Selective Targeting of a PKC Isozyme

Abstract

Maeno-Hikichi et al. investigated protein kinase C (PKC) regulation of Ca 2+ channels and discovered an adaptor protein that targeted PKCε to N-type Ca 2+ channels to form a functional signaling complex. At least 10 isozymes of PKC, a family of cytosolic kinases that translocate to the membrane after activation by diacylglycerol, are found in neurons. Although individual PKC isozymes are believed to mediate unique functions, the mechanisms underlying their specificity of action remain unclear. Maeno-Hikichi et al. used yeast two-hybrid screening of rat brain cDNA libraries to identify proteins that interacted with N-type but not P/Q-type Ca 2+ channels and cloned enigma homolog (ENH), a protein known to bind PKC in vitro. Immunostaining revealed ENH expression in various brain regions and demonstrated that ENH was located in both neuronal cell bodies and presynaptic nerve terminals. The authors combined immunoprecipitation with Western analysis to demonstrate a PKCε-ENH-N-type Ca 2+ channel complex. When coexpressed with Ca 2+ channels in Xenopus oocytes, ENH facilitated PKC modulation of current through N-type but not P/Q-type Ca 2+ channels; expression of chimeric channels confirmed that this facilitation of Ca 2+ current depended on the Ca 2+ channel's ENH-binding region. Disruption of the macromolecular complex with a peptide that inhibited PKCε translocation inhibited PKC facilitation of N-type Ca 2+ current in hippocampal neurons. Thus, ENH is able to target a specific PKC isoform to a specific substrate, permitting selective modulation of Ca 2+ current through a particular class of channels. Y. Maeno-Hikichi, S. Chang, K. Matsumura, M. Lai, H. Lin, N. Nakagawa, S. Kuroda, J.-F. Zhang, A PKCε-ENH-channel complex specifically modulates N-type Ca 2+ channels. Nat. Neurosci . 6 , 468-475 (2003). [Online Journal]