Alternative splice variants of phospholipase C-β2 are expressed in platelets: Effect on Gαq-dependent activation and localization

Abstract

Phospholipase C (PLC) β2 plays a pivotal role in G-protein dependent signal transduction in platelets. We have previously demonstrated in platelets, leukocytes and human erythroleukemia cells the presence of transcripts of two forms of PLC-β2 generated by alternative splicing. They differ by 45 nucleotides in the carboxyl-terminal region and are designated as PLC-β2a and PLC-β2b, with and without by 15 amino acid residues (corresponding to 864–878). The presence of the two variants has not been shown at the protein level in cells. Moreover, the carboxy-terminal region of PLC-β has been implicated in Gαq activation, particulate association, and nuclear localization, suggesting that the PLC-β2 splice variants may be regulated differentially. We demonstrate for the first time that both PLC-β2 isoforms are expressed in platelets at the protein level. Studies in CV-1 cells transfected with PLC-β2a or β2b cDNAs, along with constitutively activated Gαq (Q209L), showed that inositolphosphate formation was comparable between the two variants. However, the nuclear localization of the two isoforms was different with a higher cytoplasmic to nuclear ratio for PLC-β2b compared to PLC-β2a, suggesting that a great proportion of the total PLC-β2a was in the nucleus relative to PLC-β2b. There was no difference in the relative distribution of the two variants between the cytosol and particulate fractions. Both PLC-β2 alternative splice variants are expressed at the protein level in platelets. In transfected CV-1 cells, PLC-β2a is relatively more enriched in the nuclei than PLC-β2b suggesting that the two variants may have different effects in cell proliferation and differentiation.