Herbimycin A inhibits protein kinase C in vascular smooth muscle cells.

It has been observed that in growth arrested vascular smooth muscle cells herbimycin A treatment completely inhibits the activation of mitogen activated protein kinase induced by phorbol 12-myristate 13-acetate (a phorbol ester). Since herbimycin A is a tyrosine kinase inhibitor, this finding raised the possibility of protein kinase C inhibition or down regulation by this compound. Herbimycin A significantly inhibited phorbol myristate acetate-mediated protein kinase C activation as measured by in situ glycogen synthase (GS) peptide and neurogranin peptide phosphorylation in vascular smooth muscle cells. Basal protein kinase activity, i.e. kinase activity without phorbol ester treatment to vascular smooth muscle cells, was also decreased by the treatment of herbimycin A. These findings suggest that herbimycin A also inhibits protein kinase C in vascular smooth muscle cells.