The extreme C‐terminal region of phospholipase Cβ1 determines subcellular localization and function; the “b” splice variant mediates α ₁ ‐adrenergic receptor responses in cardiomyocytes

Abstract

Phospholipase Cbeta1 (PLCbeta1) exists as two splice variants, PLCbeta1a (150 kDa) and PLCbeta1b (140 kDa), which differ only in their C-terminal sequences of 64 and 31 amino acids, respectively. The 3 C-terminal amino acid residues of PLCbeta1a comprise a PDZ-interacting domain, whereas the PLCbeta1b sequence has no PDZ-interacting domain but contains unique proline-rich domain 5 residues from the C terminus. PLCbeta1a is localized in the cytoplasm, whereas PLCbeta1b targets to the sarcolemma and is enriched in caveolae. Deletion of 3 amino acids from the C terminus of PLCbeta1b did not alter its sarcolemmal localization, but deletion of the entire unique 31 amino acid sequence caused cytosolic localization. A myristoylated 10 amino acid peptide from the C terminus of PLCbeta1b selectively dissociated N-terminally GFP-tagged PLCbeta1b from the sarcolemma and inhibited PLC responses to alpha(1)-adrenergic agonists, with a half maximal effective concentration of 12 +/- 1.6 microM (mean+/-SE, n=3). A similar peptide from PLCbeta1a was without effect at concentrations below 100 microM. Thus, the extreme C-terminal sequences of the PLCbeta1 splice variants determine localization and, thus, function. In cardiomyocytes, responses initiated by alpha(1)-adrenergic receptor activation involve only PLCbeta1b, and the selective targeting of this splice variant to the sarcolemma provides a potential therapeutic target to reduce hypertrophy, apoptosis, and arrhythmias.