RGS10 regulates the expression of Cyclooxygenase-2 and Tumor Necrosis Factor alpha through a G-protein-independent mechanism

Regulator of G protein signaling (RGS) proteins classically act as negative regulators of heterotrimeric G proteins to terminate signaling initiated by G protein coupled receptors, allowing RGS proteins to play critical roles in the physiology and pathology of diverse systems. However, many studies report RGS protein functions that are independent of G protein regulation. The small RGS protein RGS10 is a key regulator of neuroinflammation and ovarian cancer cell survival; however, the mechanism for RGS10 function in these cells is unknown and has not been linked to any specific G protein pathways. RGS10 is highly enriched in microglia, and loss of RGS10 expression in microglia amplifies production of the inflammatory cytokine TNFα and enhances microglia-induced neurotoxicity. Similarly, RGS10 regulates cell survival and chemoresistance of ovarian cancer cells through an unknown mechanism. Cyclooxygenase-2 (COX-2) mediated production of prostaglandins such as PGE2 is a key factor in both inflammation and cancer chemoresistance, suggesting it may be involved in RGS10 function in both cell types, but a connection between RGS10 and COX-2 has not been reported. To address these questions, we completed a mechanistic study to characterize RGS10 regulation of TNFα and COX-2 and to determine if these effects are mediated through a G protein dependent mechanism. Our data show for the first time that loss of RGS10 expression significantly elevates lipopolysaccharide-stimulated COX-2 expression and release of PGE2 from microglia. Furthermore, the elevated inflammatory signaling resulting from RGS10 loss was not affected by Gαi inhibition, and a RGS10 mutant that is unable to bind activated G proteins was as effective in inhibiting TNFα expression as wild type RGS10. We also show for the first time that RGS10 regulates TNFα and COX-2 inflammatory signaling in ovarian cancer cells through a G protein independent mechanism. Together, our data strongly indicate that RGS10 inhibits COX-2 expression by a G protein independent mechanism to regulate inflammatory signaling in microglia and cancer cells. Identification of this novel mechanism will facilitate strategic targeting of RGS10 to develop new anti-inflammatory therapeutics.