A naturally occurring membrane-anchored Gα(s) variant, XLα(s), activates phospholipase Cβ4

Extra-large stimulatory Gα (XLα(s)) is a large variant of G protein α(s) subunit (Gα(s)) that uses an alternative promoter and thus differs from Gα(s) at the first exon. XLα(s) activation by G protein–coupled receptors mediates cAMP generation, similarly to Gα(s); however, Gα(s) and XLα(s) have been shown to have distinct cellular and physiological functions. For example, previous work suggests that XLα(s) can stimulate inositol phosphate production in renal proximal tubules and thereby regulate serum phosphate levels. In this study, we show that XLα(s) directly and specifically stimulates a specific isoform of phospholipase Cβ (PLCβ), PLCβ4, both in transfected cells and with purified protein components. We demonstrate that neither the ability of XLα(s) to activate cAMP generation nor the canonical G protein switch II regions are required for PLCβ stimulation. Furthermore, this activation is nucleotide independent but is inhibited by Gβγ, suggesting a mechanism of activation that relies on Gβγ subunit dissociation. Surprisingly, our results indicate that enhanced membrane targeting of XLα(s) relative to Gα(s) confers the ability to activate PLCβ4. We also show that PLCβ4 is required for isoproterenol-induced inositol phosphate accumulation in osteocyte-like Ocy454 cells. Taken together, we demonstrate a novel mechanism for activation of phosphoinositide turnover downstream of G(s)-coupled receptors that may have a critical role in endocrine physiology.