Binding specificity for RACK1 resides in the V5 region of βII protein kinase C

Identification of selective anchoring proteins responsible for specialized localization of specific signaling proteins has led to the identification of new inhibitors of signal transduction, inhibitors of anchoring protein-ligand interactions. RACK1, the first receptor for activated C kinase identified in our lab, is a selective anchoring protein for beta II protein kinase C (beta IIPKC). We previously found that at least part of the RACK1-binding site resides in the C2 domain of beta IIPKC (Ron, D., Luo, J., and Mochly-Rosen, D. (1995) J. Biol. Chem. 270, 24180-24187). Here we show that the V5 domain also contains part of the RACK1-binding site in beta IIPKC. In neonatal rat cardiac myocytes, the beta IIPKC peptide (amino acids 645-650 in beta IIPKC) selectively inhibited phorbol 12-myristate 13-acetate (PMA)-induced translocation of beta IIPKC and not beta IIPKC. In addition, the beta IIV5-3 peptide inhibited cardiac myocyte hypertrophy in PMA-treated cells. Interestingly, beta IV5-3 (646-651 in beta IPKC), a selective translocation inhibitor of beta IPKC, also inhibited PMA-induced cardiac myocyte hypertrophy, demonstrating that both betaI- and beta IIPKC are essential for this cardiac function. Therefore, the beta IIV5 domain contains part of the RACK1-binding site in beta IIPKC; a peptide corresponding to this site is a selective inhibitor of beta IIPKC and, hence, enables the identification of beta IIPKC-selective functions.