Alteration of phosphotyrosine-containing proteins during differentiation of chicken erythroleukemia cells (HD3).

After treatment of HD3 cells with erythroid-inducing agents (hemin and butyric acid) at 42 degrees C, the profile of phosphotyrosine-containing proteins was altered. Upon induction the overall level of phosphotyrosine-containing proteins increased. To examine the role of protein phosphorylation in HD3 cells differentiation, the cells were treated with specific inhibitors. In the presence of okadaic acid, cell proliferation was arrested and accompanied by a marked increase in haemoglobin synthesis, a differentiation marker of erythroid cells. Okadaic acid caused decrease of the phosphotyrosine-containing proteins, presumably to maintain a balance between phosphorylation/dephosphorylation processes in the cells. Addition of 3-isobutyl-1-methyl-xanthine, an activator of phosphatases, caused a decrease or disappearance of almost all phosphotyrosine-containing proteins and, at the same time, prevented the erythroid differentiation of HD3 cells. Sodium orthovanadate, a specific inhibitor of phosphotyrosine phosphatase, increased the level of phosphotyrosine proteins and induced differentiation of HD3 cells. These results indicate that phosphorylation of cellular proteins is coupled with a reaction(s) which is responsible for triggering the differentiation of HD3 cells. The phosphorylation/dephosphorylation processes are associated with an early event(s) during the differentiation of HD3 cells and may not be connected to tyrosine residues.