PMA produces activation of ERKs, inactivation of JNKs, and inhibition of cell apoptosis. HCD-57 cells were cultured in an EPO-free medium for 4 hours, followed by the addition of 50 nmol/L PMA. Cells were cultured further for the indicated periods of time before either being lysed for Western blot analyses with the indicated antibodies or analyzed for apoptosis. Lane C denotes control cells grown in the presence of EPO.