PROTEIN-KINASE-C ISOTYPES IN HUMAN ERYTHROLEUKEMIA (K562) CELL-PROLIFERATION AND DIFFERENTIATION - EVIDENCE THAT BETA-II PROTEIN-KINASE-C IS REQUIRED FOR PROLIFERATION

The human erythroleukemia (K562) cell line undergoes megakaryocytic di fferentiation and cessation of proliferation when treated with phorbol myristate acetate (PMA). To investigate the role of individual protei n kinase C (PKC) isotypes in these events, we have assessed PKC isotyp e expression during leukemic proliferation and PMA-induced differentia tion. Immunoblot analysis using isotype-specific antibodies demonstrat es that proliferating K562 cells express the alpha, beta(II), and zeta PKC isotypes. PMA-induced differentiation and cytostasis lead to a de crease in beta(II) PKC and increases in alpha and zeta PKC levels. The role of the alpha and beta(II), PKC isotypes was further assessed in cells overexpressing these isotypes. K562 cells overexpressing human a lpha PKC grew more slowly and were more sensitive to the cytostatic ef fects of PMA than control cells, whereas cells overexpressing beta(II) PKC were less sensitive to PMA. PMA-induced cytostasis is reversed up on removal of PMA. Resumption of proliferation is accompanied by reexp ression of beta(II) PKC to near control levels, whereas alpha and zeta PKC levels remain elevated for several days after removal of PMA. Pro liferation of PMA-withdrawn cells can be partially inhibited by antise nse beta(II), PKC oligodeoxyribonucleotide. Growth inhibition is dose- dependent, specific for beta(II) PKC-directed antisense oligonucleotid e, and associated with significant inhibition of beta(II) PKC levels i ndicating that beta(II) PKC is essential for K562 cell proliferation. Sodium butyrate, which unlike PMA induces megakaryocytic differentiati on without cytostasis, causes increases in both alpha and beta(II) PKC levels. These data demonstrate that beta(II) PKC is required for K562 cell proliferation, whereas alpha PKC is involved in megakaryocytic d ifferentiation.