Calmodulin is a phospholipase C-β interacting protein

Phospholipase C-beta(3) (PLCbeta(3)) is an important effector enzyme in G protein-coupled signaling pathways. Activation of PLCbeta(3) by Galpha and Gbetagamma subunits has been fairly well characterized, but little is known about other protein interactions that may also regulate PLCbeta(3) function. A yeast two-hybrid screen of a mouse brain cDNA library with the amino terminus of PLCbeta(3) has yielded potential PLCbeta(3) interacting proteins including calmodulin (CaM). Physical interaction between CaM and PLCbeta(3) is supported by a positive secondary screen in yeast and the identification of a CaM binding site in the amino terminus of PLCbeta(3). Co-precipitation of in vitro translated and transcribed amino- and carboxyl-terminal PLCbeta(3) revealed CaM binding at a putative amino-terminal binding site. Direct physical interaction of PLCbeta(3) and PLCbeta(1) isoforms with CaM is supported by pull-down of both isoenzymes with CaM-Sepharose beads from 1321N1 cell lysates. CaM inhibitors reduced M1-muscarinic receptor stimulation of inositol phospholipid hydrolysis in 1321N1 astrocytoma cells consistent with a physiologic role for CaM in modulation of PLCbeta activity. There was no effect of CaM kinase II inhibitors, KN-93 and KN-62, on M1-muscarinic receptor stimulation of inositol phosphate hydrolysis, consistent with a direct interaction between PLCbeta isoforms and CaM.