A cytosolic, Gα(q)- and βγ-insensitive splice variant of phospholipase C-β4

Abstract

Phospholipase C (PLC)-β4 has been considered to be a mammalian homolog of the NorpA PLC, which is responsible for visual signal transduction in Drosophila. We reported previously the cloning of a cDNA encoding rat phospholipase C-β4 (PLC-β4) (Kim, M.J., Bahk, Y.Y., Min, D. S., Lee, S.J., Ryu, S.H., and Suh, P.-G. (1993) Biochem. Biophys. Res. Commun. 194, 706- 712). We re- port now the isolation and characterization of a splice variant (PLC-β4b). PLC-β4b is identical to the 130-kDa PLC-β4 (PLC-β4a) except that the carboxyl-terminal 162 amino acids of PLC-β4a are replaced by 10 distinct amino acids. The existence of PLC-β4b transcripts in the rat brain was demonstrated by reverse transcription-polymerase chain reaction analysis. Immunological analysis using polyclonal antibody specific for PLC-β4b revealed that this splice variant exists in rat brain cytosol. To investigate functional differences between the two forms of PLC-β4, transient expression studies in COS-7 cells were conducted. We found that PLC-β4a was localized mainly in the particulate fraction of the cell, and it could be activated by Gα(q), whereas PLC-β4b was localized exclusively in the soluble fraction, and it could not be activated by Gα(q). In addition, both PLC-β4a and PLC- β4b were not activated by G-protein βγ-subunits purified from rat brain. These results suggest that PLC-β4b may be regulated by a mechanism different from that of PLC-β4a, and therefore it may play a distinct role in PLC- mediated signal transduction.