GTPase Activity Research Articles

Characterization of Dynamin-related proteins (DRP) in bread wheat: TaDRP1D-B as regulator of biotic and abiotic stresses

Bread wheat (Triticum aestivum) is a vital global staple food, providing 30% of the world's caloric intake and nutritional needs. It was domesticated over 10,000 years ago and adapted to various biotic and abiotic stresses, crucial for maintaining food security. Modern research highlights the interconnected signalling pathways for both biotic and abiotic stresses, that help wheat cope with these biotic and abiotic stresses. Identification of regulatory proteins is essential for advanced wheat breeding. In the current study, 32 DRP genes in wheat were identified that are evenly distributed on all the chromosomes with the presence of conserved dynamin-related domain. PPI analysis reveals that the TaDRP2-like genes interact with each other. Gene ontology analysis indicating the significant involvement of DRP genes in various processes including GTPase activity, binding, microtubule binding, and various cells including membrane (GO:0016020), cytoplasm (GO:0005737), microtubule (GO:0005874). Cis-element prediction reveals the enrichment of total 2006 elements including CAAT-box (390), TATA-box (327), MYB (131), and ABRE (93). Transcriptome and qRT-PCR analyses showed that TaDRP1-like, TaDRP2-like, and TaDRP3-like genes are highly expressed in roots, stems, leaves, and spikes, with lower expression in grains. Notably, TaDRP1D-B emerged as a potential candidate for enhancing resistance to powdery mildew, rust, drought, and heat stress. Furthermore, the interaction compatibility of TaDRP1D-B with PPA2 further confirms the potential role in regulating plant disease response. This research provides a foundation for developing strategies to enhance wheat resilience, directly contributing to global food security.

Abstract A020: Elevated extracellular glucose level in tumor microenvironment by hyperglycemia increases glycolysis rate, stiffness, contractility, and motility of breast cancer cells through the cAMP-RhoA-Rock and AMPK-YAP-RhoA axes to promote metastasis

Abstract Glucose is a preferred nutrient for most cells, including cancer cells. The tumor microenvironment is both hypoxic and hypoglycemic. Glucose levels in tumors are ten times lower than in normal tissues due to poor vascularization and high glucose consumption by cancer cells, which adapt to hypoglycemia. Obesity, often accompanied by hyperglycemia, hyperinsulinemia, and hypertriglyceridemia, is linked to increased breast cancer metastasis. High extracellular glucose levels have been shown to promote cancer cell motility, though the mechanisms remain unclear. Given cancer cells' reliance on aerobic glycolysis (the Warburg effect), we hypothesized that hyperglycemia in obesity promotes cancer metastasis by modulating glucose metabolism and related cell mechanics pathways. Using Triple-Negative Breast Cancer (TNBC) cells, we found that elevated extracellular glucose levels increase glycolysis, activating the RhoA GTPase signaling pathway. This results in greater cell stiffness and contractility, correlating with increased motility. Our unpublished data, which I will present, validate these findings in obese-TNBC mouse models and further elucidate the glycolysis-mediated activation of the RhoA-ROCK axis. We also identified a novel long-term effect of hyperglycemia in promoting metastasis via transcriptional regulation of the AMPK-YAP-RhoA axis. To confirm hyperglycemia's pro-metastatic effects, we developed two obese-TNBC mouse models using diet-induced obesity (DIO) in NSG and C57BL/6J mice with orthotopic implantation of human and mouse TNBC cells, respectively. RhoA GTPase activity was measured with a GTP-RhoA FRET sensor or pull-down assay. Cell stiffness was assessed using our innovative parallel microfiltration (PMF) assay or Atomic Force Microscopy (AFM). We disrupted glucose uptake by knocking out glucose transporter 3 (GLUT3) via CRISPR/Cas9 or using a GLUT3-selective inhibitor, G3iA. Cell motility was measured by scratch wound-healing and invasion assays. Bulk RNA-seq identified differentially expressed genes under high glucose conditions in human breast cancer cells. Our results show increased lung metastasis of breast cancer cells under hyperglycemic conditions in vivo. Besides the previously reported cAMP-RhoA-ROCK axis, we discovered the glycolysis-AMPK-YAP axis also regulates RhoA-ROCK activity transcriptionally. GLUT3 inhibition activated AMPK, reduced F-actin levels via the AMPK-VASP axis, and decreased non-muscle myosin activity through the AMPK-YAP-RhoA axis. These changes in cell mechanics correlated with reduced motility. Our study suggests that targeting glucose metabolism and cell mechanics could be a novel approach to inhibit cancer metastasis, particularly in obese patients. Citation Format: Tae-Hyung Kim, Aadil Q Bhat, Jun-Yong Choe, Donghoon Yoon. Elevated extracellular glucose level in tumor microenvironment by hyperglycemia increases glycolysis rate, stiffness, contractility, and motility of breast cancer cells through the cAMP-RhoA-Rock and AMPK-YAP-RhoA axes to promote metastasis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor-body Interactions: The Roles of Micro- and Macroenvironment in Cancer; 2024 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2024;84(22_Suppl):Abstract nr A020.

An allosteric inhibitor of RhoGAP class-IX myosins suppresses the metastatic features of cancer cells.

Aberrant Ras homologous (Rho) GTPase signalling is a major driver of cancer metastasis, and GTPase-activating proteins (GAPs), the negative regulators of RhoGTPases, are considered promising targets for suppressing metastasis, yet drug discovery efforts have remained elusive. Here, we report the identification and characterization of adhibin, a synthetic allosteric inhibitor of RhoGAP class-IX myosins that abrogates ATPase and motor function, suppressing RhoGTPase-mediated modes of cancer cell metastasis. In human and murine adenocarcinoma and melanoma cell models, including three-dimensional spheroid cultures, we reveal anti-migratory and anti-adhesive properties of adhibin that originate from local disturbances in RhoA/ROCK-regulated signalling, affecting actin-dynamics and actomyosin-based cell-contractility. Adhibin blocks membrane protrusion formation, disturbs remodelling of cell-matrix adhesions, affects contractile ring formation, and disrupts epithelial junction stability; processes severely impairing single/collective cell migration and cytokinesis. Combined with the non-toxic, non-pathological signatures of adhibin validated in organoids, mouse and Drosophila models, this mechanism of action provides the basis for developing anti-metastatic cancer therapies.

Regulation and functions of the DLC family of RhoGAP proteins: Implications for development and cancer.

The DLC (Deleted in Liver Cancer) family of RhoGAP (Rho GTPase-activating) proteins has been extensively studied since the identification of the first family member nearly 30 years ago. Rho GTPase signaling is essential for various cellular processes, including cytoskeletal dynamics, cell migration, and proliferation. Members of the DLC family are key regulators of this signaling pathway, with well-established roles in development and carcinogenesis. Here, we provide a comprehensive review of research into DLC regulation and cellular functions over the last three decades. In particular, we summarize control mechanisms of DLC gene expression at both the transcriptional and post-transcriptional level. Additionally, recent advances in understanding the post-translational regulation of DLC proteins that allow for tuning of protein activity and localization are highlighted. This detailed overview will serve as resource for future studies aimed at further elucidating the complex regulatory mechanisms of DLC family proteins and exploring their potential as targets for therapeutic applications.

TMOD-12. DEFINING THE ROLE OF THE DAAM2 R414W GERMLINE VARIANT IN FAMILIAL GLIOMA

Abstract Malignant glioma is the most common primary brain tumor in adults, leading to high morbidity and mortality due to its aggressive nature and limited efficacious treatment options. To improve this prognosis, research has focused on genetic factors that may contribute to glioma. While most glioma cases arise from sporadic somatic mutations, approximately 5-10% are classified as familial glioma, stemming from inherited genetic variations. Although several studies have explored mechanisms behind somatic mutations in glioma, less is known about hereditary variants that promote glioma susceptibility. We recently discovered five germline mutations in Daam2 (Dishevelled associated activator of morphogenesis 2) from familial glioma patients. To examine the role of these mutations in familial glioma, we overexpressed these mutations in patient-derived glioma stem-like cells, which were subsequently orthotopically xenografted into immunodeficient mice. We identified that one of these mutations, Daam2-R414W, promotes tumor cell proliferation both in vitro and in vivo. To further understand the role of the Daam2-R414W mutation in familial glioma, we generated a knock-in immunocompetent mouse model with the Daam2-R414W mutation. In these mutant mice, we found an increased number of proliferating glial progenitor cells in the subventricular zone compared to Daam2 wildtype mice, suggesting the potential of the Daam2-R414W mutation to influence glial progenitor expansion to stimulate glioma initiation. Furthermore, to establish a potential mechanism, we performed proteomic profiling of Daam2 wildtype and Daam2-R414W overexpression tumors and found enrichment of Git1, a GTPase-activating protein involved in cytoskeletal remodeling, suggesting that the Daam2-R414W variant may interact with Git1 to promote tumor invasion. Our findings thus far identify a hereditary genetic variant with the potential to increase the risk of glioma, shedding light on the repercussions of a human developmental gene variant and its potential to disrupt normal cellular machinery to promote malignancy and glioma development.

β2-Chimaerin, a GTPase-Activating Protein for Rac1, Is a Novel Regulator of Hepatic Insulin Signaling and Glucose Metabolism

Glucose homeostasis is a complex process regulated by multiple organs and hormones, with insulin playing a central role. Recent evidence underscores the role of small GTP-binding proteins, particularly Rac1, in regulating insulin secretion and glucose uptake. However, the role of Rac1-regulatory proteins in these processes remains largely unexplored. In this study, we investigated the role of β2-chimaerin, a Rac1-specific GTPase-activating protein (GAP), in glucose homeostasis using whole-body β2-chimaerin knockout mice. Our data revealed that β2-chimaerin deficiency results in improved glucose tolerance and enhanced insulin sensitivity in mice. These metabolic effects were associated with increased insulin-induced AKT phosphorylation in the liver and activation of downstream pathways that regulate gluconeogenesis and glycogen synthesis. We show that insulin activates Rac1 in the liver. However, β2-chimaerin deletion did not significantly alter Rac1 activation in this organ, suggesting that β2-chimaerin regulates insulin signaling via a Rac1-independent mechanism. These findings expand our understanding of Rac1 regulation in glucose metabolism, and identify β2-chimaerin as a novel modulator of hepatic insulin signaling, with potential implications for the development of insulin resistance and diabetes.

Antagonistic Effects of Actin-Specific Toxins on Salmonella Typhimurium Invasion into Mammalian Cells

Competition between bacterial species is a major factor shaping microbial communities. It is possible but remains largely unexplored that competition between bacterial pathogens can be mediated through antagonistic effects of bacterial effector proteins on host systems, particularly the actin cytoskeleton. Using Salmonella Typhimurium invasion into cells as a model, we demonstrate that invasion is inhibited if the host actin cytoskeleton is disturbed by actin-specific toxins, namely, Vibrio cholerae MARTX actin crosslinking (ACD) and Rho GTPase inactivation (RID) domains, Photorhabdus luminescens TccC3, and Salmonella’s own SpvB. We noticed that ACD, being an effective inhibitor of tandem G-actin-binding assembly factors, is likely to inhibit the activity of another Vibrio effector, VopF. In reconstituted actin polymerization assays and by live-cell microscopy, we confirmed that ACD potently halted the actin nucleation and pointed-end elongation activities of VopF, revealing competition between these two V. cholerae effectors. These results suggest that bacterial effectors from different species that target the same host machinery or proteins may represent an effective but largely overlooked mechanism of indirect bacterial competition in host-associated microbial communities. Whether the proposed inhibition mechanism involves the actin cytoskeleton or other host cell compartments, such inhibition deserves investigation and may contribute to a documented scarcity of human enteric co-infections by different pathogenic bacteria.

ASAP1 and ARF1 regulate myogenic differentiation in rhabdomyosarcoma by modulating TAZ activity.

Despite aggressive, multimodal therapies, the prognosis of patients with refractory or recurrent rhabdomyosarcoma (RMS) has not improved in four decades. Because RMS resembles skeletal muscle precursor cells, differentiation-inducing therapy has been proposed for patients with advanced disease. In RAS-mutant PAX fusion-negative RMS (FN-FMS) preclinical models, MEK1/2 inhibition (MEKi) induces differentiation, slows tumor growth, and extends survival. However, the response is short-lived. A better understanding of the molecular mechanisms regulating FN-RMS differentiation could improve differentiation therapy. Here, we identified a role in FN-RMS differentiation for ASAP1, an ARF GTPase-activating protein (ARF GAP) with both pro-invasive and tumor suppressor functions. We found that ASAP1 knockdown inhibited differentiation in FN-RMS cells. Interestingly, knockdown of the GTPases ARF1 or ARF5, targets of ASAP1 GAP activity, also blocked differentiation of FN-RMS. We discovered that loss of ARF pathway components blocked myogenic transcription factor expression. Therefore, we examined the effects on transcriptional regulators. MEKi led to the phosphorylation and inactivation of WWTR1 (TAZ), a homolog of the pro-proliferative transcriptional co-activator YAP1 regulated by the Hippo pathway. However, loss of ASAP1 or ARF1 blocked this inactivation, which inhibits MEKi-induced differentiation. Finally, MEKi-induced differentiation was rescued by dual knockdown of ASAP1 and WWTR1. This study shows that ASAP1 and ARF1 are necessary for myogenic differentiation, providing a deeper understanding of differentiation in FN-RMS and illuminating an opportunity to advance differentiation therapy. Implications: ASAP1 and ARF1 regulate MEKi-induced differentiation of FN-RMS cells by modulating WWTR1 (TAZ) activity, supporting YAP1/TAZ inhibition as a FN-RMS differentiation therapy strategy.

Transcriptional Profiling of Tofacitinib Treatment in Juvenile Idiopathic Arthritis: Implications for Treatment Response Prediction.

To assess changes in gene expression following tofacitinib treatment and investigate transcription patterns as potential predictors of treatment response in patients with active juvenile idiopathic arthritis (JIA). Whole blood samples were collected from JIA patients at baseline and after 18 weeks of open-label tofacitinib treatment (clinical trial NCT02592434). Patients who achieved a JIA-American College of Rheumatology (ACR) response of 70 or above at week 18 were classified as treatment-responders (TR) while those with at most a JIA-ACR30 response were classified as poor-responders (PR). Differential gene expression and gene ontology (GO) over-representation analyses were performed to compare RNA expression between week 18 and baseline samples, as well as between PR and TR samples at baseline. Samples from 67 patients at baseline and 60 at week 18 were analyzed. Following 18 weeks of tofacitinib treatment across all JIA subjects, 883 genes showed significant differential expression (week 18 - baseline). The most strongly downregulated genes were over-represented within IL-7, type I, and type II interferon pathways, while upregulated genes were enriched in ontologies related to neuronal cell processes and cell signaling. Comparing PR and TR at baseline, 663 genes showed differential expression. Upregulated genes were over-represented within ontologies including activation of MAPK activity (p=9.40x10-5), myeloid cell development (p=8.13 x10-5), activation of GTPase activity (p=0.00015), and organelle transport along microtubules (p=0.00021). Tofacitinib treatment in JIA downregulated genes in interferon and IL-7 signaling pathways regardless of effectiveness. Furthermore, baseline upregulation of MAPK signaling may predict poor response to tofacitinib treatment in JIA.

Identification of key genes in diabetic nephropathy based on lipid metabolism.

Diabetic nephropathy (DN) is a common systemic microvascular complication of diabetes with a high incidence rate. Notably, the disturbance of lipid metabolism is associated with DN progression. The present study aimed to identify lipid metabolism-related hub genes associated with DN for improved diagnosis of DN. The gene expression profile data of DN and healthy samples (GSE142153) were obtained from the Gene Expression Omnibus database, and the lipid metabolism-related genes were obtained from the Molecular Signatures Database. Differentially expressed genes (DEGs) between DN and healthy samples were analyzed. The weighted gene co-expression network analysis (WGCNA) was performed to examine the relationship between genes and clinical traits to identify the key module genes associated with DN. Next, the Venn Diagram R package was used to identify the lipid metabolism-related genes associated with DN and their protein-protein interaction (PPI) network was constructed. Subsequently, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were performed. The hub genes were identified using machine-learning algorithms. The Gene Set Enrichment Analysis (GSEA) was used to analyze the functions of the hub genes. The present study also investigated the immune infiltration discrepancies between DN and healthy samples, and assessed the correlation between the immune cells and hub genes. Finally, the expression levels of key genes were verified by reverse transcription-quantitative (RT-q)PCR. The present study determined 1,445 DEGs in DN samples. In addition, 694 DN-related genes in MEyellow and MEturquoise modules were identified by WGCNA. Next, the Venn Diagram R package was used to identify 17 lipid metabolism-related genes and to construct a PPI network. GO analysis revealed that these 17 genes were markedly associated with 'phospholipid biosynthetic process' and 'cholesterol biosynthetic process', while the KEGG analysis showed that they were enriched in 'glycerophospholipid metabolism' and 'fatty acid degradation'. In addition, SAMD8 and CYP51A1 were identified through the intersections of two machine-learning algorithms. The results of GSEA revealed that the 'mitochondrial matrix' and 'GTPase activity' were the markedly enriched GO terms in both SAMD8 and CYP51A1. Their KEGG pathways were mainly concentrated in the 'pathways of neurodegeneration-multiple diseases'. Immune infiltration analysis showed that nine types of immune cells had different expression levels in DN (diseased) and healthy samples. Notably, SAMD8 and CYP51A1 were both markedly associated with activated B cells and effector memory CD8 T cells. Finally, RT-qPCR confirmed the high expression of SAMD8 and CYP51A1 in DN. In conclusion, lipid metabolism-related genes SAMD8 and CYP51A1 may play key roles in DN. The present study provides fundamental information on lipid metabolism that may aid the diagnosis and treatment of DN.

Structural basis for the effects of Ser387 phosphorylation of MgcRacGAP on its GTPase-activating activities for CDC42 and RHOA

MgcRacGAP is a GTPase-activating protein (GAP) for the Rho family GTPases. During cytokinesis, MgcRacGAP localizes to the midbody, where it activates the GTPase activity of Rho family GTPases to facilitate cytokinesis. In the midbody, Aurora B phosphorylates Ser387 within the GAP domain of human MgcRacGAP, a modification that is suggested to influence GTPase preference. However, there are conflicting reports, with some studies indicating that Ser387 phosphorylation does not alter the GTPase preference of MgcRacGAP. This controversy highlights the need for a deeper understanding of the molecular interactions involved, which can be clarified through structural analyses. In the present study, we determined the crystal structures of the wild-type MgcRacGAP GAP domain complexed with CDC42•GDP•AlF4− and the S378D phosphomimetic mutant GAP domain fused with RHOA•GDP•AlF4−. Additionally, crystal structures of the GAP domains were determined for the S387D and S387A mutants. Our analysis revealed that neither GTPase binding nor S387D mutation affected the overall structure of the GAP domain. However, comparison of the CDC42•MgcRacGAP (wild-type) complex with the RHOA-MgcRacGAP(S378D) fusion protein structure indicated that the S387D mutation caused positional shifts in both CDC42 and RHOA relative to MgcRacGAP. These shifts reduced interactions with CDC42 more severely than those with RHOA. In fact, the S387D mutation decreased the GTPase-activating activity of MgcRacGAP toward CDC42, while its impact on RHOA was only moderate. This difference in the rate of activity reduction may play an important role in GTPase preference.

Engineering and evolution of Yarrowia lipolytica for producing lipids from lignocellulosic hydrolysates

Yarrowia lipolytica, an oleaginous yeast, shows promise for industrial fermentation due to its robust acetyl-CoA flux and well-developed genetic engineering tools. However, its lack of an active xylose metabolism restricts the conversion of cellulosic sugars to valuable products. To address this, metabolic engineering, and adaptive laboratory evolution (ALE) were applied to the Y. lipolytica PO1f strain, resulting in an efficient xylose-assimilating strain (XEV). Whole-genome sequencing (WGS) of the XEV followed by reverse engineering revealed that the amplification of the heterologous oxidoreductase pathway and a mutation in the GTPase-activating protein gene (YALI0B12100g) might be the primary reasons for improved xylose assimilation in the XEV strain. When a sorghum hydrolysate was used, the XEV strain showed superior xylose consumption and lipid production compared to its parental strain (X123). This study advances our understanding of xylose metabolism in Y. lipolytica and proposes effective metabolic engineering strategies for optimizing lignocellulosic hydrolysates.

Pharmacologic restoration of GTP hydrolysis by mutant RAS.

Approximately 3.4 million patients worldwide are diagnosed each year with cancers that harbor pathogenic mutations in one of three RAS proto-oncogenes (KRAS, NRAS and HRAS)1,2. These mutations impair the GTPase activity of RAS, leading to activation of downstream signaling and proliferation3-6. Long-standing efforts to restore the hydrolase activity of RAS mutants have been unsuccessful, extinguishing any consideration towards a viable therapeutic strategy7. Here we show that tri-complex inhibitors, that is, molecular glues with the ability to recruit cyclophilin A (CYPA) to the active state of RAS have a dual mechanism of action: not only do they prevent activated RAS from binding to its effectors, but, unexpectedly, they also stimulate GTP hydrolysis. Drug-bound CYPA complexes modulate residues in the switch II motif of RAS to coordinate the nucleophilic attack on the ɣ phosphate of GTP, in a mutation-specific manner. RAS mutants most sensitive to stimulation of GTPase activity were more susceptible to treatment compared to mutants whose hydrolysis could not be enhanced, suggesting that pharmacologic stimulation of hydrolysis potentiates the therapeutic effects of tri-complex inhibitors for specific RAS mutants. This study lays the foundation for developing a new class of therapeutics that inhibit cancer growth by stimulating mutant GTPase activity.

CK and LRRK2 Involvement in Neurodegenerative Diseases.

Neurodegenerative diseases (NDDs) are currently the most widespread neuronal pathologies in the world. Among these, the most widespread are Alzheimer's disease (AD), dementia, Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD)-all characterized by a progressive loss of neurons in specific regions of the brain leading to varied clinical symptoms. At the basis of neurodegenerative diseases, an emerging role is played by genetic mutations in the leucine-rich repeat kinase 2 (LRRK2) gene that cause increased LRRK2 activity with consequent alteration of neuronal autophagy pathways. LRRK2 kinase activity requires GTPase activity which functions independently of kinase activity and is required for neurotoxicity and to potentiate neuronal death. Important in the neurodegeneration process is the upregulation of casein kinase (CK), which causes the alteration of the AMPK pathway by enhancing the phosphorylation of α-synuclein and huntingtin proteins, known to be involved in PD and HD, and increasing the accumulation of the amyloid-β protein (Aβ) for AD. Recent research has identified CK of the kinases upstream of LRRK2 as a regulator of the stability of the LRRK2 protein. Based on this evidence, this review aims to understand the direct involvement of individual kinases in NDDs and how their crosstalk may impact the pathogenesis and early onset of neurodegenerative diseases.

CAMP/PKA-mediated in vitro angiogenesis: A novel interplay between PKA, RhoA/ROCK, and VEGFR2 signalling

Abstract Background and Aims Others and we have previously demonstrated that cAMP/PKA signalling stabilise endothelial cell (EC) barrier function via modulating the activities of Rho GTPases, mainly RhoA and Rac1. In the present study we analysed whether cAMP/PKA also modulates EC angiogenesis capacity and whether Rho GTPases are involved in this function. Methods The study was carried out on cultured human umbilical vein ECs (HUVECs). RhoA and Rac1 activities were genetically manipulated by lentiviral-mediated over expression of dominant negative (DN) and constitutive active (CA) forms of RhoA and Rac1. Pharmacologically, specific activation and inhibition of PKA was achieved by using cAMP analogue N6-Benzoyl-cAMP (5 mM) and PKI (1 µM), respectively. Pharmacologically, Rac1 was inhibited using NSC 23766 (10 µM) and RhoA was activated using Rho activator I (Cytoskeleton Inc.). In vitro angiogenesis was analysed by 3-D spheroid assay and matrigel tube formation assay. Results Pharmacologically, specific activation of PKA induced EC migration (Wound healing assay), tube formation, and 3-D spheroids and potentiated the VEGF-induced in vitro angiogenesis. These pro-angiogenesis activities were abrogated by highly specific cell-permeable peptide inhibitor (PKI) of PKA. Activation of cAMP/PKA-signalling resulted in an increased VEGFR2 and Akt phosphorylation, increased Rac1 activity, and a strong inhibition of RhoA/Rock pathway. Pharmacological activation of RhoA but not inhibition of Rac1 abrogated PKA-induced VEGFR2 phosphorylation, tube formation and 3-D spheroids. Lentiviral mediated over-expression of constitutive active form of RhoA but not Rac1 abrogated PKA-induced VEGFR2 and Akt phosphorylation and angiogenesis. Moreover, pharmacological inhibition of Akt also abrogated PKA-mediated VEGFR2 phosphorylation and angiogenesis. Likewise, over expression of either dominant negative RhoA or pharmacological inhibitors of Rho kinase (ROCK) promoted basal and potentiated PKA-mediated VEGFR2 and Akt phosphorylation and angiogenesis. Conclusion We describe for the first time a novel interplay between PKA, RhoA/ROCK, Akt, and VEGFR2 signalling and angiogenesis. Inhibition of RhoA/ROCK plays an important role in mediating PKA-induced angiogenesis and activation of RhoA/ROCK signalling may offer an important target to intervene therapeutic angiogenesis.

RAB4A is a master regulator of cancer cell stemness upstream of NUMB–NOTCH signaling

Cancer stem cells (CSCs) are a group of specially programmed tumor cells that possess the characteristics of perpetual cell renewal, increased invasiveness, and often, drug resistance. Hence, eliminating CSCs is a major challenge for cancer treatment. Understanding the cellular programs that maintain CSCs, and identifying the critical regulators for such programs, are major undertakings in both basic and translational cancer research. Recently, we have reported that RAB4A is a major regulator of epithelial-to-mesenchymal transition (EMT) and it does so mainly through regulating the activation of RAC1 GTPase. In the current study, we have delineated a new signaling circuitry through which RAB4A transmits its control of cancer stemness. Using in vitro and in vivo studies, we show that RAB4A, as the upstream regulator, relays signal stepwise to NUMB, NOTCH1, RAC1, and then SOX2 to control the self-renewal property of multiple cancer cells of diverse tissue origins. Knockdown of NUMB, or overexpression of NICD (the active fragment NOTCH1) or SOX2, rescued the in vitro sphere-forming and in vivo tumor-forming abilities that were lost upon RAB4A knockdown. Furthermore, we discovered that the chain of control is mostly through transcriptional regulation at every step of the pathway. The discovery of the novel signaling axis of RAB4A–NUMB–NOTCH–SOX2 opens the path for further expansion of the signaling chain and for the identification of new regulators and interacting proteins important for CSC functions, which can be explored to develop new and effective therapies.

Abl kinases regulate FGF signaling independent of Crk phosphorylation to prevent Peters anomaly.

Peters anomaly, the most common cause of congenital corneal opacity, stems from corneal-lenticular adhesion. Despite numerous identified mutations, a cohesive molecular framework of the disease's etiology remains elusive. Here, we identified Abl kinases as pivotal regulators of FGF signaling, as genetic ablation of Abl kinases restores lens induction even in the absence of FGF signaling. Intriguingly, both Abl kinase deficiency and increased FGF-Ras activity result in Peters anomaly independent of ERK signaling, which can be rescued by allelic deletion of Abl substrate, Crk. However, contrary to the prevailing belief that Abl kinases regulate Crk proteins by direct phosphorylation, mutations at Abl kinase phosphorylation sites on Crk and CrkL did not yield any observable effects. Instead, our findings reveal that Abl kinases phosphorylate Ptpn12, which in turn inhibits p130Cas phosphorylation and Crk recruitment, crucial for Rho GTPases activation and cytoskeletal dynamics. Consequently, Abl kinase deficiency reduces actomyosin contractility within the lens vesicle and genetically interacts with RhoA inhibition. Conversely, Rac1 deletion mitigates Peters anomaly in models with aberrant FGF, Abl kinase and RhoA signaling. Our results demonstrate that Abl kinases regulate FGF signaling to balance RhoA and Rac1 activity via the Ptpn12-p130Cas pathway, suggesting that targeting tension-mediated lens vesicle separation could be a therapeutic strategy for Peters anomaly.

A homozygous variant in ARHGAP39 is associated with lethal cerebellar vermis hypoplasia in a consanguineous Saudi family

Cerebellar vermis hypoplasia refers to a varying degree of incomplete development of the cerebellum and vermis. A Saudi family with four affected individuals with cerebellar vermis hypoplasia, facial dysmorphology, visual impairment, skeletal, and cardiac abnormalities was ascertained in this study. Three out of four patients could not survive longer and had died in early infancy. Genetic analysis of the youngest affected was performed by genome-wide homozygosity mapping coupled with whole exome sequencing (WES), followed by Sanger validation. Genome-wide genotyping analysis mapped the phenotype to chromosome 8q24.3. Using an autosomal recessive model, considering deleterious variants with minor allele frequency of less than 0.001 in WES data, a homozygous missense variant (NM_025251.2; ARHGAP39; c.1301G > T; p.Cys434Phe) was selected as a potential candidate for the phenotype. The variant (c.1301G > T) in the ARHGAP39 is in the region of homozygosity on chromosome 8q24.3. ARHGAP39 is a Rho GTPase-activating protein 39 and has been known to regulate apoptosis, cell migration, neurogenesis, and cerebral and hippocampal dendritic spine morphology. Mice homozygous for arhgap39 knockouts have shown premature embryonic lethality. Our findings present the first ever human phenotype associated with ARHGAP39 alteration.

Comprehensive proteomic analysis of buffalo milk extracellular vesicles

Extracellular vesicles are secretory vesicles involved in cell-to-cell communication via their encapsulated cargo of proteins, lipids, and nucleic acids. Bovine milk provides a rich source of extracellular vesicles (mEVs) that have been studied as therapeutics and drug delivery systems. Therefore, insight into the mEV cargo, such as its proteome, may help in understanding the molecular mechanism underlying the potential health benefits attributed to the mEVs. Hence, mEVs were isolated from healthy buffalo milk after screening the milk somatic cell count. The total proteins of mEVs were analyzed using LC-MS, and 331 proteins were found commonly present among three buffalo milk samples. These proteins were primarily derived from extracellular regions and lysosomes. The major biological roles associated with the proteins were immune response, metabolism, and cell cycle regulation. The molecular functions of the proteins were transporter activity, catalytic activity, and GTPase activity. Further, comparative analysis with the previously available bovine mEVs proteome data showed 114 proteins to be newly identified in the buffalo mEVs. The biological pathways associated with these proteins may play a major role in muscle development. These findings shed a light on the potential health benefits of buffalo mEVs as therapeutics as well as drug delivery vehicles.

EPHB4-RASA1 Inhibition of PIEZO1 Ras Activation Drives Lymphatic Valvulogenesis.

EPHB4 (ephrin receptor B4) and the RASA1 (p120 Ras GTPase-activating protein) are necessary for the development of lymphatic vessel (LV) valves. However, precisely how EPHB4 and RASA1 regulate LV valve development is unknown. In this study, we examine the mechanisms by which EPHB4 and RASA1 regulate the development of LV valves. We used LV-specific inducible EPHB4-deficient mice and EPHB4 knockin mice that express a form of EPHB4 that is unable to bind RASA1 yet retains protein tyrosine kinase activity (EPHB4 2YP) to study the role of EPHB4 and RASA1 in LV valve development in the embryo and LV valve maintenance in adults. We also used human dermal lymphatic endothelial cells in vitro to study the role of EPHB4 and RASA1 as regulators of LV valve specification induced by oscillatory shear stress, considered the trigger for LV valve specification in vivo. LV valve specification, continued valve development postspecification, and LV valve maintenance were blocked upon induced loss of EPHB4 in LV. LV specification and maintenance were also impaired in EPHB4 2YP mice. Defects in LV development were reversed by inhibition of the Ras-MAPK (mitogen-activated protein kinase) signaling pathway. In human dermal lymphatic endothelial cells, loss of expression of EPHB4 or its ephrin b2 ligand, loss of expression of RASA1, and inhibition of physical interaction between EPHB4 and RASA1 resulted in dysregulated oscillatory shear stress-induced Ras-MAPK activation and impaired expression of LV specification markers that could be rescued by Ras-MAPK pathway inhibition. The same results were observed when human dermal lymphatic endothelial cells were stimulated with the Yoda1 agonist of the PIEZO1 oscillatory shear stress sensor. Although Yoda1 increased the number of LV valves when administered to wild-type embryos, it did not increase LV valve number when administered to EPHB4 2YP embryos. EPHB4 is necessary for LV valve specification, continued valve development postspecification, and valve maintenance. LV valve specification requires physical interaction between EPHB4 and RASA1 to limit activation of the Ras-MAPK pathway in lymphatic endothelial cells. Specifically, EPHB4-RASA1 physical interaction is necessary to dampen Ras-MAPK activation induced through the PIEZO1 oscillatory shear stress sensor. These findings reveal the mechanism by which EPHB4 and RASA1 regulate the development of LV valves.