Calpain Inhibitors Block Tpa-Dependent Down-Regulation of Protein Kinase C

In vivo involvement of calpain in down-regulation of protein kinase C (PK-C) was studied in a neuroblastoma cell-line, BIM. Treatment of BIM cells with l2-O-tetradecanoylphorbol 13-acetate (TPA) caused down-regulation of PK-C. Introduction of functional calpastatin peptide and inhibitors against calpain blocked TPAdependent down-regulation of PK-C, while a control peptide and the other inhibitors had no effect. The results suggest in vivo involvement of calpain in downregulation of PK-C during signal transduction.