Western blot analysis of PSer¹³³-CREB and total CREB protein performed in HEL stimulated with agonists inducing differentiation along either the megakaryocytic or erythroid lineages. Cells were either left untreated (negative control, lane 1) or treated for 30 minutes with 10 U/mL Epo (lane 2), 10⁻⁷ mol/L hemin (lane 3), 100 ng/mL TPO (lane 4), 10 μmol/L forskolin (lane 5), or 10⁻⁷ mol/L PMA for 30 minutes (lane 6). Results from one experiment representative of three separate experiments are shown. The densitometric analysis is expressed in arbitrary units (a.u.).