Guanine Nucleotide Exchange Factor Research Articles

Determining the Electrostatic Contributions of GTPase-GEF Complexes on Interfacial Drug Binding Specificity: A Case Study of a Protein-Drug-Protein Complex.

Understanding the factors that contribute to specificity of protein-protein interactions allows for design of orthosteric small molecules. Within this environment, a small molecule requires both structural and electrostatic complementarity. While the structural contribution to protein-drug-protein specificity is well characterized, electrostatic contributions require more study. To this end, we used a series of protein complexes involving Arf1 bound to guanine nucleotide exchange factors (GEFs) that are sensitive or resistant to the small molecule brefeldin A (BFA). By comparing BFA-sensitive Arf1-Gea1p and Arf1-ARNO with different combinations of four BFA sensitizing ARNO mutations (ARNOwt, ARNO1M, ARNO3M, and ARNO4M), we describe how electrostatic environments at each interface guide BFA binding specificity. We labeled Arf1 with cyanocysteine at several interfacial sites and measured by nitrile adsorption frequencies to map changes in electric field at each interface using the linear Stark equation. Temperature dependence of nitrile vibrational spectra was used to investigate differences in hydrogen bonding environments. These comparisons showed that interfacial electric field at the surface of Arf1 varied substantially depending on the GEF. The greatest differences were seen between Arf1-ARNOwt and Arf1-ARNO4M, suggesting a greater change in electric field is required for BFA binding to Arf1-ARNO. Additionally, rigidity of the interface of the Arf1-ARNO complex correlated strongly with BFA sensitivity, indicating that flexible interfaces are sensitive to disruption upon orthosteric small molecule binding. These findings demonstrate a qualitatively consistent electrostatic environment for Arf1 binding and more subtle differences preventing BFA specificity. We discuss how these results will guide improved design of other small molecules that can target protein-protein interfaces.

Spatiotemporal recruitment of the ubiquitin-specific protease USP8 directs endosome maturation.

The spatiotemporal transition of small GTPase Rab5 to Rab7 is crucial for early-to-late endosome maturation, yet the precise mechanism governing Rab5-to-Rab7 switching remains elusive. USP8, a ubiquitin-specific protease, plays a prominent role in the endosomal sorting of a wide range of transmembrane receptors and is a promising target in cancer therapy. Here, we identified that USP8 is recruited to Rab5-positive carriers by Rabex5, a guanine nucleotide exchange factor (GEF) for Rab5. The recruitment of USP8 dissociates Rabex5 from early endosomes (EEs) and meanwhile promotes the recruitment of the Rab7 GEF SAND-1/Mon1. In USP8-deficient cells, the level of active Rab5 is increased, while the Rab7 signal is decreased. As a result, enlarged EEs with abundant intraluminal vesicles accumulate and digestive lysosomes are rudimentary. Together, our results reveal an important and unexpected role of a deubiquitinating enzyme in endosome maturation.

Natural variation in GhROPGEF5 contributes to longer and stronger cotton fibers.

Length and strength are key parameters impacting the quality of textiles that can be produced from cotton fibers, and therefore are important considerations in cotton breeding. Through map-based cloning and function analysis, we demonstrated that GhROPGEF5, encoding a ROP guanine nucleotide exchange factor, was the gene controlling fiber length and strength at qFSA10.1. Evolutionary analysis revealed that a base deletion in the third exon of GhROPGEF5 resulting in superior fiber length and strength was a rare mutation occurring in a tiny percentage of Upland cottons, with reduced fiber yield hindering its spread. GhROPGEF5 interacted with and activated GhROP10. Knockout or mutation of GhROPGEF5 resulted a loss of the ability to activate GhROP10. Knockout of GhROPGEF5 or GhROP10 affected the expression of many downstream genes associated with fiber elongation and secondary wall deposition, prolonged fiber elongation and delayed secondary wall deposition, producing denser fiber helices and increasing fiber length and strength. These results revealed new molecular aspects of fiber development and revealed a rare favorable allele for improving fiber quality in cotton breeding.

CalDAG-GEFI acts as a guanine nucleotide exchange factor for LRRK2 to regulate LRRK2 function and neurodegeneration.

Mutations in LRRK2 are the most common genetic cause of Parkinson's disease (PD). LRRK2 protein contains two enzymatic domains: a GTPase (Roc-COR) and a kinase domain. Disease-causing mutations are found in both domains. Now, studies have focused largely on LRRK2 kinase activity, while attention to its GTPase function is limited. LRRK2 is a guanine nucleotide-binding protein, but the mechanism of direct regulation of its GTPase activity remains unclear and its physiological GEF is not known. Here, we identified CalDAG-GEFI (CDGI) as a physiological GEF for LRRK2. CDGI interacts with LRRK2 and increases its GDP to GTP exchange activity. CDGI modulates LRRK2 cellular functions and LRRK2-induced neurodegeneration in both LRRK2 Drosophila and mouse models. Together, this study identified the physiological GEF for LRRK2 and provides strong evidence that LRRK2 GTPase is regulated by GAPs and GEFs. The LRRK2 GTPase, GAP, or GEF activities have the potential to serve as therapeutic targets, which is distinct from the direct LRRK2 kinase inhibition.

LncRNA H19 Activates the RAS-MAPK Signaling Pathway via miR-140-5p/SOS1 Axis in Malignant Liver Tumors.

To study the influences of LncRNA H19 (H19) on malignant liver tumor cells and elucidate the underlying molecular mechanisms. H19 expression in liver tumor tissues, matched normal liver tissues, human liver malignant tumor cell lines and the human hepatocyte line LO2 was assessed via quantitative RT-PCR. Cell viability analysis and Matrigel invasion analysis were performed to evaluate the effects of H19 on cell proliferation and invasion. Luciferase reporter analysis was carried out to assess the interaction between miR-140-5p and SOS Ras/Rac guanine nucleotide exchange factor 1 (SOS1). The influence of H19 on the Ras-MAPK signalling pathway was evaluated by detecting key protein levels via active Ras pull-down analysis and Western blot analysis. H19 expression was lower in liver cancer samples than in matched normal liver tissue samples. H19 overexpression enhanced the proliferation and invasion of HepG2 and SMMC-7721 cells. H19 overexpression increased the level of activated Ras. The expression levels of phosphorylated Raf, phosphorylated ERK and phosphorylated MEK were increased by H19 overexpression. H19 knockdown had the opposite effect. Treatment with a MAPK inhibitor significantly reversed the influence of H19 overexpression on liver malignant tumor cell growth and invasion. The MAPK activator reversed the opposing effects of H19 silencing. H19 overexpression increased the protein level of SOS1, and miR-140-5p directly targeted SOS1. H19 can activate the Ras-MAPK signalling pathway via the miR-140-5p/SOS1 axis in malignant liver tumour cells.

GIV/Girdin Modulation of Microglial Activation in Ischemic Stroke: Impact of FTO-Mediated m6A Modification.

Ischemic stroke (IS) is one of the most common causes of death in the world. The lack of effective pharmacological treatments for IS was primarily due to a lack of understanding of its pathogenesis. Gα-Interacting vesicle-associated protein (GIV/Girdin) is a multi-modular signal transducer and guanine nucleotide exchange factor that controls important signaling downstream of multiple receptors. The purpose of this study was to investigate the role of GIV in IS. In the present study, we found that GIV is highly expressed in the central nervous system (CNS). GIV protein level was decreased, while GIV transcript level was increased in the middle cerebral artery occlusion reperfusion (MCAO/R) mice model. Additionally, GIV was insensitive lipopolysaccharide (LPS) exposure. Interestingly, we found that GIV overexpression dramatically restrained microglial activation, inflammatory response, and M1 polarization in BV-2 microglia induced by oxygen-glucose deprivation and reoxygenation (OGD/R). On the contrary, GIV knockdown had the opposite impact. Mechanistically, we found that GIV activated the Wnt/β-catenin signaling pathway by interacting with DVL2 (disheveled segment polarity protein 2). Notably, m6A demethylase fat mass and obesity-associated protein (FTO) decreased the N6-methyladenosine (m6A) modification-mediated increase of GIV expression and attenuated the inflammatory response in BV-2 stimulated by OGD/R. Taken together, our results demonstrate that GIV inhibited the inflammatory response via activating the Wnt/β-catenin signaling pathway which expression regulated in an FTO-mediated m6A modification in IS. These results broaden our understanding of the role of the FTO-GIV axis in IS development.

ARHGAP29 promotes keratinocyte proliferation and migration in vitro and is dispensable for in vivo wound healing.

RhoA GTPases play critical roles in actin cytoskeletal remodeling required for controlling a diverse range of cellular functions including cell proliferation, adhesion, migration and changes in cell shape, all required for cutaneous wound healing. RhoA cycles between an active GTP-bound and an inactive GDP-bound form, a process regulated by guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs). ARHGAP29 is a GAP expressed in skin keratinocytes and is decreased in the absence of interferon regulator factor 6, a critical regulator of cell proliferation, migration, and wound healing. However, the role for ARHGAP29 in keratinocyte biology is unknown. We generated ARHGAP29 knockdown keratinocyte cell lines and show they displayed increased filamentous actin, phospho-myosin regulatory light chain, cell area and population doubling time. Furthermore, we found that ARHGAP29 knockdown keratinocytes displayed significant delays in scratch wound closure in both single and collective cell migration conditions; these delays were rescued by both adding back ARHGAP29 or adding a ROCK inhibitor to ARHGAP29 knockdown cells. In vivo, however, Arhgap29 heterozygotes or keratinocyte-specific knockouts showed on-time wound healing. These data demonstrate that ARHGAP29 is required for keratinocyte morphology, proliferation and migration in vitro but is dispensable during wound healing in vivo.

Disruption of Iqsec1 in mice leads to embryonic lethality with reduced large apical vacuoles in the visceral endoderm.

Iqsec1 (IQ motif and Sec7 domain-containing protein 1), also known as BRAG2 (Brefeldin A-resistant Arf-GEF 2), is a guanine nucleotide exchange factor that regulates membrane trafficking, cytoskeletal organization, and signal transduction by activating class II and III ADP-ribosylation factors. To investigate the physiological role of Iqsec1 at the whole animal level, we generated Iqsec1-deficient mice using CRISPR/Cas9-mediated gene editing. Nearly all Iqsec1-/- mice (99%) exhibited embryonic lethality with severe growth retardation. Electron microscopy revealed that Iqsec1-/- embryos at embryonic day 8.5 lacked large apical vacuoles in visceral endoderm cells of the yolk sac, compared with controls. These findings suggest that Iqsec1 plays a critical role in embryogenesis, likely through regulation of membrane trafficking in visceral endoderm cells.

RNAseq and targeted metabolomics implicate RIC8 in regulation of energy homeostasis, amino acid compartmentation, and asexual development in Neurospora crassa

ABSTRACT Heterotrimeric G protein signaling pathways control growth and development in eukaryotes. In the multicellular fungus Neurospora crassa , the guanine nucleotide exchange factor RIC8 regulates heterotrimeric Gα subunits. In this study, we used RNAseq and liquid chromatography-mass spectrometry (LC-MS) to profile the transcriptomes and metabolomes of N. crassa wild type, the Gα subunit mutants Δ gna-1 and Δ gna-3 , and Δ ric8 strains. These strains exhibit defects in growth and asexual development (conidiation), with wild-type and Δ gna-1 mutants producing hyphae in submerged cultures, while Δ gna-3 and Δ ric8 mutants develop conidiophores, particularly in the Δ ric8 mutant. RNAseq analysis showed that the Δ gna-1 mutant possesses 159 mis-regulated genes, while Δ gna-3 and Δ ric8 strains have more than 1,000 each. Many of the mis-regulated genes are involved in energy homeostasis, conidiation, or metabolism. LC-MS revealed changes in levels of primary metabolites in the mutants, with several arginine metabolic intermediates impacted in Δ ric8 strains. The differences in metabolite levels could not be fully explained by the expression or activity of pathway enzymes. However, transcript levels for two predicted vacuolar arginine transporters were affected in Δ ric8 mutants. Analysis of arginine and ornithine levels in transporter mutants yielded support for altered compartmentation of arginine and ornithine between the cytosol and vacuole in Δ ric8 strains. Furthermore, we validated previous reports that arginine and ornithine levels are low in wild-type conidia. Our results suggest that RIC8 regulates asexual sporulation in N. crassa at least in part through altered expression of vacuolar transporter genes and the resultant mis-compartmentation of arginine and ornithine. IMPORTANCE Resistance to inhibitors of cholinesterase-8 (RIC8) is an important regulator of heterotrimeric Gα proteins in eukaryotes. In the filamentous fungus Neurospora crassa , mutants lacking ric8 undergo inappropriate asexual development (macroconidiation) during submerged growth. Our work identifies a role for RIC8 in regulating expression of transporter genes that retain arginine and ornithine in the vacuole (equivalent of the animal lysosome) and relates this function to the developmental defect. Arginine is a critical cellular metabolite, both as an amino acid for protein synthesis and as a precursor for an array of compounds, including proline, ornithine, citrulline, polyamines, creatine phosphate, and nitric oxide. These results have broad relevance to human physiology and disease, as arginine modulates immune, vascular, hormonal, and other functions in humans.

Bcl2l12, a novel protein interacting with Arf6, triggers Schwann cell differentiation program.

Schwann cells are glial cells in the peripheral nervous system (PNS); they wrap neuronal axons with their differentiated plasma membranes called myelin sheaths. Although the physiological functions, such as generating saltatory conduction, have been well studied in the PNS, the molecular mechanisms by which Schwann cells undergo their differentiation program without apparent morphological changes before dynamic myelin sheath formation remain unclear. Here, for the first time, we report that Arf6, a small GTP/GDP-binding protein controlling morphological differentiation, and the guanine-nucleotide exchange factors cytohesin proteins are involved in the regulation of Schwann cell differentiation marker expression in primary Schwann cells. Specific inhibition of Arf6 and cytohesins by NAV-2729 and SecinH3, respectively, decreased expression of marker proteins 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) and glial fibrillary acidic protein (GFAP). Similar results using promoter assays were observed using the IMS32 Schwann cell line. Furthermore, using an affinity-precipitation technique, we identified Bcl2-like 12 (Bcl2l12) as a novel GTP-bound Arf6-interacting protein. Knockdown of Bcl2l12 using a specific artificial miRNA decreased expression of marker proteins. The knockdown also led to decreased filamentous actin extents. These results suggest that Arf6 and Bcl2l12 can trigger Schwann cell differentiation, providing evidence for a molecular relay that underlies how Schwann cells differentiate.

Dissecting genomic regions and underlying candidate genes in groundnut MAGIC population for drought tolerance

BackgroundGroundnut is mainly grown in the semi-arid tropic (SAT) regions worldwide, where abiotic stress like drought is persistent. However, a major research gap exists regarding exploring the genetic and genomic underpinnings of tolerance to drought. In this study, a multi-parent advanced generation inter-cross (MAGIC) population was developed and evaluated for five seasons at two locations for three consecutive years (2018–19, 2019–20 and 2020–21) under drought stress and normal environments.ResultsPhenotyping data of drought tolerance related traits, combined with the high-quality 10,556 polymorphic SNPs, were used to perform multi-locus model genome-wide association study (GWAS) analysis. We identified 37 significant marker-trait associations (MTAs) (Bonferroni-corrected) accounting, 0.91- 9.82% of the phenotypic variance. Intriguingly, 26 significant MTAs overlap on four chromosomes (Ah03, Ah07, Ah10 and Ah18) (harboring 70% of MTAs), indicating genomic hotspot regions governing drought tolerance traits. Furthermore, important candidate genes associated with leaf senescence (NAC transcription factor), flowering (B3 domain-containing transcription factor, Ulp1 protease family, and Ankyrin repeat-containing protein), involved in chlorophyll biosynthesis (FAR1 DNA-binding domain protein), stomatal regulation (Rop guanine nucleotide exchange factor; Galacturonosyltransferases), and associated with yield traits (Fasciclin-like arabinogalactan protein 11 and Fasciclin-like arabinogalactan protein 21) were found in the vicinity of significant MTAs genomic regions.ConclusionThe findings of our investigation have the potential to provide a basis for significant MTAs validation, gene discovery and development of functional markers, which could be employed in genomics-assisted breeding to develop climate-resilient groundnut varieties.

A novel role of AURKA kinase in erythroblast enucleation.

Generation of mammalian red blood cells requires the expulsion of polarized nuclei late in terminal erythroid differentiation. However, the mechanisms by which spherical erythroblasts determine the direction of nuclear polarization and maintain asymmetry during nuclear expulsion are poorly understood. Given the analogy of erythroblast enucleation to asymmetric cell division and the key role of Aurora kinases in mitosis, we sought to investigate the function of Aurora kinases in erythroblast enucleation. We found that AURKA (Aurora kinase A) is abundantly expressed in orthochromatic erythroblasts. Intriguingly, high-resolution confocal microscopy analyses revealed that AURKA co-localized with the centrosome on the side of the nucleus opposite its membrane contact point during polarization and subsequently translocated to the anterior end of the protrusive nucleus upon nuclear exit. Mechanistically, AURKA regulated centrosome maturation and localization via interaction with γ-tubulin to provide polarization orientation for the nucleus. Furthermore, we identified ECT2 (epithelial cell transforming 2), a guanine nucleotide exchange factor, as a new interacting protein and ubiquitination substrate of AURKA. After forming the nuclear protrusion, AURKA translocated to the anterior end of the protrusive nucleus to directly degrade ECT2, which is partly dependent on kinase activity of AURKA. Moreover, knockdown of ECT2 rescued impaired enucleation caused by AURKA inhibition. Our findings have uncovered a previously unrecognized role of Aurora kinases in the establishment of nuclear polarization and eventual nuclear extrusion and provide new mechanistic insights into erythroblast enucleation.

β-PIX-d, a Member of the ARHGEF7 Guanine Nucleotide Exchange Factor Family, Activates Rac1 and Induces Neuritogenesis in Primary Cortical Neurons.

β-PIX, a Rac1/Cdc42-specific guanine nucleotide exchange factor, is known to regulate actin cytoskeleton remodeling during cell migration. In this study, we investigated the effects of β-PIX-d, an isoform of β-PIX, on neocortical development and neuritogenesis. Overexpression of β-PIX-d in the embryonic neocortex induced increased cell clusters and enhanced neurite outgrowth in cortical neurons. Following in utero electroporation of β-PIX-d expression vectors into neuronal progenitor cells at embryonic day 13.5 (E13.5), histological analysis at postnatal day 0 (P0) revealed the presence of clustered neurons and neurites outside of the marginal zone (MZ). Immunofluorescence staining with the neuronal marker TuJ1 confirmed that the clustered structures were predominantly composed of neurons. Layer-specific marker analysis further demonstrated the misplacement of layer V-VI neurons into layer I and the subarachnoid space. In primary neocortical cultures, β-PIX-d overexpression promoted neuritogenesis and increased Rac1 activity, as detected by pull-down assays. These findings suggest that β-PIX-d and Rac1 interactions play a critical role in the formation of neocortical clustering and the regulation of neuritogenesis.

The CYK-4 GAP domain regulates cortical targeting of centralspindlin to promote contractile ring assembly and facilitate ring dissolution.

During cytokinesis, an equatorial contractile ring partitions the cell contents. Contractile ring assembly requires an equatorial zone of active GTP-bound RhoA generated by the guanine nucleotide exchange factor ECT21,2. ECT2 is activated by centralspindlin, a complex composed of two molecules each of kinesin-6 and CYK4. During anaphase, Centralspindlin is activated at the central spindle between the separating chromosomes and diffuses to the plasma membrane, where it engages with ECT2 via its N-terminal half3,4. The C-terminal half of CYK4 contains a lipid-binding C1 domain that contributes to plasma membrane targeting5 and a GTPase-activating protein (GAP) domain that has an interaction surface for a Rho family GTPase, whose functions have remained unclear 1,3,4,6,7. Here, using the one-cell stage C. elegans embryo as a model, we show that RhoA and the Rho-binding interface of the CYK4 GAP domain drive the recruitment of centralspindlin to the equatorial cortex. By contrast, a point mutant that selectively disrupts GAP activity does not prevent cortical centralspindlin recruitment but instead substantially delays dissipation of centralspindlin from the cortex. These findings suggest that positive feedback, in which centralspindlin recruitment promotes the generation of active RhoA and active RhoA drives centralspindlin recruitment, is central to the rapid assembly of the contractile ring within a narrow time window. They also indicate that the CYK4 GAP catalytic activity contributes to release of centralspindlin from the cortex, potentially to ensure timely dissolution of the contractile ring.

Dennd2c Negatively Controls Multinucleation and Differentiation in Osteoclasts by Regulating Actin Polymerization and Protrusion Formation.

Osteoclasts are bone-resorbing multinucleated giant cells formed by the fusion of monocyte/macrophage lineages. Various small GTPases are involved in the multinucleation and differentiation of osteoclasts. However, the roles of small GTPases regulatory molecules in osteoclast differentiation remain unclear. In the present study, we examined the role of Dennd2c, a putative guanine nucleotide exchange factor for Rab GTPases, in osteoclast differentiation. Knockdown of Dennd2c promoted osteoclast differentiation, resorption, and expression of osteoclast markers. Morphologically, Dennd2c knockdown induced the formation of larger osteoclasts with several protrusions. In contrast, overexpression of Dennd2c inhibited the multinucleation and differentiation of osteoclasts, bone resorption, and the expression of osteoclast markers. Dennd2c-overexpressing macrophages exhibited spindle-shaped mononuclear cells and long thin protrusions. Treatment of Dennd2c-overexpressing cells with the Cdc42 inhibitor ML-141 or the Rac1 inhibitor 6-thio-GTP prevented protrusion formation. Moreover, treatment of Dennd2c-overexpressing cells with the actin polymerization inhibitor latrunculin B restored multinucleated and TRAP-positive osteoclast formation. These results indicate that Dennd2c negatively regulates osteoclast differentiation and multinucleation by modulating protrusion formation in macrophages.

Targeted Degradation of SOS1 Exhibits Potent Anticancer Activity and Overcomes Resistance in KRAS-Mutant Tumors and BCR-ABL-Positive Leukemia.

SOS1 is an essential guanine nucleotide exchange factor for RAS that also plays a critical role in the activation of the small GTPase RAC mediated by BCR-ABL in leukemogenesis. Despite this, small molecule inhibitors targeting SOS1 have shown limited efficacy in clinical trials for KRAS mutant cancers, and their potential as a therapeutic approach for chronic myeloid leukemia (CML) remains largely unexplored. In this study, we developed a potent SOS1 PROTAC SIAIS562055, which was designed by connecting a CRBN ligand to an analogue of the SOS1 inhibitor BI-3406. SIAIS562055 exhibited sustained degradation of SOS1 and inhibition of downstream ERK pathways, resulting in superior anti-proliferative activity compared to small molecule inhibitors. SIAIS562055 also potentiated the activity of both KRAS inhibitors in KRAS-mutant cancers and ABL inhibitors in BCR-ABL+ CML. In KRAS-mutant xenografts, SIAIS562055 displayed promising antitumor potency as a monotherapy and enhanced ERK inhibition and tumor regression when combined with KRAS inhibitors, overcoming acquired resistance. In CML cells, SIAIS562055 promoted the active uptake of BCR-ABL inhibitors by upregulating the carnitine/organic cation transporter SLC22A4. SIAIS562055 and BCR-ABL inhibitors synergistically enhanced inhibition of ABL phosphorylation and downstream signaling, demonstrating robust antitumor activities in both mouse xenografts and primary CML patient samples. In summary, this study suggests that PROTAC-mediated SOS1 degradation represents an effective therapeutic strategy for treating not only KRAS-mutant cancers but also BCR-ABL-harboring leukemia.

Guanine nucleotide exchange factors and colon neoplasia.

Despite many diagnostic and therapeutic advances, colorectal cancer (CRC) remains the second leading cause of cancer death for men and women in the United States. Alarmingly, for reasons currently unknown, the demographics of this disease have shifted towards a younger population. Hence, understanding the molecular mechanisms underlying CRC initiation and progression and leveraging these findings for therapeutic purposes remains a priority. Here, we review critically the evidence that canonical and noncanonical actions of guanine nucleotide exchange factors (GEFs) play important roles in CRC evolution. Rho GEF GTPases, which switch between inactive GDP-bound and active GTP-bound states, are commonly overexpressed and activated in a variety of cancers, including CRC, and may be tractable therapeutic targets. In addition to comprehensively reviewing this field, we focus on Rho/Rac GEFs that are involved in regulating key functions of normal and neoplastic cells like cell polarity, vesicle trafficking, cell cycle regulation, and transcriptional dynamics. Prime examples of such Rho/Rac GEFs include βPak-interacting exchange factor (βPix), a Rho family GEF for Cdc42/Rac1, Tiam1, GEF-H1, RGNEF, and other GEFs implicated in CRC development and progression. Throughout this analysis, we explore how these findings fill key gaps in knowledge regarding the molecular basis of colon carcinogenesis and how they may be leveraged to treat advanced CRC. Lastly, we address potential future directions for research into the role of GEFs as CRC biomarkers and therapeutic targets. In this regard, leveraging the noncanonical actions of GEFs appears to provide a relatively unexplored opportunity requiring further investigation.

Phenotype and Genotype of Children with ALS2 gene-Related Disorder.

The Alsin Rho Guanine Nucleotide Exchange Factor (ALS2) gene encodes a protein alsin that functions as a guanine nucleotide exchange factor. The variations in ALS2 gene leads to degeneration of upper motor neurons of the corticospinal tract. The phenotypes resulting from variants in ALS2 gene are infantile-onset ascending hereditary spastic paralysis (IAHSP, OMIM # 607225), juvenile primary lateral sclerosis (JPLS, OMIM # 606353), and juvenile amyotrophic lateral sclerosis (JALS, OMIM # 205100). Our study objectives were to describe the clinical phenotype and genotype of children with an established diagnosis of ALS2 gene-related disorder. The clinical details, laboratory data, and genotype findings of children with an established diagnosis of ALS2 gene-related disorder were collected from the hospital electronic database after obtaining institutional review board approval. One family with three affected siblings, a second family with a proband and an affected fetus, and a third family with two affected siblings with ALS2 gene variants were identified. IAHSP was diagnosed in all of our patients with variants in ALS2 gene. The clinical findings observed in our patients were insidious onset progressive spastic paraparesis, contractures, and dysarthria. Nonsense variants were observed in four patients while frameshift variant was observed in one family. Novel variants in ALS2 gene were identified in two unrelated families. ALS2 mutation results in rare neurodegenerative disorders with the clinical spectrum encompassing IAHSP, JPLS, and JALS disorders. In view of allelic heterogeneity described in the literature, more research studies are needed for establishing genotype-phenotype correlation in patients with ALS2 gene-related disorder.

Roles of the Dbl family of RhoGEFs in mechanotransduction - a review.

Rho guanine nucleotide exchange factors (RhoGEFs) comprise a wide range of proteins with a common domain responsible for the activation of the Rho family of small GTPases and various domains in other regions. The evolutionary divergence of RhoGEFs enables actin cytoskeletal reorganization, leading to complex cellular responses in higher organisms. In this review, we address the involvement of RhoGEFs in the mechanical stress response of mammalian cells. The cellular mechanical stress response is essential for the proper and orderly regulation of cell populations, including the maintenance of homeostasis, tissue morphogenesis, and adaptation to the mechanical environment. In particular, this review focuses on the recent findings regarding the Dbl family of RhoGEFs involved in mechanical stress responses at the cell-cell and cell-substrate adhesion sites, and their molecular mechanisms underlying actin cytoskeleton remodeling and signal transduction.

RABIF promotes hepatocellular carcinoma progression through regulation of mitophagy and glycolysis

The RAB interacting factor (RABIF) is a putative guanine nucleotide exchange factor that also functions as a RAB-stabilizing holdase chaperone. It has been implicated in pathogenesis of several cancers. However, the functional role and molecular mechanism of RABIF in hepatocellular carcinoma (HCC) are not entirely known. Here, we demonstrate an upregulation of RABIF in patients with HCC, correlating with a poor prognosis. RABIF inhibition results in decreased HCC cell growth both in vitro and in vivo. Our study reveals that depleting RABIF attenuates the STOML2-PARL-PGAM5 axis-mediated mitophagy. Consequently, this reduction in mitophagy results in diminished mitochondrial reactive oxygen species (mitoROS) production, thereby alleviating the HIF1α-mediated downregulation of glycolytic genes HK1, HKDC1, and LDHB. Additionally, we illustrate that RABIF regulates glucose uptake by controlling RAB10 expression. Importantly, the knockout of RABIF or blockade of mitophagy sensitizes HCC cells to sorafenib. This study uncovers a previously unrecognized role of RABIF crucial for HCC growth and identifies it as a potential therapeutic target.