Heterotrimeric G protein signaling without GPCRs: The Gα-binding-and-activating (GBA) motif

Heterotrimeric G proteins (Gαβγ) are molecular switches that relay signals from 7-transmembrane receptors located at the cell surface to the cytoplasm. The function of these receptors is so intimately linked to heterotrimeric G proteins that they are named G protein-coupled receptors (GPCRs), showcasing the interdependent nature of this archetypical receptor-transducer axis of transmembrane signaling in eukaryotes. It is generally assumed that activation of heterotrimeric G protein signaling occurs exclusively by the action of GPCRs, but this idea has been challenged by the discovery of alternative mechanisms by which G proteins can propagate signals in the cell. This review will focus on a general principle of G protein signaling that operates without the direct involvement of GPCRs. The mechanism of G protein signaling reviewed here is mediated by a class of G protein regulators defined by containing an evolutionarily conserved sequence named the Gα-binding-and-activating (GBA) motif. Using the best characterized proteins with a GBA motif as examples, Gα-interacting vesicle-associated protein (GIV)/Girdin and dishevelled-associating protein with a high frequency of leucine residues (DAPLE), this review will cover (i) the mechanisms by which extracellular cues not relayed by GPCRs promote the coupling of GBA motif-containing regulators with G proteins, (ii) the structural and molecular basis for how GBA motifs interact with Gα subunits to facilitate signaling, (iii) the relevance of this mechanism in different cellular and pathological processes, including cancer and birth defects, and (iv) strategies to manipulate GBA-G protein coupling for experimental therapeutics purposes, including the development of rationally engineered proteins and chemical probes.

Growth signaling autonomy in circulating tumor cells aids metastatic seeding

Self-sufficiency (autonomy) in growth signaling, the earliest recognized hallmark of cancer, is fueled by the tumor cell's ability to "secrete-and-sense" growth factors (GFs); this translates into cell survival and proliferation that is self-sustained by autocrine/paracrine secretion. A Golgi-localized circuitry comprised of two GTPase switches has recently been implicated in the orchestration of growth signaling autonomy. Using breast cancer cells that are either endowed or impaired (by gene editing) in their ability to assemble the circuitry for growth signaling autonomy, here we define the transcriptome, proteome, and phenome of such an autonomous state, and unravel its role during cancer progression. We show that autonomy is associated with enhanced molecular programs for stemness, proliferation, and epithelial-mesenchymal plasticity. Autonomy is both necessary and sufficient for anchorage-independent GF-restricted proliferation and resistance to anticancer drugs and is required for metastatic progression. Transcriptomic and proteomic studies show that autonomy is associated, with a surprising degree of specificity, with self-sustained epidermal growth factor receptor (EGFR)/ErbB signaling. Derivation of a gene expression signature for autonomy revealed that growth signaling autonomy is uniquely induced in circulating tumor cells (CTCs), the harshest phase in the life of tumor cells when it is deprived of biologically available epidermal growth factor (EGF). We also show that autonomy in CTCs tracks therapeutic response and prognosticates outcome. These data support a role for growth signaling autonomy in multiple processes essential for the blood-borne dissemination of human breast cancer.

Upregulation of girdin delays endothelial cell apoptosis via promoting engulfment of platelets

BACKGROUND

Endothelial cells are crucial in maintaining the homeostasis of the blood-brain barrier. Girders of actin filament (Girdin) and phosphor (p)-Girdin are essential for the engulfment of human brain microvascular endothelial cells (HBMECs) into platelets (PLTs), but the potential mechanism remains unclear and requires further study.

METHODS

Following PLT and cytochalasin D treatment, Hoechst 33,342 detected apoptosis. The transfection efficiency of the short hairpin RNA targeting Girdin (sh-Girdin) or overexpressing Girdin (OE-Girdin) was determined using western blotting. Sh-Girdin, OE-Girdin, mutated Girdin (m-Girdin), and microfilament binding region deleted Girdin (Del-Girdin) were transfected into HBMECs under PLT conditions. Subsequently, the engulfment of HBMECs by PLTs was detected by flow cytometry and transmission electron microscopy. Girdin and phosphorylated (p)-Girdin levels were quantified by western blot. The positive expression of Girdin was measured by immunohistochemistry (IHC). The localization of PLT, Girdin, and p-Girdin and the engulfment of HBMECs in PLTs were analyzed by confocal microscopy.

RESULT

Cytochalasin D overturned the inhibitory effect of PLT on cell apoptosis. OE-Girdin enhanced the fluorescent intensity of PLT-labelling and the engulfment of HBMECs by PLTs, while sh-Girdin, m-Girdin, and Del-Girdin ran reversely. OE-Girdin elevated the Girdin and p-Girdin levels, while sh-Girdin and Del-Girdin were the opposite, but m-Girdin did not affect the p-Girdin and Girdin levels.

CONCLUSION

Girdin and p-Girdin were co-located with PLTs in HBMECs. The over-expression of Girdin was identified as being associated with the increasing engulfment of PTLs. Girdin may be an effective target to alleviate endothelial cell apoptosis.

An unusual signal transducer GIV/Girdin engages in the roles of adipocyte-derived hormone leptin in liver fibrosis

Obese patients usually have hyperleptinemia and are prone to develop liver fibrosis. Leptin is intimately linked to liver fibrogenesis, a multi-receptor-driven disease. Gα-Interacting Vesicle-associated protein (GIV) functions as a multimodular signal transducer and a guanine nucleotide exchange factor for Gi controling key signalings downstream of diverse receptors. This study aimed to examine the roles of GIV in leptin-caused liver fibrosis and employed the culture-activated hepatic stellate cells (HSCs) and leptin-deficient mice, respectively. Results indicated that leptin upregulated GIV expression in HSCs. GIV was involved in leptin-induced HSC activation and liver fibrosis. GIV mediated leptin regulation of TIMP1, MMP9, PDGFβ receptor and TGFβ receptor and was required for leptin stimulating the pathways of Erk1/2, Akt1, and Smad3. GIV was also a mediator for leptin-regulation of Cyclin D1 and Caspase-3 activity but GIV reduced Caspase-3 level independently of leptin in vivo. Erk1/2 signaling, Egr1 and c-Jun were associated with the effect of leptin on GIV expression in HSCs. Leptin-induced Erk1/2 signaling increased Egr1 and p-c-Jun levels and promoted their binding to GIV promoter at the sites between -190 bp and -180 bp and between -382 bp and - 376 bp, respectively. Egr1 knockdown lessened leptin-upregulation of GIV in vitro and in vivo. In human cirrhotic livers, the increase in GIV protein level parallelled with the elevated p-Erk1/2 and Egr1 levels in HSCs. In summary, the unusual signal transducer GIV was identified as an important mediator in leptin-induced liver fibrosis. GIV may have significant implications in liver fibrosis progression of obese patients with hyperleptinaemia.

Girdin Promotes Tumorigenesis and Chemoresistance in Lung Adenocarcinoma by Interacting with PKM2

Girdin, an Akt substrate, has been reported to promote tumorigenesis in various tumors. However, the role of Girdin in a spontaneous tumor model has not yet been explored. Here, we studied the role of Girdin in lung adenocarcinoma (LUAD) using the autochthonous mouse model and found that Girdin led to LUAD progression and chemoresistance by enhancing the Warburg effect. Mechanistically, Girdin interacted with pyruvate kinase M2 (PKM2), which played a vital role in aerobic glycolysis. Furthermore, Girdin impaired Platelet Derived Growth Factor Receptor Beta (PDGFRβ) degradation, which in turn, promoted PKM2 tyrosine residue 105 (Y105) phosphorylation and inhibited PKM2 activity, subsequently promoting aerobic glycolysis in cancer cells. Taken together, our study demonstrates that Girdin is a crucial regulator of tumor growth and may be a potential therapeutic target for overcoming the resistance of LUAD cells to chemotherapy.

Knockdown of Girdin Induced Apoptosis of Glioblastoma Cells via the Mitochondrion Signaling Pathway

Glioblastoma is the most common primary brain tumor with poor survival rate and without effective treatment strategy. However, the influence of Girdin on human glioblastoma and the underlying molecular mechanisms have yet to be uncovered. We mainly investigated the role of Girdin in glioblastoma cells apoptosis. First, we examined Girdin expression in 90 glioma patients by using immunohistochemistry (IHC) and analyzed its association with patients' prognosis. The results showed that the expression of Girdin was positively associated with the histological grade of glioma, and glioma patients with high Girdin expression had a poor prognosis. Next, proliferation assay, Colony formation assay and Cell Counting Kit-8 (CCK-8) results showed that knockdown of Girdin suppressed proliferation and reduced cell survival rate. Flow cytometry and DAPI staining results showed that knockdown of Girdin induced apoptosis in LN229 cells. Western blot results suggested that reduction of Gridin increased the level of Cytochrome C (Cyt-C) and Bad while decreased the expression of Bcl-2 and p-AKT. Moreover, subcutaneous mouse xenograft model was used to validate the role of Girdin in glioblastoma apoptosis. Consistently, in vivo assays showed that knockdown of Girdin inhibited the growth of the grafted tumor and increased the level of Cyt-C and Bad. These findings demonstrated that knockdown of Girdin may induce Bad expression and reduce Bcl-2 expression by inhibiting the activation of AKT, leading to the release of Cyt-C from mitochondria, thereby promoting glioblastoma cells apoptosis.

The mechanism of Girdin in degenerative brain disease caused by high glucose stimulation

Girdin, as an actin-binding protein, plays a major role in maintaining the stability of the actin skeleton structure and affects the growth, development, and migration of neurons. This study discusses the mechanism of Girdin in brain degeneration caused by high glucose stimulation. We examined the expression of Girdin in diabetic patients. The positive expression rate of Girdin in the diabetic group was 17.2% (5/29), which was obviously lower than the positive expression rate of 83.3% (20/24) in the non-diabetic group. We examined the expression of Girdin and its signaling pathway-related proteins Akt and STAT3 in hippocampal neurons induced by high glucose. The results showed that, in contrast to the control group (glucose concentration = 25 mmol/L), the expression of Girdin in the high-glucose group (glucose concentration = 225 mmol/L) was reduced (P < 0.05); the phosphorylation levels of Akt and STAT3 related to Girdin signaling pathway were also reduced (P < 0.05). Under high-glucose stimulation, the structure of neurons is abnormal, such as the reduction or disappearance of dendritic spines, and the number of neurons is reduced. In addition, Girdin and Akt were less expressed in neurons and synapses, especially the most obvious reduction in synaptic terminals. The activity of Girdin and its signaling pathway-related proteins Akt and STAT3 decreased in neurons under high glucose stimulation, indicating that the mechanism of Girdin in brain degeneration caused by high glucose stimulation was closely related to the Akt and STAT3 pathways.

GRAPHIC ABSTRACT

The mechanism of Girdin in degenerative brain disease caused by high glucose stimulation. This article discusses the mechanism of Girdin in brain degeneration induced by high glucose stimulation. The expression of Girdin in the diabetic group was significantly lower than that in the non-diabetic group. The expression of Girdin and its signaling pathway-related proteins Akt and STAT3 in hippocampal neurons was significantly reduced under high glucose stimulation. Under high glucose stimulation, the structure of neurons is abnormal and the number decreases; synapses become shorter. It indicates that the mechanism of brain degeneration caused by high glucose stimulation by Girdin is closely related to the Akt and STAT3 pathways.

GIV/Girdin, a non-receptor modulator for Gαi/s, regulates spatiotemporal signaling during sperm capacitation and is required for male fertility

For a sperm to successfully fertilize an egg, it must first undergo capacitation in the female reproductive tract and later undergo acrosomal reaction (AR) upon encountering an egg surrounded by its vestment. How premature AR is avoided despite rapid surges in signaling cascades during capacitation remains unknown. Using a combination of conditional knockout (cKO) mice and cell-penetrating peptides, we show that GIV (CCDC88A), a guanine nucleotide-exchange modulator (GEM) for trimeric GTPases, is highly expressed in spermatocytes and is required for male fertility. GIV is rapidly phosphoregulated on key tyrosine and serine residues in human and murine spermatozoa. These phosphomodifications enable GIV-GEM to orchestrate two distinct compartmentalized signaling programs in the sperm tail and head; in the tail, GIV enhances PI3K→Akt signals, sperm motility and survival, whereas in the head it inhibits cAMP surge and premature AR. Furthermore, GIV transcripts are downregulated in the testis and semen of infertile men. These findings exemplify the spatiotemporally segregated signaling programs that support sperm capacitation and shed light on a hitherto unforeseen cause of infertility in men.

Roles of metformin-mediated girdin expression in metastasis of epithelial ovarian cancer

Antimetastatic effect of Metformin has been documented in epithelial ovarian cancer (EOC). Presently, we investigated the regulatory mechanism of Metformin in EOC metastasis. First, Girdin was significantly enhanced in EOC tumorous tissues and cell lines. Seconded, knockdown of Girdin significantly suppressed EOC cell viability, migration, and invasion, while upregulation of Girdin produced the opposite effects in vitro and facilitated lung metastasis in EOC cell xenograft in vivo. In addition, we confirmed that the inhibitory effect of Metformin on Girdin expression. Mechanistically, the oncogenic effects of Girdin could be reversed by LY294002 (an AKT pathway inhibitor) and Metformin. These results suggested that Metformin attenuated EOC metastasis through Girdin and targeting Girdin may be a promising therapeutic strategy for EOC in the future.

Complementary biosensors reveal different G-protein signaling modes triggered by GPCRs and non-receptor activators

It has become evident that activation of heterotrimeric G-proteins by cytoplasmic proteins that are not G-protein-coupled receptors (GPCRs) plays a role in physiology and disease. Despite sharing the same biochemical guanine nucleotide exchange factor (GEF) activity as GPCRs in vitro, the mechanisms by which these cytoplasmic proteins trigger G-protein-dependent signaling in cells have not been elucidated. Heterotrimeric G-proteins can give rise to two active signaling species, Gα-GTP and dissociated Gβγ, with different downstream effectors, but how non-receptor GEFs affect the levels of these two species in cells is not known. Here, a systematic comparison of GPCRs and three unrelated non-receptor proteins with GEF activity in vitro (GIV/Girdin, AGS1/Dexras1, and Ric-8A) revealed high divergence in their contribution to generating Gα-GTP and free Gβγ in cells directly measured with live-cell biosensors. These findings demonstrate fundamental differences in how receptor and non-receptor G-protein activators promote signaling in cells despite sharing similar biochemical activities in vitro.

The relationship among Girdin DNA methylation, its high expression, and immune infiltration in hepatocellular carcinoma: Clues from in silico analysis

Objective: The aim of the present study was to explore the relationship among Girdin DNA methylation, its high expression, and immune infiltration in human hepatocellular carcinoma (HCC).

Materials and methods: The Cancer Genome Atlas (TCGA), Gene Expression Omnibus (GEO), and International Cancer Genome Consortium (ICGC) databases were used to compare Girdin mRNA expression between HCC tissues and normal tissues, and determine the relationship between Girdin expression and HCC prognosis. TCGA database was also used to analyze the expression of Girdin and its methylation status, as well as the relationship between Girdin DNA methylation and HCC prognosis. The Tumor IMmune Estimation Resource (TIMER) database was used to explore the correlation between Girdin expression and HCC immune infiltration.

Results: Girdin expression was elevated in HCC tissues compared with that in normal tissues. The degree of methylation at cg03188526, a CpG site in the Girdin gene body, was positively correlated with Girdin mRNA expression, while high Girdin expression and cg03188526 hypermethylation were both correlated with poor HCC prognosis. Additionally, HCC tissue with high Girdin expression exhibited abundant immune infiltration, and the high Girdin expression was associated with a worse prognosis in macrophage-enriched HCC specimens.

Conclusion: Our findings indicated that Girdin likely functions as an oncogene in HCC and that hypermethylation at cg03188526 in the Girdin gene body may explain the high Girdin expression levels in HCC tissue. Furthermore, we report for the first time that the adverse effects of high Girdin expression in HCC patients may be partially mediated by tumor macrophage infiltration.

TLR4 signaling and macrophage inflammatory responses are dampened by GIV/Girdin

Sensing of pathogens by Toll-like receptor 4 (TLR4) induces an inflammatory response; controlled responses confer immunity but uncontrolled responses cause harm. Here we define how a multimodular scaffold, GIV (a.k.a. Girdin), titrates such inflammatory response in macrophages. Upon challenge with either live microbes or microbe-derived lipopolysaccharides (a ligand for TLR4), macrophages with GIV mount a more tolerant (hypo-reactive) transcriptional response and suppress proinflammatory cytokines and signaling pathways (i.e., NFkB and CREB) downstream of TLR4 compared to their GIV-depleted counterparts. Myeloid-specific gene-depletion studies confirmed that the presence of GIV ameliorates dextran sodium sulfate-induced colitis and sepsis-induced death. The antiinflammatory actions of GIV are mediated via its C-terminally located TIR-like BB-loop (TILL) motif which binds the cytoplasmic TIR modules of TLR4 in a manner that precludes receptor dimerization; such dimerization is a prerequisite for proinflammatory signaling. Binding of GIV's TILL motif to TIR modules inhibits proinflammatory signaling via other TLRs, suggesting a convergent paradigm for fine-tuning macrophage inflammatory responses.

Complex roles of the actin-binding protein Girdin/GIV in DNA damage-induced apoptosis of cancer cells

The actin‐binding protein Girdin is a hub protein that interacts with multiple proteins to regulate motility and Akt and trimeric G protein signaling in cancer cells. Girdin expression correlates with poor outcomes in multiple human cancers. However, those findings are not universal, as they depend on study conditions. Those data suggest that multiple aspects of Girdin function and its role in tumor cell responses to anticancer therapeutics must be reconsidered. In the present study, we found that Girdin is involved in DNA damage‐induced cancer cell apoptosis. An esophageal cancer cell line that exhibited high Girdin expression showed a marked sensitivity to UV‐mediated DNA damage compared to a line with low Girdin expression. When transcriptional activation of endogenous Girdin was mediated by an engineered CRISPR/Cas9 activation system, sensitivity to DNA damage increased in both stationary and migrating HeLa cancer cells. High Girdin expression was associated with dysregulated cell cycle progression and prolonged G₁ and M phases. These features were accompanied by p53 activation, which conceivably increases cancer cell vulnerability to UV exposure. These data highlight the importance of understanding complex Girdin functions that influence cancer cell sensitivity to therapeutics.

Optogenetic activation of heterotrimeric G-proteins by LOV2GIVe, a rationally engineered modular protein

Heterotrimeric G-proteins are signal transducers involved in mediating the action of many natural extracellular stimuli and many therapeutic agents. Non-invasive approaches to manipulate the activity of G-proteins with high precision are crucial to understand their regulation in space and time. Here, we developed LOV2GIVe, an engineered modular protein that allows the activation of heterotrimeric G-proteins with blue light. This optogenetic construct relies on a versatile design that differs from tools previously developed for similar purposes, that is metazoan opsins, which are light-activated G-protein-coupled receptors (GPCRs). Instead, LOV2GIVe consists of the fusion of a G-protein activating peptide derived from a non-GPCR regulator of G-proteins to a small plant protein domain, such that light uncages the G-protein activating module. Targeting LOV2GIVe to cell membranes allowed for light-dependent activation of Gi proteins in different experimental systems. In summary, LOV2GIVe expands the armamentarium and versatility of tools available to manipulate heterotrimeric G-protein activity.

The DISC1-Girdin complex - a missing link in signaling to the T cell cytoskeleton

In this study, using Jurkat cells, we show that DISC1 (disrupted in schizophrenia 1) and Girdin (girders of actin filament) are essential for typical actin accumulation at the immunological synapse. Furthermore, DISC1, Girdin and dynein are bound in a complex. Although this complex initially forms as a central patch at the synapse, it relocates to a peripheral ring corresponding to the peripheral supramolecular activation cluster (pSMAC). In the absence of DISC1, the classic actin ring does not form, cell spreading is blocked, and the dynein complex fails to relocate to the pSMAC. A similar effect is seen when Girdin is deleted. When cells are treated with inhibitors of actin polymerization, the dynein-NDE1 complex is lost from the synapse and the microtubule-organizing center fails to translocate, suggesting that actin and dynein might be linked. Upon stimulation of T cell receptors, DISC1 becomes associated with talin, which likely explains why the dynein complex colocalizes with the pSMAC. These results show that the DISC1-Girdin complex regulates actin accumulation, cell spreading and distribution of the dynein complex at the synapse.This article has an associated First Person interview with the first author of the paper.

Quantitative acetylome and phosphorylome analysis reveals Girdin affects pancreatic cancer progression through regulating Cortactin

The actin-binding protein Girdin is involved in a variety of cellular processes, including pancreatic cancer. The objective of this study is to explore the role and the mechanism of Girdin in pancreatic cancer by quantitative acetylome and phosphorylome analysis. We firstly found that Girdin was overexpressed in pancreatic cancer tissue and increased expression of Girdin was associated with tumor size and stage of patients with pancreatic cancer. We established the shRNA knockdown of Girdin in PANC-1 and Aspc-1 cells, and we found that shGirdin inhibited proliferation, migration and invasion, and promoted apoptosis. Subsequently, we identified and quantified 5,338 phosphorylated sites in 2,263 proteins that changed in response to Girdin knockdown, and identified a similar set of Girdin-responsive acetylome data as well. Additional data revealed that down-regulation of Girdin affected Cortactin phosphorylation and acetylation, suggesting Cortactin as an important regulatory target of Girdin. Moreover, we found that overexpression of Cortactin could rescue the effect of shGirdin on proliferation, apoptosism, migration and invasion of pancreatic cancer cells. In general, our results provided new insights into the mechanisms of Girdin function including cell proliferation, migration and invasion, and offer biomarker candidates for clinical evaluation of Girdin.

MiR-328-3p inhibits cell proliferation and metastasis in colorectal cancer by targeting Girdin and inhibiting the PI3K/Akt signaling pathway

MiR-328-3p has been reported to be downregulated and serve as a tumor suppressor in several cancers. Previous studies only have reported the downregulation of miR-328-3p in CRC. However, the roles of miR-328-3p in CRC growth and metastasis were unknown. In this study, we demonstrated that miR-328-3p overexpression inhibited cell proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT). The PI3K/Akt signaling pathway was also inactivated by miR-328-3p overexpression. MiR-328-3p knockdown showed the opposite effects. In addition, we confirmed that miR-328-3p directly bound to 3'UTR of Girdin and negatively regulated its expression. Girdin knockdown or treatment with PI3K inhibitor LY294002 blocked the effects of miR-328-3p inhibitor on cell proliferation, metastasis, and the PI3K/Akt signaling pathway. Moreover, pre-miR-328 decreased numbers of liver metastatic nodules, and reduced the levels of p-Akt, p-Girdin, and Girdin in metastatic tissues in liver. In conclusion, miR-328-3p may inhibit proliferation and metastasis of CRC cells by targeting Girdin and inactivating the PI3K/Akt signaling pathway. MiR-328-3p may be a novel target in cancer therapy.

Girdin knockdown promotes apoptosis in colorectal cancer via miR-29c-3p/Girdin axis

Background

In recent years, the incidence and mortality of colorectal cancer (CRC) have increased year by year among young people. Increased levels of Girdin expression predict a poor prognosis of CRC, which presents a serious threat to human health globally. Herein, we investigated the role of Girdin in CRC and explored the underlying mechanisms in CRC.

Methods

The expression of Girdin was detected in human specimens. HCT116 cells with stably expressing or knock-out Girdin protein were successfully constructed to observe the biological function of gene. Protein expression was determined by immunohistochemistry, immunofluorescence and western blot.

Results

Clinically, overexpression of Girdin was observed in the tumor tissue and poor prognosis of CRC patients. Gain-of-function and loss-of-function assays showed that Girdin promoted CRC cell proliferation in vitro. Mechanistically, Girdin knock-down significantly enhanced apoptosis, the mitochondrial membrane potential dropped, and the reactive oxygen species increased greatly. Last but not least, we analyzed the TargetScan dataset and found that Girdin was a regulated target of hsa-miR-29c-3p in CRC. Luciferase reporter assay was used to verify the interaction between hsa-miR-29c-3p and the 3’UTR of Girdin.

Conclusions

Our findings suggest that Girdin has a crucial role in CRC progression via miR-29c-3p/Girdin axis, highlighting Girdin as a therapeutic target for CRC.

Anti-Invasion and Antiangiogenic Effects of Stellettin B through Inhibition of the Akt/Girdin Signaling Pathway and VEGF in Glioblastoma Cells

Angiogenesis and invasion are highly related with tumor metastatic potential and recurrence prediction in the most aggressive brain cancer, glioblastoma multiforme (GBM). For the first time, this study reveals that marine-sponge-derived stellettin B reduces angiogenesis and invasion. We discovered that stellettin B reduces migration of glioblastoma cells by scratch wound healing assay and invasion via chamber transwell assay. Further, stellettin B downregulates Akt/Mammalian Target of Rapamycin (Akt/mTOR) and Signal transducer and activator of transcription 3 (Stat3) signaling pathways, which are essential for invasion and angiogenesis in glioblastoma. This study further demonstrates that stellettin B affects filamentous actin (F-actin) rearrangement by decreasing the cross-linkage of phosphor-Girdin (p-Girdin), which attenuates glioblastoma cell invasion. Moreover, stellettin B blocks the expression and secretion of a major proangiogenic factor, vascular endothelial growth factor (VEGF), in glioblastoma cells. Stellettin B also reduces angiogenic tubule formation in human umbilical vein endothelial cells (HUVECs). In vivo, we observed that stellettin B decreased blood vesicle formation in developmental zebrafish and suppressed angiogenesis in Matrigel plug transplant assay in mice. Decreased VEGF transcriptional expression was also found in stellettin B⁻treated zebrafish embryos. Overall, we conclude that stellettin B might be a potential antiangiogenic and anti-invasion agent for future development of therapeutic agents for cancer therapy.

Girdin/GIV regulates collective cancer cell migration by controlling cell adhesion and cytoskeletal organization

Pathological observations show that cancer cells frequently invade the surrounding stroma in collective groups rather than through single cell migration. Here, we studied the role of the actin-binding protein Girdin, a specific regulator of collective migration of neuroblasts in the brain, in collective cancer cell migration. We found that Girdin was essential for the collective migration of the skin cancer cell line A431 on collagen gels as well as their fibroblast-led collective invasion in an organotypic culture model. We provide evidence that Girdin binds to β-catenin that plays important roles in the Wnt signaling pathway and in E-cadherin-mediated cell-cell adhesion. Girdin-depleted cells displayed scattering and impaired E-cadherin-specific cell-cell adhesion. Importantly, Girdin depletion led to impaired cytoskeletal association of the β-catenin complex, which was accompanied by changes in the supracellular actin cytoskeletal organization of cancer cell cohorts on collagen gels. Although the underlying mechanism is unclear, this observation is consistent with the established role of the actin cytoskeletal system and cell-cell adhesion in the collective behavior of cells. Finally, we showed the correlation of the expression of Girdin with that of the components of the E-cadherin complex and the differentiation of human skin cancer. Collectively, our results suggest that Girdin is an important modulator of the collective behavior of cancer cells.

Girdin protein: A potential metastasis predictor associated with prognosis in lung cancer

The present study explored the relationship between Girdin protein expression and the survival rate of patients with lung carcinoma. A total of 334 lung cancer specimens, 20 benign lung disease tissue sections and 24 fresh tissues from patients with lung carcinoma were analyzed by immunohistochemistry and western blotting. Girdin protein was expressed in 130/334 (38.93%) of the cases examined. Girdin protein expression was correlated with tumor/node/metastasis stage (P<0.001), lymph node metastasis (P=0.001), distant metastasis (P<0.001) and specimen sites (P=0.034). Girdin expression was also correlated with signal transducer and activator of transcription 3 (STAT3) expression (P<0.001). Patients with high Girdin and STAT3 expression had a significantly poorer prognosis compared with those with low/high, high/low or low/low expression (P<0.001). In summary, Girdin may be a prognostic marker of lung cancer and serve as a biomarker for metastasis.

Specific inhibition of GPCR-independent G protein signaling by a rationally engineered protein

Activation of heterotrimeric G proteins by cytoplasmic nonreceptor proteins is an alternative to the classical mechanism via G protein-coupled receptors (GPCRs). A subset of nonreceptor G protein activators is characterized by a conserved sequence named the Gα-binding and activating (GBA) motif, which confers guanine nucleotide exchange factor (GEF) activity in vitro and promotes G protein-dependent signaling in cells. GBA proteins have important roles in physiology and disease but remain greatly understudied. This is due, in part, to the lack of efficient tools that specifically disrupt GBA motif function in the context of the large multifunctional proteins in which they are embedded. This hindrance to the study of alternative mechanisms of G protein activation contrasts with the wealth of convenient chemical and genetic tools to manipulate GPCR-dependent activation. Here, we describe the rational design and implementation of a genetically encoded protein that specifically inhibits GBA motifs: GBA inhibitor (GBAi). GBAi was engineered by introducing modifications in Gαi that preclude coupling to every known major binding partner [GPCRs, Gβγ, effectors, guanine nucleotide dissociation inhibitors (GDIs), GTPase-activating proteins (GAPs), or the chaperone/GEF Ric-8A], while favoring high-affinity binding to all known GBA motifs. We demonstrate that GBAi does not interfere with canonical GPCR-G protein signaling but blocks GBA-dependent signaling in cancer cells. Furthermore, by implementing GBAi in vivo, we show that GBA-dependent signaling modulates phenotypes during Xenopus laevis embryonic development. In summary, GBAi is a selective, efficient, and convenient tool to dissect the biological processes controlled by a GPCR-independent mechanism of G protein activation mediated by cytoplasmic factors.

Silencing the Girdin gene enhances radio-sensitivity of hepatocellular carcinoma via suppression of glycolytic metabolism. J Exp Clin Cancer Res. 2017;36:110. [PMID: 28810896 PMCID: PMC5558715 DOI: 10.1186/s13046-017-0580-7]

Background

Radiotherapy has been used increasingly to treat primary hepatocellular carcinoma. Clinically, the main cause of radiotherapy failure is cellular radioresistance, conferred via glycolytic metabolism. Our previous study demonstrated that Girdin is upregulated in primary hepatocellular carcinoma and promotes the invasion and metastasis of tumor cells. However, whether Girdin underlies the radio-sensitivity of hepatocellular carcinoma remains unclear.

Methods

A short hairpin RNA (shRNA) was used to silence CCDC88A (encoding Girdin), and real-time PCR was performed to determine CCDC88A mRNA expression. Then, cell proliferation, colony formation, flow cytometric, scratch, and transwell assays were to examine the influence of Girdin silencing on cellular radiosensitivity. Glycolysis assays were conducted to exam cell glycolysis process. Western blotting was performed to explore the signaling pathway downstream of Girdin. Finally, animal experiments were performed to demonstrate the effect of CCDC88A silencing on the radiosensitivity of hepatoma in vivo.

Results

shRNA-induced Girdin silencing suppressed glycolysis and enhanced the radio-sensitivity of hepatic cell lines, HepG2 and Huh-7. Furthermore, silencing of Girdin inhibited the PI3K/AKT/HIF-1α signaling pathway, which is a central regulator of glycolysis.

Conclusion

Girdin can regulate glycolysis in hepatocellular carcinoma cells through the PI3K/AKT/HIF-1α signaling pathway, which decreases the sensitivity of tumor cells to radiotherapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-017-0580-7) contains supplementary material, which is available to authorized users.

Girdin protein expression is associated with poor prognosis in patients with invasive breast cancer

Girdin is an actin-binding Akt substrate that is an integral component of the PI3K/Akt signalling pathway. However, the clinicopathological significance of Girdin expression in breast cancer has not been clarified. The purpose of this study was to characterise the clinicopathological implication of Girdin expression in breast cancer. Immunohistochemistry-based protein expression analyses of 892 human breast cancer tissues showed that Girdin was expressed in 289 (32.4%) cases. Girdin expression was significantly associated with larger tumour size, frequent lymph node invasion, advanced cancer stage, and expression of oestrogen and progesterone receptors. Patients who had breast cancer with Girdin expression experienced significantly poorer overall survival (OS) (p=0.021) and disease-free survival (DFS) (p=0.002) than those without Girdin expression. In subtype analyses, Girdin expression was significantly correlated with poorer OS and DFS in HER2 subtype (p=0.004 and p=0.034, respectively). In triple negative breast cancer (TNBC) subtype, Girdin expression was significantly correlated with poorer DFS (p=0.035), and there was a trend toward poorer OS (p=0.060) in TNBC patients with Girdin expression. Multivariate analysis revealed that Girdin expression was an independent prognostic factor for OS (p=0.022) and DFS (p=0.030) in patients with breast cancer. In HER2 subtype under multivariate analysis, Girdin expression retained its role as an independent prognostic predictor for worse OS (p=0.023), and there was a trend toward poorer DFS (p=0.086) in patients with HER2 subtype expressing Girdin. Girdin expression may serve as a useful prognostic factor for invasive breast cancer, especially for the HER2 subtype.

Tyrosine Phosphorylation of an Actin-Binding Protein Girdin Specifically Marks Tuft Cells in Human and Mouse Gut

Tuft cells (TCs) are minor components of gastrointestinal epithelia, characterized by apical tufts and spool-shaped somas. The lack of reliable TC-markers has hindered the elucidation of its role. We developed site-specific and phosphorylation-status-specific antibodies against Girdin at tyrosine-1798 (pY1798) and found pY1798 immunostaining of mouse jejunum clearly depicted epithelial cells closely resembling TCs. This study aimed to validate pY1798 as a TC-marker. Double-fluorescence staining of intestines was performed with pY1798 and known TC-markers, for example, hematopoietic-prostaglandin-D-synthase (HPGDS), or doublecortin-like kinase 1 (DCLK1). Odds ratios (ORs) were calculated from cell counts to determine whether two markers were attracting (OR<1) or repelling (OR>1). In consequence, pY1798 signals strongly attracted those of known TC-markers. ORs for HPGDS in mouse stomach, small intestine, and colon were 0 for all, and 0.08 for DCLK1 in human small intestine. pY1798-positive cells in jejunum were distinct from other minor epithelial cells, including goblet, Paneth, and neuroendocrine cells. Thus, pY1798 was validated as a TC-marker. Interestingly, apoptosis inducers significantly increased relative TC frequencies despite the absence of proliferation at baseline. In conclusion, pY1798 is a novel TC-marker. Selective tyrosine phosphorylation and possible resistance to apoptosis inducers implied the activation of certain kinase(s) in TCs, which may become a clue to elucidate the enigmatic roles of TCs. .

Scutellarin suppresses migration and invasion of human hepatocellular carcinoma by inhibiting the STAT3/Girdin/Akt activity

Scutellarin is an active flavone from Erigeron breviscapine (vant) Hand Mass. This study aimed to investigate the potential role of scutellarin in migration and invasion of human hepatocellular carcinoma (HCC) cells and its possible mechanism. In comparison with the vehicle-treated controls, treatment with scutellarin (50 mg/kg/day) for 35 days significantly mitigated the lung and intrahepatic metastasis of HCC tumors in vivo. Scutellarin treatment significantly reduced HepG2 cell viability in a dose-dependent manner, and inhibited migration and invasion of HCC cells in vitro. Scutellarin treatment significantly reduced STAT3 and Girders of actin filaments (Girdin) expression, STAT3 and Akt phosphorylation in HCC cells. Introduction of STAT3 overexpression restored the scutellarin-downregulated Girdin expression, Akt activation, migration and invasion of HCC cells. Furthermore, induction of Girdin overexpression completely abrogated the inhibition of scutellarin on the Akt phosphorylation, migration and invasion of HCC cells. Scutellarin can inhibit HCC cell metastasis in vivo, and migration and invasion in vitro by down-regulating the STAT3/Girdin/Akt signaling.

[PKB/Akt regulates the aggregation of actin by Girdin in mouse fertilized eggs]

The purpose of this study is to reveal the role of Girdin in regulating the aggregation of actin filaments by studying the relationship between PKB/Akt and Girdin. First we used Scansite software (http://scansite.mit.edu) to predict relevant target sites of PKB/Akt on mouse Girdin. To gain insight into the role of phosphorylation of Girdin by PKB/Akt, we assessed the location of phosphorylated Girdin in fertilized eggs by staining with anti-P-Girdin 1 417 Ab. We detected a distinct increase in the fluorescence signal of F-actin and P-Girdin 1 417 after microinjection of Akt WT and myr-Akt. The addition of myr-Akt induced phosphorylation of Girdin in mouse fertilized eggs. In addition, siRNA-mediated Akt-knockdown blocked phosphorylation of Girdin. The distribution of actin filaments was obviously scattered. These results strongly suggest that PKB/Akt could directly phosphorylate Girdin on Ser1 417 and promote its function in mouse fertilized eggs.

Heterotrimeric G proteins as emerging targets for network based therapy in cancer: End of a long futile campaign striking heads of a Hydra

Most common diseases, e.g., cancer are driven by not one, but multiple cell surface receptors that trigger and sustain a pathologic signaling network. The largest fraction of therapeutic agents that target individual receptors/pathways eventually fail due to the emergence of compensatory mechanisms that reestablish the pathologic network. Recently, a rapidly emerging paradigm has revealed GIV/Girdin as a central platform for receptor cross-talk which integrates signals downstream of a myriad of cell surface receptors, and modulates several key pathways within downstream signaling network, all via non-canonical activation of trimeric G proteins. Unlike canonical signal transduction via G proteins, which is spatially and temporally restricted, the temporal and spatial features of non-canonical activation of G protein via GIV is unusually unrestricted. Consequently, the GIV●G protein interface serves as a central hub allowing for control over several pathways within the pathologic signaling network, all at once. The relevance of this new paradigm in cancer and other disease states and the pros and cons of targeting the GIV●G protein interface are discussed.

Collective invasion of cancer: Perspectives from pathology and development

Clinical pathologists have long been aware that in many types of human malignant tumors, the cells are often connected and form groups of various sizes or "nests". In this way, they achieve "collective invasion" into the surrounding stroma, rather than spreading out individually. Such collective behavior is also a common feature of migration during embryonic and postnatal developmental stages, suggesting there are advantages gained by collective cell migration in the organisms. Recent studies have revealed the mechanisms underlying the collective invasion of cancer cells. These mechanisms differ from those observed in the migration of single cells in culture, including reliance on the epithelial-mesenchymal transition program. Whereas intercellular adhesion appears to be coordinated, cancer cell groups can be heterogenous, including cells that are leaders and those that are followers. There is also interaction with the tumor microenvironment that is a prerequisite for collective invasion of cancer. In this review, we describe recently emerging mechanisms underlying the collective migration of cells, with a particular focus in our studies on the actin-binding protein Girdin/GIV and the transcriptional regulator tripartite motif containing 27. These studies provide new perspectives on the mechanistic analogy between cancer and development.

Girdin expression in cervical carcinoma and its role in the malignant properties of HeLa cells

Cervical cancer is a major cause of mortality in females worldwide, with the majority of cases reported in developing countries. The molecular mechanisms of this disease are unclear. However, increasing evidence indicates that the expression or overexpression of Girdin is associated with a poor prognosis in a variety of cancer types. Therefore, the aim of the current study was to evaluate the potential association between Girdin expression, and malignant properties of cervical cancer lesions and HeLa cells. Girdin protein expression was examined in 87 samples of cervical squamous cell lesions, including intraepithelial neoplasia (grades I and III) and invasive carcinoma, using immunohistochemical (IHC) staining. A short-hairpin RNA (shRNA) approach was employed to specifically suppress the expression of Girdin mRNA in HeLa cells in vitro, allowing the role of Girdin in a number of malignant properties to be evaluated. Girdin protein was observed in the cytoplasm of 79/87 (90.8%) cervical cancer lesion specimens. However, no positive Girdin signals were identified in healthy cervical squamous epithelium samples. Furthermore, a significant correlation between Girdin expression and lesion grade was identified (Spearman's correlation coefficient, 0.566; P<0.001). When Girdin was suppressed by Girdin shRNA, the rate of HeLa cell growth was significantly reduced in vitro (P<0.05). Additional analysis determined that Girdin was associated with serum-deprived induced HeLa apoptosis. Thus, patients with high-grade cervical cancer tumors exhibited a strong expression for Girdin, and Girdin appears to key in HeLa cell proliferation and serum-deprived induced apoptosis, supporting the hypothesis that Girdin may be important in the process of cervical carcinogenesis.

GIV/Girdin (Gα-interacting, Vesicle-associated Protein/Girdin) Creates a Positive Feedback Loop That Potentiates Outside-in Integrin Signaling in Cancer Cells

Activation of the tyrosine kinase focal adhesion kinase (FAK) upon cell stimulation by the extracellular matrix initiates integrin outside-in signaling. FAK is directly recruited to active integrins, which enhances its kinase activity and triggers downstream signaling like activation of PI3K. We recently described that Gα-interacting, vesicle-associated protein (GIV), a protein up-regulated in metastatic cancers, is also required for outside-in integrin signaling. More specifically, we found that GIV is a non-receptor guanine nucleotide exchange factor that activates trimeric G proteins in response to integrin stimulation to enhance PI3K signaling and tumor cell migration. In contrast, previous reports have established that GIV is involved in phosphotyrosine (Tyr(P))-based signaling in response to growth factor stimulation;i.e.GIV phosphorylation at Tyr-1764 and Tyr-1798 recruits and activates PI3K. Here we show that phosphorylation of GIV at Tyr-1764/Tyr-1798 is also required to enhance PI3K-Akt signaling and tumor cell migration in response to integrin stimulation, indicating that GIV functions in Tyr(P)-dependent integrin signaling. Unexpectedly, we found that activation of FAK, an upstream component of the integrin Tyr(P) signaling cascade, was diminished in GIV-depleted cells, suggesting that GIV is required to establish a positive feedback loop that enhances integrin-FAK signaling. Mechanistically, we demonstrate that this feedback activation of FAK depends on both guanine nucleotide exchange factor and Tyr(P) GIV signaling as well as on their convergence point, PI3K. Taken together, our results provide novel mechanistic insights into how GIV promotes proinvasive cancer cell behavior by working as a signal-amplifying platform at the crossroads of trimeric G protein and Tyr(P) signaling.

miR-101 Inhibiting Cell Proliferation, Migration and Invasion in Hepatocellular Carcinoma through Downregulating Girdin

miR-101 is considered to play an important role in hepato-cellular carcinoma (HCC), but the underlying molecular mechanism remains to be elucidated. Here, we aimed to confirm whether Girdin is a target gene of miR-101 and determine the tumor suppressor of miR-101 through Girdin pathway. In our previous studies, we firstly found Girdin protein was overexpressed in HCC tissues, and it closely correlated to tumor size, T stage, TNM stage and Edmondson-Steiner stage of HCC patients. After specific small interfering RNA of Girdin was transfected into HepG2 and Huh7.5.1 cells, the proliferation and invasion ability of tumor cells were significantly inhibited. In this study, we further explored the detailed molecular mechanism of Girdin in HCC. Interestingly, we found that miR-101 significantly low-expressed in HCC tissues compared with that in matched normal tissues while Girdin had a relative higher expression, and miR-101 was inversely correlated with Girdin expression. In addition, after miR-101 transfection, the proliferation, migration and invasion abilities of HepG2 cells were weakened. Furthermore, we confirmed that Girdin is a direct target gene of miR-101. Finally we confirmed Talen-mediated Girdin knockout markedly suppressed cell proliferation, migration and invasion in HCC while down-regulation of miR-101 significantly restored the inhibitory effect. Our findings suggested that miR-101/Girdin axis could be a potential application of HCC treatment.

Evolutionary Conservation of a GPCR-Independent Mechanism of Trimeric G Protein Activation

Trimeric G protein signaling is a fundamental mechanism of cellular communication in eukaryotes. The core of this mechanism consists of activation of G proteins by the guanine-nucleotide exchange factor (GEF) activity of G protein coupled receptors. However, the duration and amplitude of G protein-mediated signaling are controlled by a complex network of accessory proteins that appeared and diversified during evolution. Among them, nonreceptor proteins with GEF activity are the least characterized. We recently found that proteins of the ccdc88 family possess a Gα-binding and activating (GBA) motif that confers GEF activity and regulates mammalian cell behavior. A sequence similarity-based search revealed that ccdc88 genes are highly conserved across metazoa but the GBA motif is absent in most invertebrates. This prompted us to investigate whether the GBA motif is present in other nonreceptor proteins in invertebrates. An unbiased bioinformatics search in Caenorhabditis elegans identified GBAS-1 (GBA and SPK domain containing-1) as a GBA motif-containing protein with homologs only in closely related worm species. We demonstrate that GBAS-1 has GEF activity for the nematode G protein GOA-1 and that the two proteins are coexpressed in many cells of living worms. Furthermore, we show that GBAS-1 can activate mammalian Gα-subunits and provide structural insights into the evolutionarily conserved determinants of the GBA–G protein interface. These results demonstrate that the GBA motif is a functional GEF module conserved among highly divergent proteins across evolution, indicating that the GBA-Gα binding mode is strongly constrained under selective pressure to mediate receptor-independent G protein activation in metazoans.

Akt-dependent Girdin phosphorylation regulates repair processes after acute myocardial infarction

Myocardial infarction is a leading cause of death, and cardiac rupture following myocardial infarction leads to extremely poor prognostic feature. A large body of evidence suggests that Akt is involved in several cardiac diseases. We previously reported that Akt-mediated Girdin phosphorylation is essential for angiogenesis and neointima formation. The role of Girdin expression and phosphorylation in myocardial infarction, however, is not understood. Therefore, we employed Girdin-deficient mice and Girdin S1416A knock-in (Girdin(SA/SA)) mice, replacing the Akt phosphorylation site with alanine, to address this question. We found that Girdin was expressed and phosphorylated in cardiac fibroblasts in vitro and that its phosphorylation was crucial for the proliferation and migration of cardiac fibroblasts. In vivo, Girdin was localized in non-cardiomyocyte interstitial cells and phosphorylated in α-smooth muscle actin-positive cells, which are likely to be cardiac myofibroblasts. In an acute myocardial infarction model, Girdin(SA/SA) suppressed the accumulation and proliferation of cardiac myofibroblasts in the infarcted area. Furthermore, lower collagen deposition in Girdin(SA/SA) mice impaired cardiac repair and resulted in increased mortality attributed to cardiac rupture. These findings suggest an important role of Girdin phosphorylation at serine 1416 in cardiac repair after acute myocardial infarction and provide insights into the complex mechanism of cardiac rupture through the Akt/Girdin-mediated regulation of cardiac myofibroblasts.

Girdin-mediated interactions between cadherin and the actin cytoskeleton are required for epithelial morphogenesis in Drosophila

E-cadherin-mediated cell-cell adhesion is fundamental for epithelial tissue morphogenesis, physiology and repair. E-cadherin is a core transmembrane constituent of the zonula adherens (ZA), a belt-like adherens junction located at the apicolateral border in epithelial cells. The anchorage of ZA components to cortical actin filaments strengthens cell-cell cohesion and allows for junction contractility, which shapes epithelial tissues during development. Here, we report that the cytoskeletal adaptor protein Girdin physically and functionally interacts with components of the cadherin-catenin complex during Drosophila embryogenesis. Fly Girdin is broadly expressed throughout embryonic development and enriched at the ZA in epithelial tissues. Girdin associates with the cytoskeleton and co-precipitates with the cadherin-catenin complex protein α-Catenin (α-Cat). Girdin mutations strongly enhance adhesion defects associated with reduced DE-cadherin (DE-Cad) expression. Moreover, the fraction of DE-Cad molecules associated with the cytoskeleton decreases in the absence of Girdin, thereby identifying Girdin as a positive regulator of adherens junction function. Girdin mutant embryos display isolated epithelial cell cysts and rupture of the ventral midline, consistent with defects in cell-cell cohesion. In addition, loss of Girdin impairs the collective migration of epithelial cells, resulting in dorsal closure defects. We propose that Girdin stabilizes epithelial cell adhesion and promotes morphogenesis by regulating the linkage of the cadherin-catenin complex to the cytoskeleton.

Potential involvement of kinesin-1 in the regulation of subcellular localization of Girdin

Girdin is an actin-binding protein that has multiple functions in postnatal neural development and cancer progression. We previously showed that Girdin is a regulator of migration for neuroblasts born from neural stem cells in the subventricular zone (SVZ) and the dentate gyrus of the hippocampus in the postnatal brain. Despite a growing list of Girdin-interacting proteins, the mechanism of Girdin-mediated migration has not been fully elucidated. Girdin interacts with Disrupted-In-Schizophrenia 1 and partitioning-defective 3, both of which have been shown to interact with the kinesin microtubule motor proteins. Based on this, we have identified that Girdin also interacts with kinesin-1, a member of neuronal kinesin proteins. Although a direct interaction of Girdin and kinesin-1 has not been determined, it is of interest to find that Girdin loss-of-function mutant mice with the mutation of a basic amino acid residue-rich region (Basic mut mice) exhibit limited interaction with kinesin-1. Furthermore, expression of a kinesin-1 mutant with motor defects, leads to Girdin mislocalization. Finally, consistent with previous studies on the role of kinesin proteins in trafficking a cell-cell adhesion molecule N-cadherin, Basic mut mice showed an aberrant expression pattern of N-cadherin in migrating SVZ neuroblasts. These findings suggest a potential role of Girdin/kinesin-1 interaction in the regulation of neuroblast migration in the postnatal brain.

A Novel Approach against Vascular Intimal Hyperplasia Through the Suppression of Girdin

Intimal hyperplasia is an impediment to patency in both arteries after percutaneous angioplasty (PTA) and veingraft. It is well known that migration and proliferation of vascular smooth muscle cells (SMCs) influence the vascular remodeling process, there are no therapies to prevent intimal hyperplasia of post-PTA arteries and vein grafts. Girdin (girders of actin filaments), also known as Gα-interacting vesicle associated protein (GIV) is a novel actin-binding Akt substrate.Girdin is highly expressed in limited types of cells such as smooth muscle cells, neuroblasts, and cancer cells. Girdin is involved in the cell migration, proliferation and remodeling of actin filaments. This study revealed that Girdin is involved with intimal hyperplasia in carotid arteries after balloon injury and vein grafts and vascular SMCs migration and proliferation. There are suggestions that Girdin has pivotal roles in migration and proliferation of vascular SMCs and that gene therapy targeting Girdin could be a novel therapeutic strategy for restenosis after PTA and vein graft failure.

Regulation of epithelial cell polarity by PAR-3 depends on Girdin transcription and Girdin-Gαi3 signaling

Epithelial apicobasal polarity has fundamental roles in epithelial physiology and morphogenesis. The PAR complex, comprising PAR-3, PAR-6 and atypical protein kinase C (aPKC), is involved in determining cell polarity in various biological contexts, including in epithelial cells. However, it is not fully understood how the PAR complex induces apicobasal polarity. In this study, we found that PAR-3 regulates the protein expression of Girdin (also known as GIV or CCDC88A), a guanine-nucleotide-exchange factor (GEF) for heterotrimeric Gαi subunits, at the transcriptional level by cooperating with the AP-2 transcription factor. In addition, we confirmed that PAR-3 physically interacts with Girdin, and show that Girdin, together with the Gαi3 (also known as GNAI3), controls tight junction formation, apical domain development and actin organization downstream of PAR-3. Taken together, our findings suggest that transcriptional upregulation of Girdin expression and Girdin-Gαi3 signaling play crucial roles in regulating epithelial apicobasal polarity through the PAR complex.

Multimodular biosensors reveal a novel platform for activation of G proteins by growth factor receptors

Environmental cues are transmitted to the interior of the cell via a complex network of signaling hubs. Receptor tyrosine kinases (RTKs) and trimeric G proteins are two such major signaling hubs in eukaryotes. Conventionally, canonical signal transduction via trimeric G proteins is thought to be triggered exclusively by G protein-coupled receptors. Here we used molecular engineering to develop modular fluorescent biosensors that exploit the remarkable specificity of bimolecular recognition, i.e., of both G proteins and RTKs, and reveal the workings of a novel platform for activation of G proteins by RTKs in single living cells. Comprised of the unique modular makeup of guanidine exchange factor Gα-interacting vesicle-associated protein (GIV)/girdin, a guanidine exchange factor that links G proteins to a variety of RTKs, these biosensors provide direct evidence that RTK-GIV-Gαi ternary complexes are formed in living cells and that Gαi is transactivated within minutes after growth factor stimulation at the plasma membrane. Thus, GIV-derived biosensors provide a versatile strategy for visualizing, monitoring, and manipulating the dynamic association of Gαi with RTKs for noncanonical transactivation of G proteins in cells and illuminate a fundamental signaling event regulated by GIV during diverse cellular processes and pathophysiologic states.

Girdin phosphorylation is crucial for synaptic plasticity and memory: a potential role in the interaction of BDNF/TrkB/Akt signaling with NMDA receptor

Synaptic plasticity in hippocampal neurons has been thought to represent a variety of memories. Although accumulating evidence indicates a crucial role of BDNF/TrkB/Akt signaling in the synaptic plasticity of the hippocampus, the mechanism by which Akt, a serine/threonine kinase, controls activity-dependent neuronal plasticity remains unclear. Girdin (also known as APE, GIV, and HkRP1), an actin-binding protein involved both in the remodeling of the actin cytoskeleton and in cell migration, has been identified as a substrate of Akt. Previous studies have demonstrated that deficit of neuronal migration in the hippocampus of Girdin-deficient (Girdin(-/-)) mice is independent on serine phosphorylation of Girdin at S1416 (Girdin S1416) by Akt. In the present study, we focused on the role of Girdin S1416 phosphorylation in BDNF/TrkB/Akt signaling associated with synaptic plasticity. We found that Girdin in the hippocampus was phosphorylated at S1416 in an activity-dependent manner. Phosphorylation-deficient knock-in mice (Girdin(SA/SA) mice), in which S1416 is replaced with alanine, exhibited shrinkage of spines, deficit of hippocampal long-term potentiation, and memory impairment. These phenotypes of Girdin(SA/SA) mice resembled those of Girdin(+/-) mice, which have 50% loss of Girdin expression. Furthermore, Girdin interacted with Src kinase and NR2B subunit of NMDA receptor, leading to phosphorylation of the NR2B subunit and NMDA receptor activation. Our findings suggest that Girdin has two different functions in the hippocampus: Akt-independent neuronal migration and Akt-dependent NR2B phosphorylation through the interaction with Src, which is associated with synaptic plasticity in the hippocampus underlying memory formation.

Expression of Girdin in primary hepatocellular carcinoma and its effect on cell proliferation and invasion

Girdin has been proven to play a vital role in the process of proliferation, apoptosis, and invasion in various cancer cells, yet the underlying molecular mechanism in primary hepatocellular carcinoma (HCC) has not yet been clarified. Thereafter, we performed immunohistochemistry to detect the expression of Girdin in 40 primary HCC tissues and 30 matched adjacent tissues using hepatic carcinoma tissue microarray. Our data showed that the positive expression rate of Girdin in hepatocellular carcinoma tissues was 67.5%, higher than that found in adjacent tissues of 16.7% (P < 0.05). It closely correlates to tumor size, T stage, TNM stage and Edmondson-Steiner stage (P < 0.05) of HCC patients. After specific small interfering RNA of Girdin was transfected into HepG2 and Huh7.5.1 cells, the proliferation and invasion ability of tumor cells were significantly inhibited. In summary, we suggest that the oncogenic role of Girdin could provide new molecular target for the treatment of HCC.

Girdin, an actin-binding protein, is critical for migration, adhesion, and invasion of human glioblastoma cells

Girdin, an actin-binding protein, possesses versatile functions in a multitude of cellular processes. Although several studies have shown that Girdin is involved in the cell DNA synthesis, actin cytoskeleton rearrangement, and cell motility, the molecular mechanisms of Girdin in tumor development and progression remain elusive. In this study, through over-expression and siRNA experiments, we found that Girdin increased migration of LN229 human glioblastoma cells. On the other hand, reducing Girdin impaired F-actin polymerization, which is essential for cell morphogenesis and motility. Matrix metalloproteinase 2, critical in human glioma migration and invasion, was down-regulated upon Girdin reduction and led to decreased invasion in vitro and in vivo. In addition, silencing Girdin expression impaired the phosphorylation of two important adhesion molecules, integrin β1 and focal adhesion kinase, resulting in cell adhesion defects. Our immunohistochemical study on human gliomas tissue sections indicated that Girdin expression was positively related with glioma malignancy, supporting the in vitro and in vivo results from cell lines. Collectively, our findings suggest a critical role for Girdin in glioma infiltration. We show that reduction of Girdin, an actin-binding protein, leads to impaired F-actin polymerization and down-regulated expression of matrix metallopeptidase protein 2 (MMP-2), phosphorylated integrin β1, and phosphorylated focal adhesion kinase (FAK), which resulted in decreased migration, adhesion, and invasion of glioblastoma cells. Girdin was positively correlated with glioma malignancy and negatively associated with clinical prognosis, suggesting Girdin as a critical regulator in glioma infiltration.

Inhibition of Girdin enhances chemosensitivity of colorectal cancer cells to oxaliplatin

AIM: To investigate the effect of Girdin knockdown on the chemosensitivity of colorectal cancer cells to oxaliplatin and the possible mechanisms involved.

METHODS: Four siRNAs targeting Girdin were transfected into the chemoresistant colorectal cancer cell line DLD1. Real-time polymerase chain reaction (PCR) was employed to assess Girdin mRNA expression and the most effective siRNA was chosen for conversion into shRNA. Then, DLD1 cells were infected with lentiviruses expressing the Girdin shRNA and a scramble control, respectively, and Girdin mRNA and protein expression levels were assessed by real-time PCR and Western blotting. Furthermore, microarray experiments were used to assess global gene expression profile after Girdin suppression in DLD1 cells. Finally, the cytotoxic effect of simultaneous treatment with oxaliplatin and adriamycin (an inhibitor of a significantly downregulated gene after Girdin suppression in DLD1 cells) was examined by MTT assay.

RESULTS: The most effective siRNA suppressed Girdin expression with an inhibition efficiency of 57%. Compared with the scramble control, DLD1 cells infected with the Girdin shRNA displayed decreased Girdin mRNA and protein levels (P < 0.05), and Girdin knockdown significantly enhanced chemosensitivity to oxaliplatin in colorectal cancer cells (P < 0.05). Microarray data revealed that 381 and 162 genes were upregulated and downregulated in response to Girdin reduction, respectively, with ratios > 1.2 or < 0.8 (P < 0.01). Interestingly, TOP2B (DNA topoisomerase 2-β) was downregulated (ratio = 0.78, P = 0.0001) and oxaliplatin/adriamycin combination resulted in increased cell death compared with treatments with individual agents (P < 0.05).

CONCLUSION: Girdin knockdown enhances chemosensitivity of colorectal cancer cells to oxaliplatin via TOP2B down-regulation. These findings provide a promising approach to overcome the chemoresistance of colorectal cancer cells.

Clinical significance of Girdin expression detected by immunohistochemistry in non-small cell lung cancer

Girdin protein has been implicated in cell migration and proliferation control. Previous evidence has confirmed that Girdin is a pivotal protein during cancer progression. To date, no evidence has been identified for the clinical significance of Girdin expression in non-small cell lung cancer (NSCLC). The current study aimed to investigate the expression and clinical significance of Girdin protein in NSCLC. In total, 36 tumor samples were obtained from patients undergoing surgery for NSCLC at The 309th Hospital of Chinese People’s Liberation Army (Beijing, China). The protein expression of Girdin was determined by immunohistochemistry analysis and the levels of Girdin protein were significantly higher in tumor samples than in distal normal lung tissue. A significant correlation was identified between Girdin overexpression and blood vessel infiltration of the tumor (P=0.013). Furthermore, analysis found that the Girdin-high phenotype was not associated with higher Ki-67 score. Girdin protein was frequently overexpressed in NSCLC and expression of Girdin was associated with blood vessel infiltration. The results of the present study suggest that Girdin should be considered as a potential marker for the prognosis of NSCLC; however, future studies are required to confirm theses results.

The Akt substrate Girdin is a regulator of insulin signaling in myoblast cells

Akt kinases are important mediators of the insulin signal, and some Akt substrates are directly involved in glucose homeostasis. Recently, Girdin has been described as an Akt substrate that is expressed ubiquitously in mammals. Cells overexpressing Girdin show an enhanced Akt activity. However, not much is known about Girdin's role in insulin signaling. We therefore analyzed the role of Girdin in primary human myotubes and found a correlation between Girdin expression and insulin sensitivity of the muscle biopsy donors, as measured by a hyperinsulinemic-euglycemic clamp. To understand this finding on a cellular level, we then investigated the function of Girdin in C2C12 mouse myoblasts. Girdin knock-down reduced Akt and insulin receptor substrate-1 phosphorylation. In contrast, stable overexpression of Girdin in C2C12 cells strikingly increased insulin sensitivity through a massive upregulation of the insulin receptor and enhanced tyrosine phosphorylation of insulin receptor substrate-1. Furthermore, Akt and c-Abl kinases were constitutively activated. To investigate medium-term insulin responses we measured glucose incorporation into glycogen. The Girdin overexpressing cells showed a high basal glycogen synthesis that peaked already at 1nM insulin. Taken together, we characterized Girdin as a new and major regulator of the insulin signal in myoblasts and skeletal muscle.

Clinical implications of Girdin and PI3K protein expression in breast cancer

The aim of this study was to investigate the correlation between Girdin and PI3K in breast cancer stem cells and the clinical implications of the co-expression of these two proteins in breast cancer patients. CD44⁺/CD24⁻ tumor cells from the MD-231 cell line were sorted by flow cytometry. The expression status of Girdin and PI3K proteins was detected using western blotting and immunohistochemical staining. The relationship between Girdin and PI3K proteins and clinicopathological parameters was analyzed in 820 breast cancer patients. Girdin and PI3K proteins were more highly expressed in CD44⁺/CD24⁻ tumor stem cells compared to the control group and Girdin and PI3K proteins were co-immunoprecipitated in the MD-231 cell line. Of the 820 enrolled breast cancer patients, Girdin and PI3K proteins were expressed in 295 (35.98%) and 492 (60.00%) cases, respectively. There were 162 (19.76%) cases which co-expressed Girdin and PI3K proteins. Univariate and multivariate analyses indicated that the co-expression of Girdin and PI3K proteins correlated with histological type, metastatic nodes and distant metastasis (P=0.01, 0.001 and 0.001, respectively). After analyzing survival rates, cases with Girdin and PI3K co-expression were shown to attain a significantly increased distant metastasis rate and poorer postoperative, disease-specific survival compared to those with Girdin and PI3K co-expression (P=0.001). In the Cox regression test, Girdin and PI3K co-expression was detected as an independent prognostic factor (P=0.001). Girdin may regulate the biological behavior of breast cancer via the PI3K/Akt/mTOR pathway, and thus, serve as a potential new target for breast cancer treatment.