Endogenous Rb protein expression during terminal erythroid differentiation.

Steady state levels and the phosphorylation status of Rb protein were determined by immunoblot analysis of whole cell lysates from FVA erythroblasts cultured with or without EPO for the indicated times. Known Rb− (MB436) and Rb+ (Molt 4) cell lines were included as controls. Equal amounts of protein were electrophoretically separated in a 7% polyacrylamide gel, transferred to nitrocellulose, and immunoblotted with anti-Rb. Positions of hyperphosphorylated (ppRb) and hypophosphorylated (pRb) Rb are indicated. gp55 protein expression is shown as a control for protein loading.