Biosynthesis and posttranslational modifications of protein kinase C in human breast cancer cells.

摘要: Abstract Several forms of protein kinase C with molecular masses 74-, 77-, and 80-kDa were detected in subcellular fractions human breast cancer MDA-MB-231 cells which express the alpha-type C. lines evidence indicated that 74-kDa is precursor 77- forms. (i) Pulse-labeling experiments revealed synthesized on membranes as a can be chased into (ii) The primary translation product displayed an apparent size determined by vitro poly(A)+ RNA from cells. (iii) Incubation serine/threonine-specific phosphatases (potato acid phosphatase 1 or 2A) resulted complete dephosphorylation 77-kDa to form. Protein appears unphosphorylated presumably inactive form converted active post-translational modification involving at least two phosphorylation steps. first probably achieved specific, yet unidentified, "protein kinase" since species did not undergo autophosphorylation was neither substrate for purified C, S6 kinase, phosphorylase casein II, nor catalytic subunit cAMP-dependent kinase. Except (autophosphorylation), II shifted mass 80-kDa. Prolonged exposure phorbol 12-myristate 13-acetate only leads down-regulation activity but also accumulation due retarded conversion these Our data indicate tumor promoters additionally interfere posttranslational processing converts enzyme.