A cytosolic, Gαq- and βγ-insensitive splice variant of phospholipase C-β4

Phospholipase C (PLC)-beta 4 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-beta 4 (PLC-beta 4) (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 report now the isolation and characterization of a splice variant (PLC-beta 4b). PLC-beta 4b is identical to the 130-kDa PLC-beta 4 (PLC-beta 4a) except that the carboxyl-terminal 162 amino acids of PLC-beta 4a are replaced by 10 distinct amino acids, The existence of PLC-beta 4b transcripts in the rat brain was demonstrated by reverse transcription-polymerase chain reaction analysis. Immunological analysis using polyclonal antibody specific for PLC-beta 4b revealed that this splice variant exists in rat brain cytosol. To investigate functional differences between the two forms of PLC-beta 4, transient expression studies in COS-7 cells were conducted, We found that PLC-beta 4a was localized mainly in the particulate fraction of the cell, and it could be activated by G alpha(q), whereas PLC-beta 4b was localized exclusively in the soluble fraction, and it could not be activated by G alpha(q). In addition, both PLC-beta 4a and PLC-beta 4b were not activated by G-protein beta gamma-subunits purified from rat brain. These results suggest that PLC-beta 4b may be regulated by a mechanism different from that of PLC-beta 4a, and therefore it may play a distinct role in PLC mediated signal transduction.