Protein kinase C isoforms in human erythrocytes.

Erythrocytes are the most abundant cells in blood and carry out the vital function of oxygen transport. These cells lack nuclei and do not synthesise new proteins. Their cellular responses are modulated entirely by post-translational modifications in existing proteins. Phosphorylation mediated by protein kinase C (PKC) plays a significant role in red cell physiology. To date PKC alpha and zeta are the only isoforms reported to be expressed in erythrocytes. Upon activation they influence cytoskeletal integrity and erythrocyte functions. In this study we report for the first time the presence of PKC iota and PKC mu in addition to PKC alpha and zeta in human erythrocytes. All isoforms were present only in the cytosolic fraction. PKC alpha was the only isoform that translocated to the membrane upon stimulation with phorbol myristate acetate (PMA). It could thus mediate several of the reported PMA-regulated membrane modifications. Investigations on alterations in PMA-mediated phosphorylation of erythrocyte skeletal components in disorders such as chronic myeloid leukaemia can now focus on PKC alpha, which is the only isoform in erythrocytes, which translocates to the membrane on stimulation of the cells.