The protein kinase C isoforms leading to MAP-kinase activation in CHO cells.

Stimulation of CHO cells with phorbol ester caused transient activation of mitogen-activated protein kinase (MAP-kinases with 42 and 44 kDa). A similar treatment of CHO cells which overexpress a massive amount of the alpha- or delta-isoform of protein kinase C (PKC) resulted in the prolonged activation of MAP-kinase and eventually in the appearance of mostly dikaryotic, sometimes tetrakaryotic cells. The results suggest that the delta-isoform, as well as the alpha-isoform, has a potential to cause MAP kinase activation. Unusual activation of the PKC/MAP-kinase pathway, however, may lead to abnormal cytokinesis.