Increased expression of GEF-H1 promotes colon cancer progression by RhoA signaling

Regulation of the RhoA exchange factor GEF-H1 by profibrotic stimuli through a positive feedback loop involving RhoA, MRTF, and Sp1

RhoA and its effectors, the transcriptional coactivators myocardin-related transcription factor (MRTF) and serum response factor (SRF), control epithelial phenotype and are indispensable for profibrotic epithelial reprogramming during fibrogenesis. Context-dependent control of RhoA and fibrosis-associated changes in its regulators, however, remain incompletely characterized. We previously identified the guanine nucleotide exchange factor GEF-H1 as a central mediator of RhoA activation in renal tubular cells exposed to inflammatory or fibrotic stimuli. Here we found that GEF-H1 expression and phosphorylation were strongly elevated in two animal models of fibrosis. In the Unilateral Ureteral Obstruction mouse kidney fibrosis model, GEF-H1 was upregulated predominantly in the tubular compartment. GEF-H1 was also elevated and phosphorylated in a rat pulmonary artery banding (PAB) model of right ventricular fibrosis. Prolonged stimulation of LLC-PK1 tubular cells with tumor necrosis factor (TNF)-α or transforming growth factor (TGF)-β1 increased GEF-H1 expression and activated a luciferase-coupled GEF-H1 promoter. Knockdown and overexpression studies revealed that these effects were mediated by RhoA, cytoskeleton remodeling, and MRTF, indicative of a positive feedback cycle. Indeed, silencing endogenous GEF-H1 attenuated activation of the GEF-H1 promoter. Of importance, inhibition of MRTF using CCG-1423 prevented GEF-H1 upregulation in both animal models. MRTF-dependent increase in GEF-H1 was prevented by inhibition of the transcription factor Sp1, and mutating putative Sp1 binding sites in the GEF-H1 promoter eliminated its MRTF-dependent activation. As the GEF-H1/RhoA axis is key for fibrogenesis, this novel MRTF/Sp1-dependent regulation of GEF-H1 abundance represents a potential target for reducing renal and cardiac fibrosis.NEW & NOTEWORTHY We show that expression of the RhoA regulator GEF-H1 is upregulated in tubular cells exposed to fibrogenic cytokines and in animal models of kidney and heart fibrosis. We identify a pathway wherein GEF-H1/RhoA-dependent MRTF activation through its noncanonical partner Sp1 upregulates GEF-H1. Our data reveal the existence of a positive feedback cycle that enhances Rho signaling through control of both GEF-H1 activation and expression. This feedback loop may play an important role in organ fibrosis.

MiR-4646-5p Acts as a Tumor-Suppressive Factor in Triple Negative Breast Cancer and Targets the Cholesterol Transport Protein GRAMD1B

MicroRNAs (miRNAs) are crucial post-transcriptional regulators of gene expression, and their deregulation contributes to many aspects of cancer development and progression. Thus, miRNAs provide insight into oncogenic mechanisms and represent promising targets for new therapeutic approaches. A type of cancer that is still in urgent need of improved treatment options is triple negative breast cancer (TNBC). Therefore, we aimed to characterize a novel miRNA with a potential role in TNBC. Based on a previous study, we selected miR-4646-5p, a miRNA with a still unknown function in breast cancer. We discovered that higher expression of miR-4646-5p in TNBC patients is associated with better survival. In vitro assays showed that miR-4646-5p overexpression reduces growth, proliferation, and migration of TNBC cell lines, whereas inhibition had the opposite effect. Furthermore, we found that miR-4646-5p inhibits the tube formation ability of endothelial cells, which may indicate anti-angiogenic properties. By whole transcriptome analysis, we not only observed that miR-4646-5p downregulates many oncogenic factors, like tumor-promoting cytokines and migration- and invasion-related genes, but were also able to identify a direct target, the GRAM domain-containing protein 1B (GRAMD1B). GRAMD1B is involved in cellular cholesterol transport and its knockdown phenocopied the growth-reducing effects of miR-4646-5p. We thus conclude that GRAMD1B may partly contribute to the diverse tumor-suppressive effects of miR-4646-5p in TNBC.

Construction of a combined random forest and artificial neural network diagnosis model to screening potential biomarker for hepatoblastoma

PURPOSE

The purpose of our study is to identify potential biomarkers of hepatoblastoma (HB) and further explore the pathogenesis of it.

METHODS

Differentially expressed genes (DEGs) were incorporated into the combined random forest and artificial neural network diagnosis model to screen candidate genes for HB. Gene set enrichment analysis (GSEA) was used to analyze the ARHGEF2. Student's t test was performed to evaluate the difference of tumor-infiltrating immune cells (TIICs) between normal and HB samples. Spearson correlation analysis was used to calculate the correlation between ARHGEF2 and TIICs.

RESULTS

ARHGEF2, TCF3, TMED3, STMN1 and RAVER2 were screened by the new model. The GSEA of ARHGEF2 included cell cycle pathway and antigen processing presenting pathway. There were significant differences in the composition of partial TIICs between HB and normal samples (p < 0.05). ARHGEF2 was significantly correlated with memory B cells (Cor = 0.509, p < 0.05).

CONCLUSION

These 5 candidate genes contribute to the molecular diagnosis and targeted therapy of HB. And we found "ARHGEF2-RhoA-Cyclin D1/CDK4/CDK6-EF2" is a key mechanism regulating cell cycle pathway in HB. This will be helpful in the treatment of HB. The occurrence of HB is related to abnormal TIICs. We speculated that memory B cells play an important role in HB.

Therapeutic Validation of GEF-H1 Using a De Novo Designed Inhibitor in Models of Retinal Disease

Inflammation and fibrosis are important components of diseases that contribute to the malfunction of epithelia and endothelia. The Rho guanine nucleotide exchange factor (GEF) GEF-H1/ARHGEF-2 is induced in disease and stimulates inflammatory and fibrotic processes, cell migration, and metastasis. Here, we have generated peptide inhibitors to block the function of GEF-H1. Inhibitors were designed using a structural in silico approach or by isolating an inhibitory sequence from the autoregulatory C-terminal domain. Candidate inhibitors were tested for their ability to block RhoA/GEF-H1 binding in vitro, and their potency and specificity in cell-based assays. Successful inhibitors were then evaluated in models of TGFβ-induced fibrosis, LPS-stimulated endothelial cell-cell junction disruption, and cell migration. Finally, the most potent inhibitor was successfully tested in an experimental retinal disease mouse model, in which it inhibited blood vessel leakage and ameliorated retinal inflammation when treatment was initiated after disease diagnosis. Thus, an antagonist that blocks GEF-H1 signaling effectively inhibits disease features in in vitro and in vivo disease models, demonstrating that GEF-H1 is an effective therapeutic target and establishing a new therapeutic approach.

N6-Methyladenosine Reader YTHDF1 Promotes ARHGEF2 Translation and RhoA Signaling in Colorectal Cancer

BACKGROUND & AIMS

N6-methyladenosine (m⁶A) governs the fate of RNAs through m⁶A readers. Colorectal cancer (CRC) exhibits aberrant m⁶A modifications and expression of m⁶A regulators. However, how m⁶A readers interpret oncogenic m⁶A methylome to promote malignant transformation remains to be illustrated.

METHODS

YTH N6-methyladenosine RNA binding protein 1 (Ythdf1) knockout mouse was generated to determine the effect of Ythdf1 in CRC tumorigenesis in vivo. Multiomic analysis of RNA-sequencing, m⁶A methylated RNA immunoprecipitation sequencing, YTHDF1 RNA immunoprecipitation sequencing, and proteomics were performed to unravel targets of YTHDF1 in CRC. The therapeutic potential of targeting YTHDF1-m⁶A-Rho/Rac guanine nucleotide exchange factor 2 (ARHGEF2) was evaluated using small interfering RNA (siRNA) encapsulated by lipid nanoparticles (LNP).

RESULTS

DNA copy number gain of YTHDF1 is a frequent event in CRC and contributes to its overexpression. High expression of YTHDF1 is significantly associated with metastatic gene signature in patient tumors. Ythdf1 knockout in mice dampened tumor growth in an inflammatory CRC model. YTHDF1 promotes cell growth in CRC cell lines and primary organoids and lung and liver metastasis in vivo. Integrative multiomics analysis identified RhoA activator ARHGEF2 as a key downstream target of YTHDF1. YTHDF1 binds to m⁶A sites of ARHGEF2 messenger RNA, resulting in enhanced translation of ARHGEF2. Ectopic expression of ARHGEF2 restored impaired RhoA signaling, cell growth, and metastatic ability both in vitro and in vivo caused by YTHDF1 loss, verifying that ARHGEF2 is a key target of YTHDF1. Finally, ARHGEF2 siRNA delivered by LNP significantly suppressed tumor growth and metastasis in vivo.

CONCLUSIONS

We identify a novel oncogenic epitranscriptome axis of YTHDF1-m⁶A-ARHGEF2, which regulates CRC tumorigenesis and metastasis. siRNA-delivering LNP drug validated the therapeutic potential of targeting this axis in CRC.

Oncogenic Role of Exosomal Circular and Long Noncoding RNAs in Gastrointestinal Cancers

Circular RNAs (circRNAs) and long noncoding RNAs (lncRNAs) are differentially expressed in gastrointestinal cancers. These noncoding RNAs (ncRNAs) regulate a variety of cellular activities by physically interacting with microRNAs and proteins and altering their activity. It has also been suggested that exosomes encapsulate circRNAs and lncRNAs in cancer cells. Exosomes are then discharged into the extracellular environment, where they are taken up by other cells. As a result, exosomal ncRNA cargo is critical for cell-cell communication within the cancer microenvironment. Exosomal ncRNAs can regulate a range of events, such as angiogenesis, metastasis, immune evasion, drug resistance, and epithelial-to-mesenchymal transition. To set the groundwork for developing novel therapeutic strategies against gastrointestinal malignancies, a thorough understanding of circRNAs and lncRNAs is required. In this review, we discuss the function and intrinsic features of oncogenic circRNAs and lncRNAs that are enriched within exosomes.

Exosomes: Emerging modulators of signal transduction in colorectal cancer from molecular understanding to clinical application

Exosomes are small cell derived membrane nano-vesicles that carry various components including lipids, proteins and nucleic acids. There is accumulating evidence that exosomes have a role in tumorigenesis, tumor invasiveness and metastasis. Furthermore, oncogene mutation may influence exosome release from tumor cells. Exosomes may induce colorectal cancer by altering signaling cascades such as the Wnt/β-catenin and KRAS pathways that are involved in cell proliferation, apoptosis, dissemination, angiogenesis, and drug resistance. The aim of this review was to overview recent findings evaluating the association between tumor cells-derived exosomes and their content in modulating signaling pathways in colorectal cancer.

S-1-propenylcysteine improves TNF-α-induced vascular endothelial barrier dysfunction by suppressing the GEF-H1/RhoA/Rac pathway

Background

Vascular endothelial barrier function is maintained by cell-to-cell junctional proteins and contributes to vascular homeostasis. Various risk factors such as inflammation disrupt barrier function through down-regulation of these proteins and promote vascular diseases such as atherosclerosis. Previous studies have demonstrated that aged garlic extract (AGE) and its sulfur-containing constituents exert the protective effects against several vascular diseases such as atherosclerosis. In this study, we examined whether AGE and its sulfur-containing constituents improve the endothelial barrier dysfunction elicited by a pro-inflammatory cytokine, Tumor-necrosis factor-α (TNF-α), and explored their mode of action on TNF-α signaling pathway.

Methods

Human umbilical vein endothelial cells (HUVECs) were treated with test substances in the presence of TNF-α for various time periods. The endothelial permeability was measured by using a transwell permeability assay. The localization of cell-to-cell junctional proteins and actin cytoskeletons were visualized by immunostaining. RhoA and Rac activities were assessed by using GTP-binding protein pulldown assay. Gene and protein expression levels of signaling molecules were analyzed by real-time PCR and western blotting, respectively.

Results

We found that AGE and its major sulfur-containing constituent, S-1-propenylcysteine (S1PC), reduced hyperpermeability elicited by TNF-α in HUVECs. In addition, S1PC inhibited TNF-α-induced production of myosin light chain (MLC) kinase and inactivation of MLC phosphatase through the suppression of the Rac and RhoA signaling pathways, respectively, which resulted in the dephosphorylation of MLC2, a key factor of actin remodeling. Moreover, S1PC inhibited the phosphorylation and activation of guanine nucleotide exchange factor-H1 (GEF-H1), a common upstream key molecule and activator of Rac and RhoA. These effects of S1PC were accompanied by its ability to prevent the disruption of junctional proteins on the cell–cell contact regions and the increase of actin stress fibers induced by TNF-α.

Conclusions

The present study suggested that AGE and its major constituent, S1PC, improve endothelial barrier disruption through the protection of junctional proteins on plasma membrane.

Rho GTPases as Key Molecular Players within Intestinal Mucosa and GI Diseases

Rho proteins operate as key regulators of the cytoskeleton, cell morphology and trafficking. Acting as molecular switches, the function of Rho GTPases is determined by guanosine triphosphate (GTP)/guanosine diphosphate (GDP) exchange and their lipidation via prenylation, allowing their binding to cellular membranes and the interaction with downstream effector proteins in close proximity to the membrane. A plethora of in vitro studies demonstrate the indispensable function of Rho proteins for cytoskeleton dynamics within different cell types. However, only in the last decades we have got access to genetically modified mouse models to decipher the intricate regulation between members of the Rho family within specific cell types in the complex in vivo situation. Translationally, alterations of the expression and/or function of Rho GTPases have been associated with several pathological conditions, such as inflammation and cancer. In the context of the GI tract, the continuous crosstalk between the host and the intestinal microbiota requires a tight regulation of the complex interaction between cellular components within the intestinal tissue. Recent studies demonstrate that Rho GTPases play important roles for the maintenance of tissue homeostasis in the gut. We will summarize the current knowledge on Rho protein function within individual cell types in the intestinal mucosa in vivo, with special focus on intestinal epithelial cells and T cells.

High ARHGEF2 (GEF-H1) Expression is Associated with Poor Prognosis Via Cell Cycle Regulation in Patients with Pancreatic Cancer

BACKGROUND

Pancreatic cancer has an extremely poor prognosis, even after curative resection. Treatment options for pancreatic cancer remain limited, therefore new therapeutic targets are urgently needed. We searched for genes predictive of poor prognosis in pancreatic cancer using a public database and validated the survival impact of the selected gene in a patient cohort.

METHODS

We used a public database to search for genes associated with early pancreatic cancer recurrence. As a validation cohort, 201 patients who underwent radical resection in our institution were enrolled. Expression of the target gene was evaluated using immunohistochemistry (IHC). We evaluated growth and invasiveness using small interfering RNAs, then performed pathway analysis using gene set enrichment analysis.

RESULTS

We extracted ARHGEF2 from GSE21501 as a gene with a high hazard ratio (HR) for early recurrence within 1 year. The high ARHGEF2 expression group had significantly poorer recurrence-free survival (RFS) and poorer overall survival (OS) than the low ARHGEF2 expression group. Multivariate analysis demonstrated that high ARHGEF2 expression was an independent poor prognostic factor for RFS (HR 1.92) and OS (HR 1.63). In vitro, ARHGEF2 suppression resulted in reduced cell growth and invasiveness. Bioinformatic analysis revealed that ARHGEF2 expression was associated with MYC, G2M, E2F, and CDC25A expression, suggesting that c-Myc and cell cycle genes are associated with high ARHGEF2 expression. IHC revealed a positive correlation between ARHGEF2 and c-Myc expression.

CONCLUSIONS

High ARHGEF2 expression is associated with cell cycle progression, and predicts early recurrence and poor survival in patients with pancreatic cancer.

Regulation and functions of the RhoA regulatory guanine nucleotide exchange factor GEF-H1

Since the discovery by Madaule and Axel in 1985 of the first Ras homologue (Rho) protein in Aplysia and its human orthologue RhoB, membership in the Rho GTPase family has grown to 20 proteins, with representatives in all eukaryotic species. These GTPases are molecular switches that cycle between active (GTP bound) and inactivate (GDP bound) states. The exchange of GDP for GTP on Rho GTPases is facilitated by guanine exchange factors (GEFs). Approximately 80 Rho GEFs have been identified to date, and only a few GEFs associate with microtubules. The guanine nucleotide exchange factor H1, GEF-H1, is a unique GEF that associates with microtubules and is regulated by the polymerization state of microtubule networks. This review summarizes the regulation and functions of GEF-H1 and discusses the roles of GEF-H1 in human diseases.

Pumping the brakes on RAS - negative regulators and death effectors of RAS

Mutations that activate the RAS oncoproteins are common in cancer. However, aberrant upregulation of RAS activity often occurs in the absence of activating mutations in the RAS genes due to defects in RAS regulators. It is now clear that loss of function of Ras GTPase-activating proteins (RasGAPs) is common in tumors, and germline mutations in certain RasGAP genes are responsible for some clinical syndromes. Although regulation of RAS is central to their activity, RasGAPs exhibit great diversity in their binding partners and therefore affect signaling by multiple mechanisms that are independent of RAS. The RASSF family of tumor suppressors are essential to RAS-induced apoptosis and senescence, and constitute a barrier to RAS-mediated transformation. Suppression of RASSF protein expression can also promote the development of excessive RAS signaling by uncoupling RAS from growth inhibitory pathways. Here, we will examine how these effectors of RAS contribute to tumor suppression, through both RAS-dependent and RAS-independent mechanisms.

Loss of thymidine kinase 1 inhibits lung cancer growth and metastatic attributes by reducing GDF15 expression

Metabolic alterations that are critical for cancer cell growth and metastasis are one of the key hallmarks of cancer. Here, we show that thymidine kinase 1 (TK1) is significantly overexpressed in tumor samples from lung adenocarcinoma (LUAD) patients relative to normal controls, and this TK1 overexpression is associated with significantly reduced overall survival and cancer recurrence. Genetic knockdown of TK1 with short hairpin RNAs (shRNAs) inhibits both the growth and metastatic attributes of LUAD cells in culture and in mice. We further show that transcriptional overexpression of TK1 in LUAD cells is driven, in part, by MAP kinase pathway in a transcription factor MAZ dependent manner. Using targeted and gene expression profiling-based approaches, we then show that loss of TK1 in LUAD cells results in reduced Rho GTPase activity and reduced expression of growth and differentiation factor 15 (GDF15). Furthermore, ectopic expression of GDF15 can partially rescue TK1 knockdown-induced LUAD growth and metastasis inhibition, confirming its important role as a downstream mediator of TK1 function in LUAD. Collectively, our findings demonstrate that TK1 facilitates LUAD tumor and metastatic growth and represents a target for LUAD therapy.

Thymidine kinase 1 (TK1) is overexpressed and associated with poor prognosis in a number of different cancers. However, despite these data suggesting an important role for TK1 in cancer pathogenesis, no study thus far has analyzed the functional effect of TK1 inhibition on tumor growth and metastasis. In this study, we performed TK1 knockdown and found that this protein is necessary for lung adenocarcinoma (LUAD) tumor growth and metastasis. Notably, inhibition of another nucleotide kinase, deoxycytidine kinase (DCK), had no effect on LUAD tumor growth and metastatic attributes. We therefore performed experiments to determine if the TK1 mechanism of action in cancer is distinct from its previously reported role in DNA damage, DNA replication, and DNA repair. We found that TK1 can promote LUAD tumor growth and metastasis in a non-canonical manner by activating Rho GTPase activity and growth and differentiation factor 15 (GDF15) expression. Taken together, our data suggest that TK1 may represent a potential target for development of LUAD therapy, due to its critical role in maintaining lung tumor growth and metastasis.