranes were reprobed with antibodies against α-tubulin. The intensity of the bands in panel C was quantitatively analyzed as indicated in the right panel (expressed in arbitrary units).