Induction by melittin of protein phosphorylation in bovine mammary gland and suppression of the phosphorylation by phosphatidylserine.
The protein kinase C (PKC) inhibitor sphingosine induces phosphorylation of an 18-kDa protein in Jurkat T cells and of a 19-kDa protein in bovine mammary gland, and suppresses phosphorylation of substrate proteins for PKC. Melittin, a toxic amphiphilic peptide from bee venom known to inhibit PKC activity, was examined to determine whether it, like sphingosine, induced phosphorylation of the 19-kDa protein. Melittin inhibited PKC activity in both cytosolic and total particulate fractions of bovine mammary gland, with IC50 values (concentrations causing 50% inhibition) of 5-7 microM. Melittin suppressed phosphorylation of such PKC substrate proteins as a 91-kDa protein in cytosol and a 36-kDa protein in the particulate fraction. Besides the suppression, melittin induced phosphorylation of cytosolic 105-kDa, 94-kDa, 27-kDa, 24-kDa and 19-kDa and particulate 110-kDa, 53-kDa and 43-kDa proteins, which were not clearly observed in the absence of melittin. The induction could be detected at a 10 microM concentration. Phosphorylation of these proteins was reversed by excess addition of the PKC cofactor phosphatidylserine, but not by other cofactors such as 1-oleoyl-2-acetyl-sn-glycerol or Ca2+. PKC inhibitors other than melittin [1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine, gossypol, palmitoylcarnitine and adriamycin] had little effect on the induction, except at a high concentration (500 microM) of adriamycin. These results suggest that melittin, like sphingosine, has both suppressive and stimulatory effects on protein phosphorylation in bovine mammary gland.
Katoh
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National Institute of Animal Health, Hokkaido Branch Laboratory, Sapporo, Japan.
D000818:Animals; D001345:Autoradiography; D002417:Cattle; D003600:Cytosol / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D008321:Mammary Glands, Animal / Q000187:drug effects* / Q000378:metabolism*; D008555:Melitten / Q000494:pharmacology*; D010718:Phosphatidylserines / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors* / Q000378:metabolism
D010718:Phosphatidylserines; D008555:Melitten; D011493:Protein Kinase C