EFFECT OF TUMOR-PROMOTING AGENTS ON PROTEIN-PHOSPHORYLATION IN HUMAN PLACENTA

1. The effects of okadaic acid (OA) and phorbol-12-myristate-13-acetat e (PMA) on protein phosphorylation were studied in human term placenta s. 2. When samples treated with tumour promoters were compared with un treated samples, the phosphorylation of a 135 kDa protein was signific antly decreased; OA also produced a decrease in phosphorylation of a 2 4 kDa protein. 3. Both substances produced an alteration in the propor tions of bands of masses 170, 65 and 24 kDa, relative to total phospho rylation; PMA treatment also affected the band of mass 135 kDa. 4. Pla cental cell extracts were also subjected to Western blotting with a pr otein kinase C (PKC) antibody, reportedly specific for the alpha- and beta-isoforms. 5. Two immunoreactive proteins were detected; an 80 kDa band, presumably corresponding to the alpha- or beta-PKC, and a 64 kD a protein, which could be a degradation production of the 80 kDa prote in or it could correspond to another form of the enzyme. The expressio n of PKC did not change on treatment with PMA.