NLRP4E regulates actin cap formation through SRC and CDC42 during oocyte meiosis.

BACKGROUND: Members of the nucleotide-binding oligomerization domain, leucine rich repeat and pyrin domain containing (NLRP) family regulate various physiological and pathological processes. However, none have been shown to regulate actin cap formation or spindle translocation during the asymmetric division of oocyte meiosis I. NLRP4E has been reported as a candidate protein in female fertility, but its function is unknown. METHODS: Immunofluorescence, reverse transcription polymerase chain reaction (RT-PCR), and western blotting were employed to examine the localization and expression levels of NLRP4E and related proteins in mouse oocytes. small interfering RNA (siRNA) and antibody transfection were used to knock down NLRP4E and other proteins. Immunoprecipitation (IP)-mass spectrometry was used to identify the potential proteins interacting with NLRP4E. Coimmunoprecipitation (Co-IP) was used to verify the protein interactions. Wild type (WT) or mutant NLRP4E messenger RNA (mRNA) was injected into oocytes for rescue experiments. In vitro phosphorylation was employed to examine the activation of steroid receptor coactivator (SRC) by NLRP4E. RESULTS: NLRP4E was more predominant within oocytes compared with other NLRP4 members. NLRP4E knockdown significantly inhibited actin cap formation and spindle translocation toward the cap region, resulting in the failure of polar body extrusion at the end of meiosis I. Mechanistically, GRIN1, and GANO1 activated NLRP4E by phosphorylation at Ser429 and Thr430; p-NLRP4E is translocated and is accumulated in the actin cap region during spindle translocation. Next, we found that p-NLRP4E directly phosphorylated SRC at Tyr418, while p-SRC negatively regulated p-CDC42-S71, an inactive form of CDC42 that promotes actin cap formation and spindle translocation in the GTP-bound form. CONCLUSIONS: NLRP4E activated by GRIN1 and GANO1 regulates actin cap formation and spindle translocation toward the cap region through upregulation of p-SRC-Tyr418 and downregulation of p-CDC42-S71 during meiosis I.

Estrogen inhibits TGF­ß1­stimulated cardiac fibroblast differentiation and collagen synthesis by promoting Cdc42.

17ß­estradiol (E2) can inhibit cardiac fibrosis in female patients with heart failure (HF) and activate cell division cycle 42 (Cdc42), however it is unknown whether 17ß­estradiol (E2) can ameliorate differentiation and collagen synthesis in TGF­ß1­stimulated mouse cardiac fibroblasts (MCFs) by regulating cell division cycle 42 (Cdc42). The present study aimed to investigate the roles of estrogen and Cdc42 in preventing myocardial fibrosis and the underlying molecular mechanisms. An ELISA was used to measure the levels of E2 and Cdc42 in the serum of patients with heart failure (HF), and western blotting was used to measure the expression levels of Cdc42 in TGF­ß1­stimulated immortalized MCFs. MCFs were transfected with a Cdc42 overexpression (OE) lentivirus or small interfering RNA (siRNA), or treated with a Cdc42 inhibitor (MLS­573151), and the function of Cdc42 was assessed by western blotting, immunofluorescence staining, reverse transcription­quantitative PCR and dual­luciferase reporter assays. Western blotting and immunofluorescence staining were performed to verify the protective effect of E2 on TGF­ß1­stimulated MCFs, and the association between the protective effect and Cdc42. The results demonstrated that Cdc42 levels were increased in the serum of patients with HF and were positively correlated with the levels of E2; however, Cdc42 levels were decreased in TGF­ß1­stimulated MCFs. Cdc42 inhibited MCF differentiation and collagen synthesis, as indicated by the protein expression of α­smooth muscle actin, collagen I and collagen III. Mechanistically, Cdc42 inhibited the transcription of TGF­ß1 by promoting the expression of p21 (RAC1)­activated kinase 1 (Pak1)/JNK/c­Jun signaling pathway proteins and inhibiting the activity of the Tgfb1 gene promoter. In addition, E2 inhibited the differentiation and collagen synthesis of TGF­ß1­stimulated MCFs, and promoted the protein expression of Pak1, JNK and c­Jun, consistent with the effects of Cdc42, whereas the effects of E2 were abolished when Cdc42 was knocked down. The aforementioned findings suggested that E2 could inhibit differentiation and collagen synthesis in TGF­ß1­stimulated MCFs by regulating Cdc42 and the downstream Pak1/JNK/c­Jun signaling pathway.

Cardiomyocytes, cardiac endothelial cells and fibroblasts contribute to anthracycline-induced cardiac injury through RAS-homologous small GTPases RAC1 and CDC42.

The clinical use of the DNA damaging anticancer drug doxorubicin (DOX) is limited by irreversible cardiotoxicity, which depends on the cumulative dose. The RAS-homologous (RHO) small GTPase RAC1 contributes to DOX-induced DNA damage formation and cardiotoxicity. However, the pathophysiological relevance of other RHO GTPases than RAC1 and different cardiac cell types (i.e., cardiomyocytes, non-cardiomyocytes) for DOX-triggered cardiac damage is unclear. Employing diverse in vitro and in vivo models, we comparatively investigated the level of DOX-induced DNA damage in cardiomyocytes versus non-cardiomyocytes (endothelial cells and fibroblasts), in the presence or absence of selected RHO GTPase inhibitors. Non-cardiomyocytes exhibited the highest number of DOX-induced DNA double-strand breaks (DSB), which were efficiently repaired in vitro. By contrast, rather low levels of DSB were formed in cardiomyocytes, which however remained largely unrepaired. Moreover, DOX-induced apoptosis was detected only in non-cardiomyocytes but not in cardiomyocytes. Pharmacological inhibitors of RAC1 and CDC42 most efficiently attenuated DOX-induced DNA damage in all cell types examined in vitro. Consistently, immunohistochemical analyses revealed that the RAC1 inhibitor NSC23766 and the pan-RHO GTPase inhibitor lovastatin reduced the level of DOX-induced residual DNA damage in both cardiomyocytes and non-cardiomyocytes in vivo. Overall, we conclude that endothelial cells, fibroblasts and cardiomyocytes contribute to the pathophysiology of DOX-induced cardiotoxicity, with RAC1- and CDC42-regulated signaling pathways being especially relevant for DOX-stimulated DSB formation and DNA damage response (DDR) activation. Hence, we suggest dual targeting of RAC1/CDC42-dependent mechanisms in multiple cardiac cell types to mitigate DNA damage-dependent cardiac injury evoked by DOX-based anticancer therapy.

IQGAP1 and NWASP promote human cancer cell dissemination and metastasis by regulating ß1-integrin via FAK and MRTF/SRF.

Attachment of circulating tumor cells to the endothelial cells (ECs) lining blood vessels is a critical step in cancer metastatic colonization, which leads to metastatic outgrowth. Breast and prostate cancers are common malignancies in women and men, respectively. Here, we observe that ß1-integrin is required for human prostate and breast cancer cell adhesion to ECs under shear-stress conditions in vitro and to lung blood vessel ECs in vivo. We identify IQGAP1 and neural Wiskott-Aldrich syndrome protein (NWASP) as regulators of ß1-integrin transcription and protein expression in prostate and breast cancer cells. IQGAP1 and NWASP depletion in cancer cells decreases adhesion to ECs in vitro and retention in the lung vasculature and metastatic lung nodule formation in vivo. Mechanistically, NWASP and IQGAP1 act downstream of Cdc42 to increase ß1-integrin expression both via extracellular signal-regulated kinase (ERK)/focal adhesion kinase signaling at the protein level and by myocardin-related transcription factor/serum response factor (SRF) transcriptionally. Our results identify IQGAP1 and NWASP as potential therapeutic targets to reduce early metastatic dissemination.

Kisspeptin/KISS1R Signaling Modulates Human Airway Smooth Muscle Cell Migration.

Airway remodeling is a cardinal feature of asthma, associated with increased airway smooth muscle (ASM) cell mass and upregulation of extracellular matrix deposition. Exaggerated ASM cell migration contributes to excessive ASM mass. Previously, we demonstrated the alleviating role of Kp (kisspeptin) receptor (KISS1R) activation by Kp-10 in mitogen (PDGF [platelet-derived growth factor])-induced human ASM cell proliferation in vitro and airway remodeling in vivo in a mouse model of asthma. Here, we examined the mechanisms by which KISS1R activation regulates mitogen-induced ASM cell migration. KISS1R activation using Kp-10 significantly inhibited PDGF-induced ASM cell migration, further confirmed using KISS1R shRNA. Furthermore, KISS1R activation modulated F/G actin dynamics and the expression of promigration proteins like CDC42 (cell division control protein 42) and cofilin. Mechanistically, we observed reduced ASM RhoA-GTPAse with KISS1R activation. The antimigratory effect of KISS1R was abolished by PKA (protein kinase A)-inhibitory peptide. Conversely, KISS1R activation significantly increased cAMP and phosphorylation of CREB (cAMP-response element binding protein) in PDGF-exposed ASM cells. Overall, these results highlight the alleviating properties of Kp-10 in the context of airway remodeling.

Cell division cycle 42 attenuates high glucose-treated renal tubular epithelial cell apoptosis, fibrosis, and inflammation, but activates the PAK1/AKT pathway.

BACKGROUND: Cell division cycle 42 (CDC42) modulates metabolism, inflammation, and fibrosis to engage in the pathology of diabetic complications. This study intended to further investigate the influence of CDC42 on viability, apoptosis, inflammation, epithelial-mesenchymal transition, and fibrosis in high glucose (HG)-treated renal tubular epithelial cells. METHODS: HK-2 cells were exposed to HG medium (30 mM) to establish the diabetic nephropathy (DN) cellular model, then the cells were transfected with scramble overexpression control (oeNC) or CDC42 overexpression (oeCDC42) vectors. RESULTS: Both the level of CDC42 mRNA and protein were decreased in HG-treated HK-2 cells in a dose- and time-dependent manner. Then HG-treated HK-2 cells were proposed for the following experiments. It was found that CDC42 increased CCK-8 detected viability and EdU positive cells. On the contrary, CDC42 reduced cell apoptosis, which was reflected by decreased TUNEL positive rate, increased BCL2, and reduced BAX. Interestingly, CDC42 inhibited fibrosis, which was reflected by increased E-Cadherin, as well as decreased Vimentin, TGF-ß1, Collagen1, and α-SMA. Apart from these, CDC42 also attenuated proinflammatory cytokine production, including TNF-α, IL-1ß, and IL-6. Moreover, CDC42 activated the PAK1/AKT pathway, which was reflected by increased p-PAK1 and p-AKT. However, CDC42 did not affect p-ERK. CONCLUSION: CDC42 may retard DN progression via its regulation of renal tubular epithelial cell functions, which may be due to its stimulation of the PAK1/AKT pathway.

Myeloid Deletion of Cdc42 Protects Liver From Hepatic Ischemia-Reperfusion Injury via Inhibiting Macrophage-Mediated Inflammation in Mice.

BACKGROUND & AIMS: Hepatic ischemia-reperfusion injury (HIRI) often occurs in liver surgery, such as partial hepatectomy and liver transplantation, in which myeloid macrophage-mediated inflammation plays a critical role. Cell division cycle 42 (Cdc42) regulates cell migration, cytoskeleton rearrangement, and cell polarity. In this study, we explore the role of myeloid Cdc42 in HIRI. METHODS: Mouse HIRI models were established with 1-hour ischemia followed by 12-hour reperfusion in myeloid Cdc42 knockout (Cdc42mye) and Cdc42flox mice. Myeloid-derived macrophages were traced with RosamTmG fluorescent reporter under LyzCre-mediated excision. The experiments for serum or hepatic enzymic activities, histologic and immunologic analysis, gene expressions, flow cytometry analysis, and cytokine antibody array were performed. RESULTS: Myeloid deletion of Cdc42 significantly alleviated hepatic damages with the reduction of hepatic necrosis and inflammation, and reserved hepatic functions following HIRI in mice. Myeloid Cdc42 deficiency suppressed the infiltration of myeloid macrophages, reduced the secretion of proinflammatory cytokines, restrained M1 polarization, and promoted M2 polarization of myeloid macrophages in livers. In addition, inactivation of Cdc42 promoted M2 polarization via suppressing the phosphorylation of STAT1 and promoting phosphorylation of STAT3 and STAT6 in myeloid macrophages. Furthermore, pretreatment with Cdc42 inhibitor, ML141, also protected mice from hepatic ischemia-reperfusion injury. CONCLUSIONS: Inhibition or deletion of myeloid Cdc42 protects liver from HIRI via restraining the infiltration of myeloid macrophages, suppressing proinflammatory response, and promoting M2 polarization in macrophages.

The distinct localization of CDC42 isoforms is responsible for their specific functions during migration.

The small G-protein CDC42 is an evolutionary conserved polarity protein and a key regulator of polarized cell functions, including directed cell migration. In vertebrates, alternative splicing gives rise to two CDC42 proteins: the ubiquitously expressed isoform (CDC42u) and the brain isoform (CDC42b), which only differ in their carboxy-terminal sequence, including the CAAX motif essential for their association with membranes. We show that these divergent sequences do not directly affect the range of CDC42's potential binding partners but indirectly influence CDC42-driven signaling by controlling the subcellular localization of the two isoforms. In astrocytes and neural precursors, which naturally express both variants, CDC42u associates with the leading-edge plasma membrane of migrating cells, where it recruits the Par6-PKCζ complex to fulfill its polarity function. In contrast, CDC42b mainly localizes to intracellular membrane compartments, where it regulates N-WASP-mediated endocytosis. Both CDC42 isoforms contribute their specific functions to promote the chemotaxis of neural precursors, demonstrating that their expression pattern is decisive for tissue-specific cell behavior.

A Natural Small Molecule Mitigates Kidney Fibrosis by Targeting Cdc42-mediated GSK-3ß/ß-catenin Signaling.

Kidney fibrosis is a common fate of chronic kidney diseases (CKDs), eventually leading to renal dysfunction. Yet, no effective treatment for this pathological process has been achieved. During the bioassay-guided chemical investigation of the medicinal plant Wikstroemia chamaedaphne, a daphne diterpenoid, daphnepedunin A (DA), is characterized as a promising anti-renal fibrotic lead. DA shows significant anti-kidney fibrosis effects in cultured renal fibroblasts and unilateral ureteral obstructed mice, being more potent than the clinical trial drug pirfenidone. Leveraging the thermal proteome profiling strategy, cell division cycle 42 (Cdc42) is identified as the direct target of DA. Mechanistically, DA targets to reduce Cdc42 activity and down-regulates its downstream phospho-protein kinase Cζ(p-PKCζ)/phospho-glycogen synthase kinase-3ß (p-GSK-3ß), thereby promoting ß-catenin Ser33/37/Thr41 phosphorylation and ubiquitin-dependent proteolysis to block classical pro-fibrotic ß-catenin signaling. These findings suggest that Cdc42 is a promising therapeutic target for kidney fibrosis, and highlight DA as a potent Cdc42 inhibitor for combating CKDs.

RhoU forms homo-oligomers to regulate cellular responses.

RhoU is an atypical member of the Rho family of small G-proteins, which has N- and C-terminal extensions compared to the classic Rho GTPases RhoA, Rac1 and Cdc42, and associates with membranes through C-terminal palmitoylation rather than prenylation. RhoU mRNA expression is upregulated in prostate cancer and is considered a marker for disease progression. Here, we show that RhoU overexpression in prostate cancer cells increases cell migration and invasion. To identify RhoU targets that contribute to its function, we found that RhoU homodimerizes in cells. We map the region involved in this interaction to the C-terminal extension and show that C-terminal palmitoylation is required for self-association. Expression of the isolated C-terminal extension reduces RhoU-induced activation of p21-activated kinases (PAKs), which are known downstream targets for RhoU, and induces cell morphological changes consistent with inhibiting RhoU function. Our results show for the first time that the activity of a Rho family member is stimulated by self-association, and this is important for its activity.

Salmonella engages CDC42 effector protein 1 for intracellular invasion.

Human enterocytes are primary targets of infection by invasive bacterium Salmonella Typhimurium, and studies using nonintestinal epithelial cells established that S. Typhimurium activates Rho family GTPases, primarily CDC42, to modulate the actin cytoskeletal network for invasion. The host intracellular protein network that engages CDC42 and influences the pathogen's invasive capacity are relatively unclear. Here, proteomic analyses of canonical and variant CDC42 interactomes identified a poorly characterized CDC42 interacting protein, CDC42EP1, whose intracellular localization is rapidly redistributed and aggregated around the invading bacteria. CDC42EP1 associates with SEPTIN-7 and Villin, and its relocalization and bacterial engagement depend on host CDC42 and S. Typhimurium's capability of activating CDC42. Unlike CDC42, CDC42EP1 is not required for S. Typhimurium's initial cellular entry but is found to associate with Salmonella-containing vacuoles after long-term infections, indicating a contribution to the pathogen's intracellular growth and replication. These results uncover a new host regulator of enteric Salmonella infections, which may be targeted to restrict bacterial load at the primary site of infection to prevent systemic spread.

Cdc42 activity in the trailing edge is required for persistent directional migration of keratinocytes.

Fibroblasts migrate discontinuously by generating transient leading-edge protrusions and irregular, abrupt retractions of a narrow trailing edge. In contrast, keratinocytes migrate persistently and directionally via a single, stable, broad protrusion paired with a stable trailing-edge. The Rho GTPases Rac1, Cdc42 and RhoA are key regulators of cell protrusions and retractions. However, how these molecules mediate cell-type specific migration modes is still poorly understood. In fibroblasts, all three Rho proteins are active at the leading edge, suggesting short-range coordination of protrusive Rac1 and Cdc42 signals with RhoA retraction signals. Here, we show that Cdc42 was surprisingly active in the trailing-edge of migrating keratinocytes. Elevated Cdc42 activity colocalized with the effectors MRCK and N-WASP suggesting that Cdc42 controls both myosin activation and actin polymerization in the back. Indeed, Cdc42 was required to maintain the highly dynamic contractile acto-myosin retrograde flow at the trailing edge of keratinocytes, and its depletion induced ectopic protrusions in the back, leading to decreased migration directionality. These findings suggest that Cdc42 is required to stabilize the dynamic cytoskeletal polarization in keratinocytes, to enable persistent, directional migration.

Rho GTPase activity crosstalk mediated by Arhgef11 and Arhgef12 coordinates cell protrusion-retraction cycles.

Rho GTPases play a key role in the spatio-temporal coordination of cytoskeletal dynamics during cell migration. Here, we directly investigate crosstalk between the major Rho GTPases Rho, Rac and Cdc42 by combining rapid activity perturbation with activity measurements in mammalian cells. These studies reveal that Rac stimulates Rho activity. Direct measurement of spatio-temporal activity patterns show that Rac activity is tightly and precisely coupled to local cell protrusions, followed by Rho activation during retraction. Furthermore, we find that the Rho-activating Lbc-type GEFs Arhgef11 and Arhgef12 are enriched at transient cell protrusions and retractions and recruited to the plasma membrane by active Rac. In addition, their depletion reduces activity crosstalk, cell protrusion-retraction dynamics and migration distance and increases migration directionality. Thus, our study shows that Arhgef11 and Arhgef12 facilitate exploratory cell migration by coordinating cell protrusion and retraction by coupling the activity of the associated regulators Rac and Rho.

Longitudinal change in CDC42 in psoriasis: correlation with disease activity and treatment response.

Objective: To investigate longitudinal CDC42 change and its correlation with disease activity and treatment response in patients with psoriasis. Methods: This prospective study detected serum CDC42 at months (M) 0, M1, M3 and M6 in 150 patients with psoriasis with current initiation of topical therapy/phototherapy/systemic therapy. Results: CDC42 was positively related to systemic biologic treatment history (p = 0.025) but negatively associated with psoriatic area (p = 0.010) and Psoriasis Area Severity Index (PASI; p < 0.001). CDC42 continuously elevated from M0 to M6 (p < 0.001). CDC42 at M1/M3/M6 was enhanced in patients with current systemic biologic therapy and PASI 75 or 90 response at M6 versus those without (all p < 0.050). Conclusion: Increased serum CDC42 level reflects reduced disease severity and better treatment response in patients with psoriasis.

CDC42 is a protein that plays a role in inflammation and immune regulation in autoimmune diseases. CDC42 levels were detected in 150 patients with psoriasis at different time points and 150 healthy people at enrollment. The results showed that patients with psoriasis had lower CDC42 levels versus healthy people. Patients with psoriasis who received previous biologic treatments and those with smaller affected skin areas had higher CDC42 levels. Over time, CDC42 levels increased in patients with psoriasis. Patients who started biologic treatments (versus those who did not) and patients who responded better to treatment had higher CDC42 levels. The increase in CDC42 levels reflects better treatment outcomes in patients with psoriasis.

C-terminal variants in CDC42 drive type I interferon-dependent autoinflammation in NOCARH syndrome reversible by ruxolitinib.

C-terminal variants in CDC42 encoding cell division control protein 42 homolog underlie neonatal-onset cytopenia, autoinflammation, rash, and hemophagocytic lymphohistiocytosis (NOCARH). Pyrin inflammasome hyperactivation has been shown to contribute to disease pathophysiology. However, mortality of NOCARH patients remains high despite inflammasome-focused treatments. Here, we demonstrate in four NOCARH patients from three families that cell-intrinsic activation of type I interferon (IFN) is a previously unrecognized driver of autoinflammation in NOCARH. Our data show that aberrant innate immune activation is caused by sensing of cytosolic nucleic acids released from mitochondria, which exhibit disturbances in integrity and dynamics due to CDC42 dysfunction. In one of our patients, treatment with the Janus kinase inhibitor ruxolitinib led to complete remission, indicating that inhibition of type I IFN signaling may have an important role in the management of autoinflammation in patients with NOCARH.

Overexpression of microRNA-130a-3p suppresses glucose lipid levels and oxidative damage in diabetic retinopathy mice via modulating cell division cycle 42.

MicroRNA (miR)-130a-3p has been unraveled to exert effects on diabetes. However, the research for probing its role in diabetic retinopathy (DR) is limited. Our study intends to unravel the regulatory effects of miR-130a-3p on DR development via cell division cycle 42 (CDC42). The DR mouse model was established and the serum sample of DR patients was collected. The levels of miR- 130a-3p and CDC42 in DR mice and patients were detected. The nucleic acids modified miR-130a-3p or CDC42 were injected into DR mice to examine the change of glucose lipid levels, visual acuity, oxidative response and the distribution and expression of CDC42 in retinal tissues in DR mice. The target relationship between miR-130a-3p and CDC42 was confirmed. MiR-130a-3p expression was reduced while CDC42 levels were elevated in DR (P<0.05). The upregulation of miR-130a-3p could hinder glucose lipid levels, improve the visual acuity, relieve the oxidative response and decrease CDC42 expression levels in DR mice (P<0.05). The CDC42 elevation reversed the positive effects of upregulated miR-130a-3p on DR progression (P<0.05). MiR-130a-3p targeted CDC42. The elevated miR-130a-3p relieves glucose lipid levels and oxidative damage in DR by modulating CDC42. The study provides novel therapeutic targets for DR treatment.

The Role of ARHGAP1 in Rho GTPase Inactivation during Metastasizing of Breast Cancer Cell Line MCF-7 after Treatment with Doxorubicin.

Breast cancer is the most prevalent cancer type in women worldwide. It proliferates rapidly and can metastasize into farther tissues at any stage due to the gradual invasiveness and motility of the tumor cells. These crucial properties are the outcome of the weakened intercellular adhesion, regulated by small guanosine triphosphatases (GTPases), which hydrolyze to the guanosine diphosphate (GDP)-bound conformation. We investigated the inactivating effect of ARHGAP1 on Rho GTPases involved signaling pathways after treatment with a high dose of doxorubicin. Label-free quantitative proteomic analysis of the proteome isolated from the MCF-7 breast cancer cell line, treated with 1 µM of doxorubicin, identified RAC1, CDC42, and RHOA GTPases that were inactivated by the ARHGAP1 protein. Upregulation of the GTPases involved in the transforming growth factor-beta (TGF-beta) signaling pathway initiated epithelial-mesenchymal transitions. These findings demonstrate a key role of the ARHGAP1 protein in the disruption of the cell adhesion and simultaneously allow for a better understanding of the molecular mechanism of the reduced cell adhesion leading to the subsequent metastasis. The conclusions of this study corroborate the hypothesis that chemotherapy with doxorubicin may increase the risk of metastases in drug-resistant breast cancer cells.

BORG family proteins in physiology and human disease.

The binder of rho GTPases (BORG)/Cdc42 effector proteins (Cdc42EP) family is composed of five Rho GTPase binding proteins whose functions and mechanism of actions are of emerging interest. Here, we review recent findings pertaining to the family as a whole and consider how these change our understanding of cellular organization. Recent studies have implicated BORGs in both fundamental physiology and in human diseases, mainly cancers. An emerging pattern suggests that BORG family members cancer-promoting properties are related to their ability to regulate the cytoskeleton, with many impacting the organization of acto-myosin stress fibers. This is consistent with the broader literature indicating that BORG family members are regulators of both the septin and actin cytoskeleton networks. The exact mechanism through which BORGs modify the cytoskeleton is not clear, but we consider here a few data-supported and speculative possibilities. Finally, we delve into how the Rho GTPase Cdc42 modifies BORG function in cells. This remains open-ended as Cdc42's effects on BORGs appear cell type- and cell state-dependent. Collectively, these data point to the importance of the BORG family and suggest broader themes in their function and regulation.

Molecular dynamics simulations reveal the inhibition mechanism of Cdc42 by RhoGDI1.

Cell division control protein 42 homolog (Cdc42), which controls a variety of cellular functions including rearrangements of the cell cytoskeleton, cell differentiation and proliferation, is a potential cancer therapeutic target. As an endogenous negative regulator of Cdc42, the Rho GDP dissociation inhibitor 1 (RhoGDI1) can prevent the GDP/GTP exchange of Cdc42 to maintain Cdc42 into an inactive state. To investigate the inhibition mechanism of Cdc42 through RhoGDI1 at the atomic level, we performed molecular dynamics (MD) simulations. Without RhoGDI1, Cdc42 has more flexible conformations, especially in switch regions which are vital for binding GDP/GTP and regulators. In the presence of RhoGDI1, it not only can change the intramolecular interactions of Cdc42 but also can maintain the switch regions into a closed conformation through extensive interactions with Cdc42. These results which are consistent with findings of biochemical and mutational studies provide deep structural insights into the inhibition mechanisms of Cdc42 by RhoGDI1. These findings are beneficial for the development of novel therapies targeting Cdc42-related cancers.

ACKnowledging the role of the Activated-Cdc42 associated kinase (ACK) in regulating protein stability in cancer.

Activated Cdc42-associated kinase (ACK), a non-receptor tyrosine kinase, is an effector for the small GTPase Cdc42. ACK is emerging as an important component of the cancer landscape and thus, a promising target for the treatment of many malignancies. ACK is also being increasingly recognized as a potentially influential player in the regulation of protein homoeostasis. The delicate equilibrium between protein synthesis and protein degradation is crucial for healthy cell function and dysregulation of protein homoeostasis is a common occurrence in human disease. Here, we review the molecular mechanisms by which ACK regulates the stability of diverse cellular proteins (e.g. EGFR, p27, p53, p85 isoforms and RhoGDI-3), some of which rely on the kinase activity of ACK while others, interestingly, do not. Ultimately, further research will be required to bridge our knowledge gaps and determine if ACK regulates the stability of further cellular proteins but collectively, such mechanistic interrogation would contribute to determining whether ACK is a promising target for anti-cancer therapy. In therapeutics, proteasome inhibitors are an efficacious but problematic class of drugs. Targeting other modulators of proteostasis, like ACK, could open novel avenues for intervention.