Regulation of Smad-mediated gene transcription by RGS3

Memory Precursors and Short-Lived Effector T cell Subsets Have Different Sensitivities to TGFβ

After exposure to an antigen, CD8 T cells reach a decision point about their fate: to become either short-lived effector cells (SLECs) or memory progenitor effector cells (MPECs). SLECs are specialized in providing an immediate effector function but have a shorter lifespan and lower proliferative capacity compared to MPECs. Upon encountering the cognate antigen during an infection, CD8 T cells rapidly expand and then contract to a level that is maintained for the memory phase after the peak of the response. Studies have shown that the contraction phase is mediated by TGFβ and selectively targets SLECs, while sparing MPECs. The aim of this study is to investigate how the CD8 T cell precursor stage determines TGFβ sensitivity. Our results demonstrate that MPECs and SLECs have differential responses to TGFβ, with SLECs being more sensitive to TGFβ than MPECs. This difference in sensitivity is associated with the levels of TGFβRI and RGS3, and the SLEC-related transcriptional activator T-bet binding to the TGFβRI promoter may provide a molecular basis for increased TGFβ sensitivity in SLECs.

RGS6 suppresses TGF-β-induced epithelial-mesenchymal transition in non-small cell lung cancers via a novel mechanism dependent on its interaction with SMAD4

Regulator of G-protein signaling 6 (RGS6) is a newly discovered tumor suppressor that has been shown to be protective in development of various cancers such as breast cancer and bladder cancer. But the mechanisms underlying these tumor-suppressing functions of RGS6 are not fully understood. Here, we discover a novel function of RGS6 in suppressing TGF-β-induced epithelial-mesenchymal transition (EMT) of non-small cell lung cancer (NSCLC) cells and in vivo NSCLC metastasis. Using both bioinformatics and experimental tools, we showed that RGS6 was downregulated in lung cancer tissues compared to noncancerous counterparts, and low expression of RGS6 was associated with poor survival of lung cancer patients. Overexpression of RGS6 suppressed TGF-β-induced EMT in vitro and TGF-β-promoted metastasis in vivo, by impairing gene expression of downstream effectors induced by the canonical TGF-β-SMAD signaling. The ability of RGS6 to suppress TGF-β-SMAD-mediated gene expression relied on its binding to SMAD4 to prevent complex formation between SMAD4 and SMAD2/3, but independent of its regulation of the G-protein signaling. Interaction between RGS6 and SMAD4 caused less nuclear entry of p-SMAD3 and SMAD4, resulting in inefficient SMAD3-mediated gene expression. Taken together, our findings reveal a novel and noncanonical role of RGS6 in regulation of TGF-β-induced EMT and metastasis of NSCLC and identify RGS6 as a prognostic marker and a potential novel target for NSCLC therapy.

Exploring the expression and preliminary function of chicken regulator of G protein signalling 3 (RGS3) gene in follicular development

1. The following study explored the expression and preliminary function of RGS3. The spatial and temporal expression patterns of the RGS3 gene were analysed in the ovarian stroma of Shendan No. 6 Green shell hens and Hy-line Brown hens at four time points (6, 28, 40 and 52 weeks old), as well as in various organs and follicles of Hy-line Brown hens.2. Based on the genomic and protein sequences of RGS3 in NCBI database, phylogenetic trees were constructed using MEGA-X. The protein interaction network was analysed using STRING. According to the results of protein-protein interaction network and pathways, the mRNA expression levels of RGS3 and three interaction proteins were explored by qRT-PCR in vitro.3. Spatio-temporal expression data revealed that RGS3 mRNA was expressed in all the organs tested, being highest in the hypothalamus. In different follicles, RGS3 mRNA was highly expressed in post-ovulatory follicles, followed by ovarian stroma and large white follicles. The expression levels of RGS3 mRNA in the ovarian stroma were significantly higher in Shendan No. 6 Green shell hens than that in the Hy-line Brown hens at all egg-laying stages.4. The phylogenetic tree results showed that ducks, geese and chickens had higher homology based on the genomic and protein sequence of RGS3. Moreover, chicken RGS3 interacted with GSK3B, RAF1 and BRAF based on STRING prediction. In vitro follicle stimulating hormone (FSH) treatment showed that mRNA expression levels of RGS3 and those of its predicted interacting proteins BRAF and GSK3B decreased with increasing FSH concentration. The results suggested that RGS3 responds to FSH and may play an important role in the regulation follicular development in chicken.

RGS5-TGFβ-Smad2/3 axis switches pro- to anti-apoptotic signaling in tumor-residing pericytes, assisting tumor growth

Regulator-of-G-protein-signaling-5 (RGS5), a pro-apoptotic/anti-proliferative protein, is a signature molecule of tumor-associated pericytes, highly expressed in several cancers, and is associated with tumor growth and poor prognosis. Surprisingly, despite the negative influence of intrinsic RGS5 expression on pericyte survival, RGS5^highpericytes accumulate in progressively growing tumors. However, responsible factor(s) and altered-pathway(s) are yet to report. RGS5 binds with Gαi/q and promotes pericyte apoptosis in vitro, subsequently blocking GPCR-downstream PI3K-AKT signaling leading to Bcl2 downregulation and promotion of PUMA-p53-Bax-mediated mitochondrial damage. However, within tumor microenvironment (TME), TGFβ appeared to limit the cytocidal action of RGS5 in tumor-residing RGS5^highpericytes. We observed that in the presence of high RGS5 concentrations, TGFβ-TGFβR interactions in the tumor-associated pericytes lead to the promotion of pSmad2-RGS5 binding and nuclear trafficking of RGS5, which coordinately suppressed RGS5-Gαi/q and pSmad2/3-Smad4 pairing. The RGS5-TGFβ-pSmad2 axis thus mitigates both RGS5- and TGFβ-dependent cellular apoptosis, resulting in sustained pericyte survival/expansion within the TME by rescuing PI3K-AKT signaling and preventing mitochondrial damage and caspase activation. This study reports a novel mechanism by which TGFβ fortifies and promotes survival of tumor pericytes by switching pro- to anti-apoptotic RGS5 signaling in TME. Understanding this altered RGS5 signaling might prove beneficial in designing future cancer therapy.

RGS3 inhibits TGF-β1/Smad signalling in adventitial fibroblasts

Recent evidence suggests that adventitial fibroblasts (AFs) are crucially implicated in atherosclerosis. However, the mechanisms by which AFs are dysfunctional and contribute to atherosclerosis remain unclear. This study aimed to investigate the role of regulator of G-protein signalling 3 (RGS3) in the regulation of AFs using apoE knockout mouse as the model. Pathological changes in aortic arteries of apoE knockout mice fed with hyperlipid diet were examined by Movat staining. The expression of RGS3, α-SMA, TGF-β1, Smad2, and Smad3 in the adventitia was detected by immunohistochemistry. Adventitial fibroblasts were isolated from aortic arteries of apoE knockout mice and infected with RGS3 overexpression lentivirus or empty lentivirus. The expression of RGS3, α-SMA, TGF-β1, Smad2, and Smad3 in AFs was detected by real-time polymerase chain reaction and Western blot analysis. We found that hyperlipidic diet caused significant aortic intima thickening and atherosclerotic plaques in 15-week-old apoE knockout mice. Compared to wild-type mice, RGS3 expression was lower while α-SMA, TGF-β1, Smad2, and Smad3 expression was higher in the adventitia of apoE knockout mice. In addition, lentivirus mediated overexpression of RGS3 caused decreased expression of α-SMA, TGF-β1, Smad2, and Smad3 in AFs derived from apoE(-/-) mice. In conclusion, these results suggest that RGS3 may provide protection against pathological changes of AFs and the development of atherosclerosis by inhibiting TGF-β1/Smad signalling. RGS3 may be a potential therapeutic target for atherosclerosis.

A novel regulatory role of RGS4 in STAT5B activation, neurite outgrowth and neuronal differentiation

The Regulator of G protein Signalling 4 (RGS4) is a multitask protein that interacts with and negatively modulates opioid receptor signalling. Previously, we showed that the δ-opioid receptor (δ-OR) forms a multiprotein signalling complex consisting of Gi/Go proteins and the Signal Transducer and Activator of Transcription 5B (STAT5B) that leads to neuronal differentiation and neurite outgrowth upon δ-ΟR activation. Here, we investigated whether RGS4 could participate in signalling pathways to regulate neurotropic events. We demonstrate that RGS4 interacts directly with STAT5B independently of δ-ΟR presence both in vitro and in living cells. This interaction involves the N-terminal portion of RGS4 and the DNA-binding SH3 domain of STAT5B. Expression of RGS4 in HEK293 cells expressing δ-OR and/or erythropoietin receptor results in inhibition of [D-Ser², Leu⁵, Thr⁶]-enkephalin (DSLET)-and erythropoietin-dependent STAT5B phosphorylation and subsequent transcriptional activation. DSLET-dependent neurite outgrowth of neuroblastoma cells is also blocked by RGS4 expression, whereas primary cortical cultures of RGS4 knockout mice (RGS4^-/-) exhibit enhanced neuronal sprouting after δ-OR activation. Additional studies in adult brain extracts from RGS4^-/- mice revealed increased levels of p-STAT5B. Finally, neuronal progenitor cultures from RGS4^-/- mice exhibit enhanced proliferation with concomitant increases in the mRNA levels of the anti-apoptotic STAT5B target genes bcl2 and bcl-xl. These observations suggest that RGS4 is implicated in opioid dependent neuronal differentiation and neurite outgrowth via a "non-canonical" signaling pathway regulating STAT5B-directed responses.

Regulator of G protein signaling 3 protects against cardiac hypertrophy in mice

Regulator of G protein signaling 3 (RGS3) is a negative regulator of G protein-mediated signaling. RGS3 has previously been shown to be expressed among various cell types within the mature heart. Basic and clinical studies have reported abnormal expressions of RGS3 in hypertrophic hearts and in the failing myocardium. However, the role of RGS3 in cardiac remodeling remains unclear. In this study, we investigated the effect of cardiac overexpression of human RGS3 on cardiac hypertrophy induced by aortic banding (AB) in RGS3 transgenic mice and wild-type littermates. The extent of cardiac hypertrophy was evaluated by echocardiography as well as pathological and molecular analyses of heart samples. RGS3 overexpression in the heart markedly reduced the extent of cardiac hypertrophy, fibrosis, and left ventricular dysfunction in response to AB. These beneficial effects were associated with the inhibition of MEK-ERK1/2 signaling. In vitro studies performed in cultured neonatal rat cardiomyocytes confirmed that RGS3 overexpression inhibits hypertrophic growth induced by angiotensin II, which was associated with the attenuation of MEK-ERK1/2 signaling. Therefore, cardiac overexpression of RGS3 inhibits maladaptive hypertrophy and fibrosis and improves cardiac function by blocking MEK-ERK1/2 signaling.

RGS3 controls T lymphocyte migration in a model of Th2-mediated airway inflammation

T cell migration toward sites of antigen exposure is mediated by G protein signaling and is a key function in the development of immune responses. Regulators of G protein signaling (RGS) proteins modulate G protein signaling; however, their role in the regulation of adaptive immune responses has not been thoroughly explored. Herein we demonstrated abundant expression of the Gi/Gq-specific RGS3 in activated T cells, and that diminished RGS3 expression in a T cell thymoma increased cytokine-induced migration. To examine the role of endogenous RGS3 in vivo, mice deficient in the RGS domain (RGS3(ΔRGS)) were generated and tested in an experimental model of asthma. Compared with littermate controls, the inflammation in the RGS3(ΔRGS) mice was characterized by increased T cell numbers and the striking development of perivascular lymphoid structures. Surprisingly, while innate inflammatory cells were also increased in the lungs of RGS3(ΔRGS) mice, eosinophil numbers and Th2 cytokine production were equivalent to control mice. In contrast, T cell numbers in the draining lymph nodes (dLN) were reduced in the RGS3(ΔRGS), demonstrating a redistribution of T cells from the dLN to the lungs via increased RGS3(ΔRGS) T cell migration. Together these novel findings show a nonredundant role for endogenous RGS3 in controlling T cell migration in vitro and in an in vivo model of inflammation.

Notch4-dependent antagonism of canonical TGF-β1 signaling defines unique temporal fluctuations of SMAD3 activity in sheared proximal tubular epithelial cells

Transforming growth factor-β1 (TGF-β1) is thought to drive fibrogenesis in numerous organ systems. However, we recently established that ectopic expression of TGF-β1 abrogates collagen accumulation via canonical SMAD signaling mechanisms in a shear-induced model of kidney fibrosis. We herein delineate the temporal control of endogenous TGF-β1 signaling that generates sustained synchronous fluctuations in TGF-β1 cascade activation in shear-stimulated proximal tubule epithelial cells (PTECs). During 8-h exposure to physiological shear stress (0.3 dyn/cm²), PTECs experience in situ oscillatory concentrations of active endogenous TGF-β1 that are ~10-fold greater than those detected under higher stress regimes (2-4 dyn/cm²). The elevated levels of intrinsic TGF-β1 maturation observed under physiological conditions are accompanied by persistent downstream SMAD3 activation. Pathological shear stresses (2 dyn/cm²) first elicit temporal variations in phosphorylated SMAD3 with an apparent period of ~6 h, whereas even higher stresses (4 dyn/cm²) abolish SMAD3 activation. These divergent patterns of SMAD3 activation are attributed to varying levels of Notch4-dependent phospho-SMAD3 degradation. Depletion of Notch4 in shear-stimulated PTECs eventually increases the levels of active TGF-β1 protein by approximately fivefold, recovers stable SMAD phosphorylation and ubiquitinated SMAD species, and attenuates collagen accumulation. Collectively, these data establish Notch4 as a critical mediator of shear-induced fibrosis and further reinforce the renoprotective effects of canonical TGF-β1 signaling.

Regulators of G-protein signaling in the heart and their potential as therapeutic targets

Signal transduction through G-protein-coupled receptors (GPCRs) is central for the regulation of virtually all cellular functions and has been widely implicated in human disease. Regulators of G-protein signaling (RGS proteins) belong to a diverse protein family that was originally discovered for their ability to accelerate signal termination in response to GPCR stimulation, thereby reducing the amplitude and duration of GPCR effects. All RGS proteins share a common RGS domain that interacts with G protein α subunits and mediates their biological regulation of GPCR signaling. However, RGS proteins differ widely in size and the organization of their sequences flanking the RGS domain, which contain several additional functional domains that facilitate protein-protein (or protein-lipid) interactions. RGS proteins are subject to posttranslational modifications, and, in addition, their expression, activity, and subcellular localization can be dynamically regulated. Thus, there exists a wide array of mechanisms that facilitate their proper function as modulators and integrators of G-protein signaling. Several RGS proteins have been implicated in the cardiac remodeling response and heart rate regulation, and changes in RGS protein expression and/or function are believed to participate in the pathophysiology of cardiac hypertrophy, failure and arrhythmias as well as hypertension. This review is based on recent advances in our understanding of the expression pattern, regulation, and functional role of canonical RGS proteins, with a special focus on the healthy heart and the diseased heart. In addition, we discuss their potential and promise as therapeutic targets as well as strategies to modulate their expression and function.

Priming with very low-affinity peptide ligands gives rise to CD8(+) T-cell effectors with enhanced function but with greater susceptibility to transforming growth factor (TGF)β-mediated suppression

While the effects of TCR affinity and TGFβ on CD8(+) T-cell function have been studied individually, the manner in which TCR affinity dictates susceptibility to TGFβ-mediated suppression remains unknown. To address this issue, we utilized OVA altered peptide ligands (APLs) of different affinities in the OT-I model. We demonstrate that while decreased TCR ligand affinity initially results in weakened responses, such interactions prime the resultant effector cells to respond more strongly to cognate antigen upon secondary exposure. Despite this, responses by CD8(+) T cells primed with lower-affinity TCR ligands are more effectively regulated by TGFβ. Susceptibility to TGFβ-mediated suppression is associated with downregulation of RGS3, a recently recognized negative regulator of TGFβ signaling, but not expression of TGFβ receptors I/II. These results suggest a novel tolerance mechanism whereby CD8(+) T cells are discriminately regulated by TGFβ according to the affinity of the ligand on which they were initially primed. In addition, because of the major role played by TGFβ in tumor-induced immune suppression, these results identify the affinity of the priming ligand as a primary concern in CD8(+) T-cell-mediated cancer immunotherapeutic strategies.

Thinking outside of the "RGS box": new approaches to therapeutic targeting of regulators of G protein signaling

Regulators of G protein signaling (RGS) proteins are emerging as potentially important drug targets. The mammalian RGS protein family has more than 20 members and they share a common ∼120-residue RGS homology domain or "RGS box." RGS proteins regulate signaling via G protein-coupled receptors by accelerating GTPase activity at active α subunits of G proteins of the G(q) and G(i/o) families. Most studies searching for modulators of RGS protein function have been focused on inhibiting the GTPase accelerating protein activity. However, many RGS proteins contain additional domains that serve other functions, such as interactions with proteins or subcellular targeting. Here, we discuss a rationale for therapeutic targeting of RGS proteins by regulation of expression or allosteric modulation to permit either increases or decreases in RGS function. Several RGS proteins have reduced expression or function in pathophysiological states, so strategies to increase RGS function would be useful. Because several RGS proteins are rapidly degraded by the N-end rule pathway, finding ways to stabilize them may prove to be an effective way to enhance RGS protein function.

Non-canonical functions of RGS proteins

Regulators of G protein signalling (RGS) proteins are united into a family by the presence of the RGS domain which serves as a GTPase-activating protein (GAP) for various Galpha subunits of heterotrimeric G proteins. Through this mechanism, RGS proteins regulate signalling of numerous G protein-coupled receptors. In addition to the RGS domains, RGS proteins contain diverse regions of various lengths that regulate intracellular localization, GAP activity or receptor selectivity of RGS proteins, often through interaction with other partners. However, it is becoming increasingly appreciated that through these non-RGS regions, RGS proteins can serve non-canonical functions distinct from inactivation of Galpha subunits. This review summarizes the data implicating RGS proteins in the (i) regulation of G protein signalling by non-canonical mechanisms, (ii) regulation of non-G protein signalling, (iii) signal transduction from receptors not coupled to G proteins, (iv) activation of mitogen-activated protein kinases, and (v) non-canonical functions in the nucleus.

Critical role of serum response factor in pulmonary myofibroblast differentiation induced by TGF-beta

Transforming growth factor-beta (TGF-beta) is a cytokine implicated in wound healing and in the pathogenesis of pulmonary fibrosis. TGF-beta stimulates myofibroblast differentiation characterized by expression of contractile smooth muscle (SM)-specific proteins such as SM-alpha-actin. In the present study, we examined the role of serum response factor (SRF) in the mechanism of TGF-beta-induced pulmonary myofibroblast differentiation of human lung fibroblasts (HLF). TGF-beta stimulated SM-alpha-actin expression in HLF, which paralleled with a profound induction of SRF expression and activity. Inhibition of SRF by the pharmacologic SRF inhibitor (CCG-1423), or via adenovirus-mediated transduction of SRF short hairpin RNA (shSRF), blocked the expression of both SRF and SM-alpha-actin in response to TGF-beta without affecting Smad-mediated signaling of TGF-beta. However, forced expression of SRF on its own did not promote SM-alpha-actin expression, whereas expression of the constitutively transactivated SRF fusion protein (SRF-VP16) was sufficient to induce SM-alpha-actin expression, suggesting that both expression and transactivation of SRF are important. Activation of protein kinase A (PKA) by forskolin or iloprost resulted in a significant inhibition of SM-alpha-actin expression induced by TGF-beta, and this was associated with inhibition of both SRF expression and activity, but not of Smad-mediated gene transcription. In summary, this is the first direct demonstration that TGF-beta-induced pulmonary myofibroblast differentiation is mediated by SRF, and that inhibition of myofibroblast differentiation by PKA occurs through down-regulation of SRF expression levels and SRF activity, independent of Smad signaling.