Gαi2 Protein Inhibition Blocks Chemotherapy- and Anti-Androgen-Induced Prostate Cancer Cell Migration

We have previously shown that heterotrimeric G-protein subunit alphai2 (Gαi2) is essential for cell migration and invasion in prostate, ovarian and breast cancer cells, and novel small molecule inhibitors targeting Gαi2 block its effects on migratory and invasive behavior. In this study, we have identified potent, metabolically stable, second generation Gαi2 inhibitors which inhibit cell migration in prostate cancer cells. Recent studies have shown that chemotherapy can induce the cancer cells to migrate to distant sites to form metastases. In the present study, we determined the effects of taxanes (docetaxel), anti-androgens (enzalutamide and bicalutamide) and histone deacetylase (HDAC) inhibitors (SAHA and SBI-I-19) on cell migration in prostate cancer cells. All treatments induced cell migration, and simultaneous treatments with new Gαi2 inhibitors blocked their effects on cell migration. We concluded that a combination treatment of Gαi2 inhibitors and chemotherapy could blunt the capability of cancer cells to migrate and form metastases.

Sensing and avoiding sick conspecifics requires Gαi2+ vomeronasal neurons

BACKGROUND

Rodents utilize chemical cues to recognize and avoid other conspecifics infected with pathogens. Infection with pathogens and acute inflammation alter the repertoire and signature of olfactory stimuli emitted by a sick individual. These cues are recognized by healthy conspecifics via the vomeronasal or accessory olfactory system, triggering an innate form of avoidance behavior. However, the molecular identity of the sensory neurons and the higher neural circuits involved in the detection of sick conspecifics remain poorly understood.

RESULTS

We employed mice that are in an acute state of inflammation induced by systemic administration of lipopolysaccharide (LPS). Through conditional knockout of the G-protein Gαi2 and deletion of other key sensory transduction molecules (Trpc2 and a cluster of 16 vomeronasal type 1 receptors), in combination with behavioral testing, subcellular Ca²⁺ imaging, and pS6 and c-Fos neuronal activity mapping in freely behaving mice, we show that the Gαi2⁺ vomeronasal subsystem is required for the detection and avoidance of LPS-treated mice. The active components underlying this avoidance are contained in urine whereas feces extract and two selected bile acids, although detected in a Gαi2-dependent manner, failed to evoke avoidance behavior. Our analyses of dendritic Ca²⁺ responses in vomeronasal sensory neurons provide insight into the discrimination capabilities of these neurons for urine fractions from LPS-treated mice, and how this discrimination depends on Gαi2. We observed Gαi2-dependent stimulation of multiple brain areas including medial amygdala, ventromedial hypothalamus, and periaqueductal grey. We also identified the lateral habenula, a brain region implicated in negative reward prediction in aversive learning, as a previously unknown target involved in these tasks.

CONCLUSIONS

Our physiological and behavioral analyses indicate that the sensing and avoidance of LPS-treated sick conspecifics depend on the Gαi2 vomeronasal subsystem. Our observations point to a central role of brain circuits downstream of the olfactory periphery and in the lateral habenula in the detection and avoidance of sick conspecifics, providing new insights into the neural substrates and circuit logic of the sensing of inflammation in mice.

Gαi2 regulates the adult myogenesis of masticatory muscle satellite cells

Although similar to trunk and limb skeletal muscles, masticatory muscles are believed as unique in both developmental origins and myogenesis. Gαi2 has been demonstrated to promote muscle hypertrophy and muscle satellite cell differentiation in limb muscles. However, the effect of Gαi2 on masticatory muscles is still unexplored. This study aimed to identify the role of Gαi2 in the proliferation and differentiation of masticatory muscle satellite cells, further exploring the metabolic mechanism of masticatory muscles. The proliferation rate, myotube size, fusion index of masticatory muscle satellite cells and Pax7, Myf5, MyoD, Tcf21 and Musculin expressions were significantly decreased by Gαi2 knockdown, while in cells infected with AdV4-Gαi2, the proliferation rate, myotube size, fusion index and Tbx1 expression were significantly increased. Masticatory muscle satellite cells also displayed phenotype transformation as Gαi2 changed. In addition, Gαi2 altered myosin heavy chain (MyHC) isoforms of myotubes with less MyHC-2A expression in siGαi2 group and more MyHC-slow expression in AdV4-Gαi2 group. In conclusion, Gαi2 could positively affect the adult myogenesis of masticatory muscle satellite cells and maintain the superiority of MyHC-slow. Masticatory muscle satellite cells may have their unique Gαi2-regulated myogenic transcriptional networks, although they may share some common characteristics with trunk and limb muscles.

Sensory Detection by the Vomeronasal Organ Modulates Experience-Dependent Social Behaviors in Female Mice

In mice, social behaviors are largely controlled by the olfactory system. Pheromone detection induces naïve virgin females to retrieve isolated pups to the nest and to be sexually receptive to males, but social experience increases the performance of both types of innate behaviors. Whether animals are intrinsically sensitive to the smell of conspecifics, or the detection of olfactory cues modulates experience for the display of social responses is currently unclear. Here, we employed mice with an olfactory-specific deletion of the G protein Gαi2, which partially eliminates sensory function in the vomeronasal organ (VNO), to show that social behavior in female mice results from interactions between intrinsic mechanisms in the vomeronasal system and experience-dependent plasticity. In pup- and sexually-naïve females, Gαi2 deletion elicited a reduction in pup retrieval behavior, but not in sexual receptivity. By contrast, experienced animals showed normal maternal behavior, but the experience-dependent increase in sexual receptivity was incomplete. Further, lower receptivity was accompanied by reduced neuronal activity in the anterior accessory olfactory bulb and the rostral periventricular area of the third ventricle. Therefore, neural mechanisms utilize intrinsic sensitivity in the mouse vomeronasal system and enable plasticity to display consistent social behavior.

Small Molecule Inhibitors Targeting Gαi2 Protein Attenuate Migration of Cancer Cells

Heterotrimeric G-proteins are ubiquitously expressed in several cancers, and they transduce signals from activated G-protein coupled receptors. These proteins have numerous biological functions, and they are becoming interesting target molecules in cancer therapy. Previously, we have shown that heterotrimeric G-protein subunit alphai2 (Gαi2) has an essential role in the migration and invasion of prostate cancer cells. Using a structure-based approach, we have synthesized optimized small molecule inhibitors that are able to prevent specifically the activation of the Gαi2 subunit, keeping the protein in its inactive GDP-bound state. We observed that two of the compounds (13 and 14) at 10 μΜ significantly inhibited the migratory behavior of the PC3 and DU145 prostate cancer cell lines. Additionally, compound 14 at 10 μΜ blocked the activation of Gαi2 in oxytocin-stimulated prostate cancer PC3 cells, and inhibited the migratory capability of DU145 cells overexpressing the constitutively active form of Gαi2, under basal and EGF-stimulated conditions. We also observed that the knockdown or inhibition of Gαi2 negatively regulated migration of renal and ovarian cancer cell lines. Our results suggest that small molecule inhibitors of Gαi2 have potential as leads for discovering novel anti-metastatic agents for attenuating the capability of cancer cells to spread and invade to distant sites.

ELMO2 association with Gαi2 regulates pancreatic cancer cell chemotaxis and metastasis

Background

Pancreatic cancer is a highly lethal disease. Nearly half of the patients have distant metastasis and remain asymptomatic. Emerging evidence suggests that the chemokine, CXCL12, has a role in cancer metastasis. The interaction between CXCL12 and CXCR4 activates heterotrimeric G proteins, which regulates actin polymerization and cancer cell migration. However, the molecular mechanisms underlying pancreatic cancer cell migration are still largely obscure. Here, we addressed the role of ELMO2 in chemotaxis and metastasis of pancreatic cancer cells.

Methods

Pancreatic cancer cell lines PANC-1 and AsPC-1 and siRNA-mediated knockdown of ELMO2 were used to determine the effects of ELMO2 on cancer cell chemotaxis, invasion, migration. Co-immunoprecipitation assays were carried out to identify interacting partners of ELMO2.

Results

ELMO2 knockdown inhibited pancreatic cancer cell chemotaxis, migration, invasion, and F-actin polymerization. Co-immunoprecipitation assays revealed that ELMO2 interacted with Gαi2 and that CXCL12 triggered Gα i2-dependent membrane translocation of ELMO2. Thus, ELMO2 is a potential therapeutic target for pancreatic cancer.

Heterotrimeric G-protein subunit Gαi2 contributes to agonist-sensitive apoptosis and degranulation in murine platelets

Gαi2 , a heterotrimeric G-protein subunit, regulates various cell functions including ion channel activity, cell differentiation, proliferation and apoptosis. Platelet-expressed Gαi2 is decisive for the extent of tissue injury following ischemia/reperfusion. However, it is not known whether Gαi2 plays a role in the regulation of platelet apoptosis, which is characterized by caspase activation, cell shrinkage and cell membrane scrambling with phosphatidylserine (PS) translocation to the platelet surface. Stimulators of platelet apoptosis include thrombin and collagen-related peptide (CoRP), which are further known to enhance degranulation and activation of αIIb β3-integrin and caspases. Using FACS analysis, we examined the impact of agonist treatment on activation and apoptosis in platelets drawn from mice lacking Gαi2 and their wild-type (WT) littermates. As a result, treatment with either thrombin (0.01 U/mL) or CoRP (2 μg/mL or 5 μg/mL) significantly upregulated PS-exposure and significantly decreased forward scatter, reflecting cell size, in both genotypes. Exposure to CoRP triggered a significant increase in active caspase 3, ceramide formation, surface P-selectin, and αIIb β3-integrin activation. These molecular alterations were significantly less pronounced in Gαi2 -deficient platelets as compared to WT platelets. In conclusion, our data highlight a previously unreported role of Gαi2 signaling in governing platelet activation and apoptosis.

Decreased intracellular chloride promotes ADP induced platelet activation through inhibition of cAMP/PKA instead of activation of Lyn/PI3K/Akt pathway

Decrease of chloride concentration contributes to cardiovascular diseases, however, whether decrease of chloride concentration is involved in platelet activation remains elusive. In the present study, we found that ACI patients had lower serum chloride which would be rescued after Aspirin administration. ADP induced chloride concentration reduction in platelets. Blockade of chloride channel prevented ADP-induced platelet adhesion, activation and aggregation, however, decreasing the extracellular chloride concentration promoted ADP-induced platelet adhesion and activation. Decrease of the extracellular chloride concentration facilitated the inactivation of Src family kinase Lyn, which was not involved in PI3K/Akt phosphorylation. Nevertheless, low chloride concentration promoted the production of platelet cytosol Gαi2 subunit. This subunit prevents AC from converting ATP into cAMP, which therefore, inhibited the phosphorylation of PKA to promote platelet activation. In conclusion, decreased intracellular chloride promotes ADP induced platelet activation through the Gαi2/cAMP/PKA pathway instead of the Lyn/PI3K/Akt signal pathway.

Insulin secretion stimulated by L-arginine and its metabolite L-ornithine depends on Gα(i2)

Bordetella pertussis toxin (PTx), also known as islet-activating protein, induces insulin secretion by ADP-ribosylation of inhibitory G proteins. PTx-induced insulin secretion may result either from inactivation of Gα(o) proteins or from combined inactivation of Gα(o), Gα(i1), Gα(i2), and Gα(i3) isoforms. However, the specific role of Gα(i2) in pancreatic β-cells still remains unknown. In global (Gα(i2)(-/-)) and β-cell-specific (Gα(i2)(βcko)) gene-targeted Gα(i2) mouse models, we studied glucose homeostasis and islet functions. Insulin secretion experiments and intracellular Ca²⁺ measurements were used to characterize Gα(i2) function in vitro. Gα(i2)(-/-) and Gα(i2)(βcko) mice showed an unexpected metabolic phenotype, i.e., significantly lower plasma insulin levels upon intraperitoneal glucose challenge in Gα(i2)(-/-) and Gα(i2)(βcko) mice, whereas plasma glucose concentrations were unchanged in Gα(i2)(-/-) but significantly increased in Gα(i2)(βcko) mice. These findings indicate a novel albeit unexpected role for Gα(i2) in the expression, turnover, and/or release of insulin from islets. Detection of insulin secretion in isolated islets did not show differences in response to high (16 mM) glucose concentrations between control and β-cell-specific Gα(i2)-deficient mice. In contrast, the two- to threefold increase in insulin secretion evoked by L-arginine or L-ornithine (in the presence of 16 mM glucose) was significantly reduced in islets lacking Gα(i2). In accord with a reduced level of insulin secretion, intracellular calcium concentrations induced by the agonistic amino acid L-arginine did not reach control levels in β-cells. The presented analysis of gene-targeted mice provides novel insights in the role of β-cell Gα(i2) showing that amino acid-induced insulin-release depends on Gα(i2).

LPA Stimulates the Phosphorylation of p130Cas via Gαi2 in Ovarian Cancer Cells

Ovarian cancer is the most deadly gynecological cancer, with previous studies implicating lysophosphatidic acid (LPA) in the progression of approximately 90% of all ovarian cancers. LPA potently stimulates the tyrosine phosphorylation of p130Cas, a scaffolding protein, which, upon phosphorylation, recruits an array of signaling molecules to promote tumor cell migration. Our work presented here identifies Gαi2 as the major G protein involved in tyrosine phosphorylation of p130Cas in a panel of ovarian cancer cells consisting of HeyA8, SKOV3, and OVCA429. Our results also indicate that the G12 family of G proteins that are also involved in LPA-mediated migration inhibits tyrosine phosphorylation of p130Cas. Using p130Cas siRNA, we demonstrate that p130Cas is a necessary downstream component of LPA Gαi2-induced migration and collagen-1 invasion of ovarian cancer cells. Considering the fact that LPA stimulates invasive migration through the coordination of multiple downstream signaling pathways, our current study identifies a separate unique signaling node involving p130Cas and Gαi2 in mediating LPA-mediated invasive migration of ovarian cancer cells.

Fluoxetine Up-Regulates Bcl-xL Expression in Rat C6 Glioma Cells

OBJECTIVE

To analyze both differentially expressed genes and the Bcl-xL protein expression after acute and chronic treatment with fluoxetine in rat C6 glioma cells.

METHODS

C6 glioma cells were cultured for 24 h or 72 h after treatment with 10 µM fluoxetine, and gene expression patterns were observed using microarray and qRT-PCR. Then, cells were cultured for 6 h, 24 h, 72 h or 96 h after treatment with 10 µM fluoxetine, and the expression of Bcl-xL protein was measured using western blot.

RESULTS

As determined by microarray, treatment with fluoxetine for 24 h up-regulated 33 genes (including Bcl-xL and NCAM140) and down-regulated 7 genes (including cyclin G-associated kinase). Treatment with fluoxetine for 72 h up-regulated 53 genes (including Gsα and Bcl-xL) and down-regulated 77 genes (including Gαi2 and annexin V). Based on the qRT-PCR results, there was an increase in Gsα mRNA and a decrease in Gαi2 mRNA at 72 h in fluoxetine-treated cells as compared to control, a result that was consistent with microarray. We also observed an increase in Bcl-xL mRNA (both at 24 h and at 72 h) in fluoxetine-treated cells as compared to control, demonstrating a tendency to increase gradually. Bcl-xL protein expression increased as the duration of fluoxetine treatment increased.

CONCLUSION

These results suggest that chronic treatment with fluoxetine not only initiates the cAMP pathway through inducing Gsα expression but also induces Bcl-xL expression, thus inhibiting apoptosis.