The stimulation of phosphorylation of intracellular proteins in GH₃ rat pituitary tumour cells by phorbol esters of distinct biological activity

Abstract

Using a pituitary tumour cell line (GH3), we have studied the phosphorylation of intracellular proteins induced by phorbol esters of diverse biological activity. All the active phorbol esters, including the weakly tumour-promoting but non-platelet aggregatory compound DOPPA, stimulated the phosphorylation of a cytosolic 80 kDa protein. A protein of this molecular mass has been suggested to be a marker of PKC activity. In contrast, only TPA and the non-tumour promoting but highly active phorbol ester SAP A stimulated the phosphorylation of a 130 kDa membrane protein. The results suggest that these phorbol esters activate PKC, but induce the differential phosphorylation of a variety of intracellular proteins.Protein kinase C; Phorbol ester; Protein phosphorylation

Down-Regulation of Protein Kinase C by Parathyroid Hormone and Mezerein Differentially Modulates cAMP Production and Phosphate Transport in Opossum Kidney Cells

“…However, MEZ‐induced sensitization of cAMP production in OK/E cells is also distinct from the responses produced by PDD in OKwt cells 6 . Although PKC activators can differentially activate or down‐regulate PKC, 8,34–37 MEZ, PDD, and PMA all sensitize cAMP production in OK/E cells, indicating this response is not unique to MEZ. Since these three PKC activators desensitize PTH‐stimulated cAMP production in OKwt cells maintained in our laboratory (unpublished observations), it seems likely that cell‐specific expression of PKC isozymes explains the differences between OK/E and OKwt cells.…”