Megakaryocytic differentiation of K562 cells is associated with changes in the cytoskeletal organization and the pattern of chromatographically distinct forms of phosphotyrosyl-specific protein phosphatases

Abstract

We have analyzed morphological and biochemical changes occurring during megakaryocytic differentiation of the human chronic myelogenous leukemia cell line K562 induced by phorbol 12-myristate 13-acetate (PMA). PMA-treated cells became growth arrested, were slightly larger and irregular in shape, adhered better to the culture flask surface, and expressed the glycoprotein IIIa on their surfaces. The morphological changes induced by PMA treatment were associated with the disappearance of actin from the cytosol and presumably reflect PMA-induced actin polymerization. Megakaryocytic differentiation was accompanied by about a 3-fold decrease in the specific phosphotyrosine protein phosphatase (PTPase) activity in the particulate membrane fraction, whereas the activity in the soluble cytosol fraction increased about 3-fold. The decrease of PTPase activity in the particulate membrane fraction could be attributed to the disappearance of at least 1 distinct PTPase form displaying an apparent native Mr of 200,000 and a reduction in activity of a Mr 43,000 PTPase found associated with membranes of all cells examined to date. The increase of PTPase activity in the cytosol fraction manifested itself by the appearance of a new Mr 40,000 PTPase and a reduction of a Mr 60,000 PTPase. These results suggest the existence of several growth- and/or differentiation-related PTPase activities in K562 cells.