PROTEIN-KINASE-C SUBSTRATES AND GANGLIOSIDE INHIBITORS IN BOVINE MAMMARY NUCLEI

In cow mammary gland, unlike in other tissues, gangliosides (putative physiologic regulators of protein kinase C) may be distributed in nucl ei and on the cell surface. This study was designed to determine wheth er gangliosides and the protein kinase C system (the enzyme and its su bstrate proteins) are present in cow mammary gland nuclei and to exami ne the effect of gangliosides detected in nuclei on protein phosphoryl ation catalyzed by protein kinase C. Gangliosides GM3, GD3, and GT1b w ere detected in the highly purified nuclear fraction. The nuclear gang lioside pattern was different from those of whole tissue and cytosol, thereby suggesting the presence of the gangliosides in nuclei. Protein kinase C and its substrate proteins (120, 97, 56, 43, 38, and 36 kDa) were extracted by Triton X-100 treatment of nuclei. Both protein kina se C activity (histone phosphorylation) and the nuclear substrate phos phorylation were effectively inhibited by the three gangliosides. Of t he gangliosides, GT1b was the most potent in inhibiting phosphorylatio n, followed by GD3 and GM3. These results suggest that signal transduc tion mediated by protein kinase C in cow mammary gland nuclei may be r egulated by gangliosides.