Cloning of a splice variant of rat Phospholipase C-beta4 which is not activated by Gaq

Previously reported the cloning of a cDNA encoding rat phospholipase C-b4 (PLC-b4), a mammalian homolog of Drosophila NorpA PLC (Kim, M.J., Bahk, Y.Y., Min, 1).S., Lee, S.-J., Ryu, S.H., and Sub, P.-G. (1993) Biochem. Biophys. Res. Commun. 194,706-712). We now report the isolation of a splice variant (PLC-b4b). PLC-b4b is identical to the 130 kDa PLC-b4 (PLC-b4a) except that the carboxyl-terminal 162 amino acids of PLC-b4a are replaced with 10 distinct amino acids. The existence of PLC-b4b transcripts in the rat brain was dernonstrated by RT-PCR analysis. Immunological -analysis using polyclonal antibody specific for PLC-b4b revealed that this splice variant exists in the rat brain cytosol. To investigate functional differences between the two forms of PLC-b4, transient expression studies in COS-7 cells were conducted. We found that PLC-b4a is mainly localized in the particulate fraction of the cell and can be activated by Gaq, whereas PLC-b4b is exclusively localized in the soluble fraction and can not be activated by Gaq. In addition both PLC-b4a and PLC-b4b were not activated by G-protein bg-subunits purified from rat brain. These results suggest that the carboxyl-terminal 162 amino acids of PLC-b4a might be required for association of the protein with the particulate fraction and activation by Gaq and suggest that PLC-b4b may be regulated by a different mechanism and play a distinct role in PLC-mediated signal transduction.