Calmodulin is a phospholipase C-beta interacting protein

Abstract

Phospholipase C-beta 3 (PLC beta 3) is an important effector enzyme in G protein-coupled signaling pathways. Activation of PLC beta 3 by G alpha and G beta gamma subunits has been fairly well characterized, but little is known about other protein interactions that may also regulate PLC beta 3 function. A yeast two-hybrid screen of a mouse brain cDNA library with the amino terminus of PLC beta 3 has yielded potential PLC beta 3 interacting proteins including calmodulin (CaM). Physical interaction between CaM and PLC beta 3 is supported by a positive secondary screen in yeast and the identification of a CaM binding site in the amino terminus of PLC beta 3. Co-precipitation of in vitro translated and transcribed amino- and carboxyl-terminal PLC beta 3 revealed CaM binding at a putative amino-terminal binding site. Direct physical interaction of PLC beta 3 and PLC beta 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 PLC beta 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 PLC beta isoforms and CaM.