RGS21, a regulator of taste and mucociliary clearance?

Regulator of G protein signaling 12 drives inflammatory arthritis by activating synovial fibroblasts through MYCBP2/KIF2A signaling

Synovial fibroblasts are the active and aggressive drivers in the progression of arthritis, but the cellular and molecular mechanisms remain unknown. Here, our results showed that regulator of G protein signaling 12 (RGS12) maintained ciliogenesis in synovial fibroblasts, which is critical for the development of inflammatory arthritis. Deletion of RGS12 led to a significant decrease in ciliogenesis, adhesion, migration, and secretion of synovial fibroblasts. Mechanistically, RGS12 overexpression in synovial fibroblasts increased the length and number of cilia but decreased the protein level of kinesin family member 2A (KIF2A). The results of LC-MS analyses showed that RGS12 interacted with MYC binding protein 2 to enhance its ubiquitination activity, through which the KIF2A protein was degraded in synovial fibroblasts. Moreover, overexpression of KIF2A blocked the increases in cilia length and number. Mice with RGS12 deficiency or treatment of RGS12 shRNA nanoparticles significantly decreased the clinical score, paw swelling, synovitis, and cartilage destruction during inflammatory arthritis by inhibiting the activation of synovial fibroblasts. Therefore, this study provides evidence that RGS12 activates synovial fibroblasts' pathological function via promoting MCYBP2-mediated degradation of KIF2A and ciliogenesis. Our data suggest that RGS12 may be a potential drug target for the treatment of inflammatory arthritis.

The stability of tastant detection by mouse lingual chemosensory tissue requires Regulator of G protein Signaling-21 (RGS21)

The T1R and T2R families of G protein-coupled receptors (GPCRs) initiate tastant perception by signaling via guanine nucleotide exchange and hydrolysis performed by associated heterotrimeric G proteins (Gαβγ). Heterotrimeric G protein signal termination is sped up by Gα-directed GTPase-accelerating proteins (GAPs) known as the Regulators of G protein Signaling (RGS proteins). Of this family, RGS21 is highly expressed in lingual epithelial cells and we have shown it acting in vitro to decrease the potency of bitterants on cultured cells. However, constitutive RGS21 loss in mice reduces organismal response to GPCR-mediated tastants-opposite to expectations arising from observed in vitro activity of RGS21 as a GAP and inhibitor of T2R signaling. Here, we show reduced quinine aversion and reduced sucrose preference by mice lacking RGS21 does not result from post-ingestive effects, as taste-salient brief-access tests confirm the reduced bitterant aversion and reduced sweetener preference seen using two-bottle choice testing. Eliminating Rgs21 expression after chemosensory system development, via tamoxifen-induced Cre recombination in eight week-old mice, led to a reduction in quinine aversive behavior that advanced over time, suggesting that RGS21 functions as a negative regulator to sustain stable bitter tastant reception. Consistent with this notion, we observed downregulation of multiple T2R proteins in the lingual tissue of Rgs21-deficient mice. Reduced tastant-mediated responses exhibited by mice lacking Rgs21 expression either since birth or in adulthood has highlighted the potential requirement for a GPCR GAP to maintain the full character of tastant signaling, likely at the level of mitigating receptor downregulation.

Single Nucleotide Polymorphisms in Chemosensory Pathway Genes GNB3, TAS2R19, and TAS2R38 Are Associated with Chronic Rhinosinusitis

BACKGROUND

Chronic rhinosinusitis (CRS) is a multifaceted disease with a significant genetic component. The importance of taste receptor signaling has recently been highlighted in CRS; single nucleotide polymorphisms (SNPs) of bitter tastant-responsive G-protein-coupled receptors have been linked with CRS and with altered innate immune responses to multiple bacterially derived signals.

OBJECTIVE

To determine in CRS the frequency of six SNPs in genes with known bitter tastant signaling function.

METHODS

Genomic DNA was isolated from 74 CRS volunteers in West Virginia, and allele frequency was determined and compared with demographically matched data from the 1,000 Genomes database.

RESULTS

For two SNPs in a gene recently associated with bitterant signaling regulation, RGS21, there were no associations with CRS (although the frequency of the minor allele of RGS21, rs7528947, was seen to increase with increasing Lund-Mackay CT staging score). Two TAS2R bitter taste receptor gene variants (TAS2R19 rs10772420 and TAS2R38 rs713598), identified in prior CRS genetics studies, were found to have similar associations in this study.

CONCLUSION

Unique to our study is the establishment of an association between CRS in this patient population and GNB3 SNP rs5443, a variation in an established G protein component downstream of bitterant receptor signal transduction.

Development of Full Sweet, Umami, and Bitter Taste Responsiveness Requires Regulator of G protein Signaling-21 (RGS21)

The mammalian tastes of sweet, umami, and bitter are initiated by activation of G protein-coupled receptors (GPCRs) of the T1R and T2R families on taste receptor cells. GPCRs signal via nucleotide exchange and hydrolysis, the latter hastened by GTPase-accelerating proteins (GAPs) that include the Regulators of G protein Signaling (RGS) protein family. We previously reported that RGS21, uniquely expressed in Type II taste receptor cells, decreases the potency of bitter-stimulated T2R signaling in cultured cells, consistent with its in vitro GAP activity. However, the role of RGS21 in organismal responses to GPCR-mediated tastants was not established. Here, we characterized mice lacking the Rgs21 fifth exon. Eliminating Rgs21 expression had no effect on body mass accumulation (a measure of alimentation), fungiform papillae number and morphology, circumvallate papillae morphology, and taste bud number. Two-bottle preference tests, however, revealed that Rgs21-null mice have blunted aversion to quinine and denatonium, and blunted preference for monosodium glutamate, the sweeteners sucrose and SC45647, and (surprisingly) NaCl. Observed reductions in GPCR-mediated tastant responses upon Rgs21 loss are opposite to original expectations, given that loss of RGS21-a GPCR signaling negative regulator-should lead to increased responsiveness to tastant-mediated GPCR signaling (all else being equal). Yet, reduced organismal tastant responses are consistent with observations of reduced chorda tympani nerve recordings in Rgs21-null mice. Reduced tastant-mediated responses and behaviors exhibited by adult mice lacking Rgs21 expression since birth have thus revealed an underappreciated requirement for a GPCR GAP to establish the full character of tastant signaling.

R4 Regulator of G Protein Signaling (RGS) Proteins in Inflammation and Immunity

G protein-coupled receptors (GPCRs) have important functions in both innate and adaptive immunity, with the capacity to bridge interactions between the two arms of the host responses to pathogens through direct recognition of secreted microbial products or the by-products of host cells damaged by pathogen exposure. In the mid-1990s, a large group of intracellular proteins was discovered, the regulator of G protein signaling (RGS) family, whose main, but not exclusive, function appears to be to constrain the intensity and duration of GPCR signaling. The R4/B subfamily--the focus of this review--includes RGS1-5, 8, 13, 16, 18, and 21, which are the smallest RGS proteins in size, with the exception of RGS3. Prominent roles in the trafficking of B and T lymphocytes and macrophages have been described for RGS1, RGS13, and RGS16, while RGS18 appears to control platelet and osteoclast functions. Additional G protein independent functions of RGS13 have been uncovered in gene expression in B lymphocytes and mast cell-mediated allergic reactions. In this review, we discuss potential physiological roles of this RGS protein subfamily, primarily in leukocytes having central roles in immune and inflammatory responses. We also discuss approaches to target RGS proteins therapeutically, which represents a virtually untapped strategy to combat exaggerated immune responses leading to inflammation.

Regulators of G-protein-signaling proteins: negative modulators of G-protein-coupled receptor signaling

Regulators of G-protein-signaling (RGS) proteins are a category of intracellular proteins that have an inhibitory effect on the intracellular signaling produced by G-protein-coupled receptors (GPCRs). RGS along with RGS-like proteins switch on through direct contact G-alpha subunits providing a variety of intracellular functions through intracellular signaling. RGS proteins have a common RGS domain that binds to G alpha. RGS proteins accelerate GTPase and thus enhance guanosine triphosphate hydrolysis through the alpha subunit of heterotrimeric G proteins. As a result, they inactivate the G protein and quickly turn off GPCR signaling thus terminating the resulting downstream signals. Activity and subcellular localization of RGS proteins can be changed through covalent molecular changes to the enzyme, differential gene splicing, and processing of the protein. Other roles of RGS proteins have shown them to not be solely committed to being inhibitors but behave more as modulators and integrators of signaling. RGS proteins modulate the duration and kinetics of slow calcium oscillations and rapid phototransduction and ion signaling events. In other cases, RGS proteins integrate G proteins with signaling pathways linked to such diverse cellular responses as cell growth and differentiation, cell motility, and intracellular trafficking. Human and animal studies have revealed that RGS proteins play a vital role in physiology and can be ideal targets for diseases such as those related to addiction where receptor signaling seems continuously switched on.