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-contain ing proteins was altered. Upon induction the overall level of phosphot yrosine-containing proteins increased. To examine the role of protein phosphorylation in HD3 cells differentiation, the cells were treated w ith specific inhibitors. In the presence of okadaic acid, cell prolife ration was arrested and accompanied by a marked increase in haemoglobi n synthesis, a differentiation marker of erythroid cells. Okadaic acid caused decrease of the phosphotyrosine-containing proteins, presumabl y to maintain a balance between phosphorylation/dephosphorylation proc esses in the cells. Addition of 3-isobutyl-1-methyl-xanthine, an activ ator 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 sp ecific inhibitor of phosphotyrosine phosphatase, increased the level o f phosphotyrosine proteins and induced differentiation of HD3 cells. T hese results indicate that phosphorylation of cellular proteins is cou pled with a reaction(s) which is responsible for triggering the differ entiation of HD3 cells. The phosphorylation/dephosphorylation processe s are associated with an early event(s) during the differentiation of HD3 cells and may not be connected to tyrosine residues. (C) 1998 John Wiley & Sons, Ltd.