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Abstract
Macrophage cells in different organs, such as microglia and alveolar macrophages, maintain normal organ homeostasis and become activated in response to injury and infection. Under acute activation conditions, they play an important role in phagocytosing dead cells. However, sustained activation of macrophages leads to an overproduction of inflammatory mediators, resulting in persistent inflammatory responses and inflammatory diseases. Regulator of G-protein signaling 10 (RGS10) is a small member of the R12/D RGS subfamily, which canonically modulates G-protein signaling through its GTPase-activating protein (GAP) activity. RGS10 has an abundant expression in resting microglia and macrophages, but its expression is suppressed following LPS stimulation. In the first study, we aimed to determine the inflammatory responses required for LPS-induced RGS10 suppression. Our data show that pharmacological inhibition of PI3K activity, NF-κB-dependent TNF-α and HDAC (1-3) activities stabilize RGS10 expression following LPS stimulation in alveolar macrophages, microglia and BMDMs, suggesting that these inflammatory mediators facilitate the suppressive effect of LPS on RGS10 expression. Independent of its GAP function, RGS10 acts as an anti-inflammatory protein by inhibiting LPS-induced proinflammatory mediators, such as TNF-α and COX-2. In the second study, our goal was to identify non-canonical binding partners of RGS10 in microglia and their possible roles in mediating its anti-inflammatory effects. Among multiple interacting proteins, we identify stromal interaction molecule (STIM2) as a novel binding partner of RGS10 in BV2 microglia cells and RAW264.7 macrophage cells. Further, we demonstrate that STIM2-Orai activity is a downstream signaling pathway of TLR4 activation-stimulated COX-2, and it is essential for RGS10 action on LPS-stimulated COX-2 and TNF-α. Due to the ability of microglial RGS10 to suppress inflammatory signaling in GAP-independent mechanism, the third aim of our study was to determine whether RGS10 regulates inflammatory signaling in ovarian cancer, and if so, whether this effect is mediated by enhanced Gαi signaling. Our data show that loss of RGS10 significantly amplifies NF-κB-p65 phosphorylation, TNF-α and COX-2 transcripts in SKOV3 cells, and upregulation of inflammatory signaling mediated by RGS10 knockdown is not affected by Gαi inhibition. The findings of our study provide novel insights into both the mechanism controlling RGS10 expression and the mechanism underlying RGS10’s anti-inflammatory function in activated microglia and macrophages.