Expression of PKC isoforms in human erythroid progenitor cells. Members of all three subfamilies (conventional, novel, atypical) were detected by immunolabeling of cytosolic and membrane proteins with specific monoclonal antibodies. PMA (10 nmol/L, 3 to 10 minutes) induced a translocation of the PKC isoforms , β, γ, δ, ɛ, and θ to the membrane fraction. By contrast, thrombin (2 to 10 U/mL, 3 to 10 minutes) did not affect the subcellular distribution of the enzymes. Apparent membrane association of θ- and ι-kinases may be due to a minor contamination of the particulate fraction with cytosol.