Regulation of Cdc42 and its effectors in epithelial morphogenesis

Blood-testis barrier: a review on regulators in maintaining cell junction integrity between Sertoli cells

The blood-testis barrier (BTB) is formed adjacent to the seminiferous basement membrane. It is a distinct ultrastructure, partitioning testicular seminiferous epithelium into apical (adluminal) and basal compartments. It plays a vital role in developing and maturing spermatocytes into spermatozoa via reorganizing its structure. This enables the transportation of preleptotene spermatocytes across the BTB, from basal to adluminal compartments in the seminiferous tubules. Several bioactive peptides and biomolecules secreted by testicular cells regulate the BTB function and support spermatogenesis. These peptides activate various downstream signaling proteins and can also be the target themself, which could improve the diffusion of drugs across the BTB. The gap junction (GJ) and its coexisting junctions at the BTB maintain the immunological barrier integrity and can be the "gateway" during spermatocyte transition. These junctions are the possible route for toxicant entry, causing male reproductive dysfunction. Herein, we summarize the detailed mechanism of all the regulators playing an essential role in the maintenance of the BTB, which will help researchers to understand and find targets for drug delivery inside the testis.

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.

Physiological and transcriptomic analysis dissects the molecular mechanism governing meat quality during postmortem aging in Hu sheep (Ovis aries)

Introduction

Hu sheep, known for its high quality and productivity, lack fundamental scientific research in China.

Methods

This study focused on the effects of 24 h postmortem aging on the meat physiological and transcriptomic alteration in Hu sheep.

Results

The results showed that the 24 h aging process exerts a substantial influence on the mutton color, texture, and water content as compared to untreated group. Transcriptomic analysis identified 1,668 differentially expressed genes. Functional enrichment analysis highlighted the importance of glycolysis metabolism, protein processing in endoplasmic reticulum, and the FcγR-mediated phagocytosis pathway in mediating meat quality modification following postmortem aging. Furthermore, protein-protein interaction analysis uncovered complex regulatory networks involving glycolysis, the MAPK signaling pathway, protein metabolism, and the immune response.

Discussion

Collectively, these findings offer valuable insights into the molecular mechanisms underlying meat quality changes during postmortem aging in Hu sheep, emphasizing the potential for improving quality control strategies in mutton production.

The Role of Cdc42 in the Insulin and Leptin Pathways Contributing to the Development of Age-Related Obesity

Age-related obesity significantly increases the risk of chronic diseases such as type 2 diabetes, cardiovascular diseases, hypertension, and certain cancers. The insulin-leptin axis is crucial in understanding metabolic disturbances associated with age-related obesity. Rho GTPase Cdc42 is a member of the Rho family of GTPases that participates in many cellular processes including, but not limited to, regulation of actin cytoskeleton, vesicle trafficking, cell polarity, morphology, proliferation, motility, and migration. Cdc42 functions as an integral part of regulating insulin secretion and aging. Some novel roles for Cdc42 have also been recently identified in maintaining glucose metabolism, where Cdc42 is involved in controlling blood glucose levels in metabolically active tissues, including skeletal muscle, adipose tissue, pancreas, etc., which puts this protein in line with other critical regulators of glucose metabolism. Importantly, Cdc42 plays a vital role in cellular processes associated with the insulin and leptin signaling pathways, which are integral elements involved in obesity development if misregulated. Additionally, a change in Cdc42 activity may affect senescence, thus contributing to disorders associated with aging. This review explores the complex relationships among age-associated obesity, the insulin-leptin axis, and the Cdc42 signaling pathway. This article sheds light on the vast molecular web that supports metabolic dysregulation in aging people. In addition, it also discusses the potential therapeutic implications of the Cdc42 pathway to mitigate obesity since some new data suggest that inhibition of Cdc42 using antidiabetic drugs or antioxidants may promote weight loss in overweight or obese patients.

Membrane extraction in native lipid nanodiscs reveals dynamic regulation of Cdc42 complexes during cell polarization

Embryonic development requires the establishment of cell polarity to enable cell fate segregation and tissue morphogenesis. This process is regulated by Par complex proteins, which partition into polarized membrane domains and direct downstream polarized cell behaviors. The kinase aPKC (along with its cofactor Par6) is a key member of this network and can be recruited to the plasma membrane by either the small GTPase Cdc42 or the scaffolding protein Par3. Although in vitro interactions among these proteins are well established, much is still unknown about the complexes they form during development. Here, to enable the study of membrane-associated complexes ex vivo, we used a maleic acid copolymer to rapidly isolate membrane proteins from single C. elegans zygotes into lipid nanodiscs. We show that native lipid nanodisc formation enables detection of endogenous complexes involving Cdc42, which are undetectable when cells are lysed in detergent. We found that Cdc42 interacts more strongly with aPKC/Par6 during polarity maintenance than polarity establishment, two developmental stages that are separated by only a few minutes. We further show that Cdc42 and Par3 do not bind aPKC/Par6 simultaneously, confirming recent in vitro findings in an ex vivo context. Our findings establish a new tool for studying membrane-associated signaling complexes and reveal an unexpected mode of polarity regulation via Cdc42.

CDC42-mediated Wnt signaling facilitates odontogenic differentiation of DPCs during tooth root elongation

BACKGROUND

CDC42 is a member of Rho GTPase family, acting as a molecular switch to regulate cytoskeleton organization and junction maturation of epithelium in organ development. Tooth root pattern is a highly complicated and dynamic process that dependens on interaction of epithelium and mesenchyme. However, there is a lack of understanding of the role of CDC42 during tooth root elongation.

METHODS

The dynamic expression of CDC42 was traced during tooth development through immunofluorescence staining. Then we constructed a model of lentivirus or inhibitor mediated Cdc42 knockdown in Herwig's epithelial root sheath (HERS) cells and dental papilla cells (DPCs), respectively. Long-term influence of CDC42 abnormality was assessed via renal capsule transplantation and in situ injection of alveolar socket.

RESULTS

CDC42 displayed a dynamic spatiotemporal pattern, with abundant expression in HERS cells and apical DPCs in developing root. Lentivirus-mediated Cdc42 knockdown in HERS cells didn't disrupt cell junctions as well as epithelium-mesenchyme transition. However, inhibition of CDC42 in DPCs undermined cell proliferation, migration and odontogenic differentiation. Wnt/β-catenin signaling as the downstream target of CDC42 modulated DPCs' odontogenic differentiation. The transplantation and in situ injection experiments verified that loss of CDC42 impeded root extension via inhibiting the proliferation and differentiation of DPCs.

CONCLUSIONS

We innovatively revealed that CDC42 was responsible for guiding root elongation in a mesenchyme-specific manner. Furthermore, CDC42-mediated canonical Wnt signaling regulated odontogenic differentiation of DPCs during root formation.

Serum CDC42 reflects the exacerbation risk and severity, Th1/2 cell imbalance and inflammation in asthmatic children

Aim: To explore the clinical implication of serum CDC42 in asthmatic children. Materials & methods: Serum CDC42 from 80 asthmatic children experiencing exacerbation, 80 asthmatic children in remission and 40 healthy controls was detected by ELISA. Results: CDC42 was highest in asthmatic children experiencing exacerbation followed by asthmatic children in remission and healthy controls (p < 0.001). Among asthmatic children experiencing exacerbation, CDC42 positively correlated with exacerbation severity (p = 0.011), Th2 (p = 0.017), TNF-α (p < 0.001), IL-6 (p = 0.009) and IL-8 (p = 0.008) and negatively correlated with Th1/Th2 ratio (p = 0.028). In asthmatic children in remission, CDC42 correlated with lower Th1/Th2 ratio (p = 0.028) and higher TNF-α (p = 0.026). In healthy controls, CDC42 showed no correlation with Th1/2 or inflammatory cytokines. Conclusion: Circulating CDC42 reflects exacerbation risk, Th1/2 imbalance and inflammation in asthmatic children.

A ubiquitin-based effector-to-inhibitor switch coordinates early brain, craniofacial, and skin development

The molecular mechanisms that coordinate patterning of the embryonic ectoderm into spatially distinct lineages to form the nervous system, epidermis, and neural crest-derived craniofacial structures are unclear. Here, biochemical disease-variant profiling reveals a posttranslational pathway that drives early ectodermal differentiation in the vertebrate head. The anteriorly expressed ubiquitin ligase CRL3-KLHL4 restricts signaling of the ubiquitous cytoskeletal regulator CDC42. This regulation relies on the CDC42-activating complex GIT1-βPIX, which CRL3-KLHL4 exploits as a substrate-specific co-adaptor to recognize and monoubiquitylate PAK1. Surprisingly, we find that ubiquitylation converts the canonical CDC42 effector PAK1 into a CDC42 inhibitor. Loss of CRL3-KLHL4 or a disease-associated KLHL4 variant reduce PAK1 ubiquitylation causing overactivation of CDC42 signaling and defective ectodermal patterning and neurulation. Thus, tissue-specific restriction of CDC42 signaling by a ubiquitin-based effector-to-inhibitor is essential for early face, brain, and skin formation, revealing how cell-fate and morphometric changes are coordinated to ensure faithful organ development.

Pericyte-Glioblastoma Cell Interaction: A Key Target to Prevent Glioblastoma Progression

Multiple biological processes rely on direct intercellular interactions to regulate cell proliferation and migration in embryonic development and cancer processes. Tumor development and growth depends on close interactions between cancer cells and cells in the tumor microenvironment. During embryonic development, morphogenetic signals and direct cell contacts control cell proliferation, polarity, and morphogenesis. Cancer cells communicate with cells in the tumor niche through molecular signals and intercellular contacts, thereby modifying the vascular architecture and antitumor surveillance processes and consequently enabling tumor growth and survival. While looking for cell-to-cell signaling mechanisms that are common to both brain development and cancer progression, we have studied the infiltration process in glioblastoma multiforme (GBM), which is the most malignant primary brain tumor and with the worst prognosis. Cell-to-cell contacts, by means of filopodia-like structures, between GBM cells and brain pericytes (PCs) are necessary for adequate cell signaling during cancer infiltration; similarly, contacts between embryonic regions, via cytonemes, are required for embryo regionalization and development. This GBM-PC interaction provokes two important changes in the physiological function of these perivascular cells, namely, (i) vascular co-option with changes in cell contractility and vascular malformation, and (ii) changes in the PC transcriptome, modifying the microvesicles and protein secretome, which leads to the development of an immunosuppressive phenotype that promotes tumor immune tolerance. Moreover, the GTPase Cdc42 regulates cell polarity across organisms, from yeast to humans, playing a central role in GBM cell-PC interaction and maintaining vascular co-option. As such, a review of the molecular and cellular mechanisms underlying the development and maintenance of the physical interactions between cancer cells and PCs is of particular interest.

Stress-induced cell depolarization through the MAP kinase-Cdc42 axis

General stress responses, which sense environmental or endogenous signals, aim at promoting cell survival and fitness during adverse conditions. In eukaryotes, mitogen-activated protein (MAP) kinase-driven cascades trigger a shift in the cell's gene expression program as a cellular adaptation to stress. Here, we review another aspect of activated MAP kinase cascades reported in fission yeast: the transient inhibition of cell polarity in response to oxidative stress. The phosphorylation by a stress-activated MAP kinase of regulators of the GTPase cell division cycle 42 (Cdc42) causes a transient inhibition of polarized cell growth. The formation of growth sites depends on limiting and essential polarity components. We summarize here some processes in which inhibition of Cdc42 may be a general mechanism to regulate polarized growth also under physiological conditions.

Role of a small GTPase Cdc42 in aging and age-related diseases

A small GTPase, Cdc42 is evolutionarily one of the most ancient members of the Rho family, which is ubiquitously expressed and involved in a wide range of fundamental cellular functions. The crucial role of Cdc42 includes regulation of the actin cytoskeleton, cell polarity, morphology and migration, endocytosis and exocytosis, cell cycle, and proliferation in many different cell types. Many studies have provided compelling yet contradicting evidence that Cdc42 dysregulation plays an important role in cellular and tissue aging. Furthermore, Cdc42 is a critical factor in the development and progression of aging-related pathologies, such as neurodegenerative and cardiovascular disorders, diabetes type 2, and aging-related disorders of the joints and bones, and the inhibition of the Cdc42 demonstrates potentially significant therapeutic and anti-aging effects in animal models of aging and disease. However, regulation of Cdc42 expression and activity is very complex and depends on many factors, such as the origin and complexity of the tissues, hormonal status, etc. Therefore, this review is focused on current advances in understanding the underlying cellular and molecular mechanisms associated with Cdc42 activity and regulation of senescence in different cell types since they may provide a foundation for novel therapeutic strategies and targeted drugs to reverse the aging process and treat aging-associated disorders.

The clinical role of serum cell division control 42 in coronary heart disease

Cell division control 42 (CDC42) regulates blood lipids, atherosclerosis, T cell differentiation and inflammation, which is involved in the process of coronary heart disease (CHD). This study aimed to evaluate the CDC42 level and its correlation with clinical features, the T-helper 17 (Th17)/regulatory-T (Treg) cell ratio and prognosis in CHD patients. In total, 210 CHD patients, 20 healthy controls and 20 disease controls were enrolled. Serum CDC42 levels of all participants were measured by enzyme-linked immunosorbent assay. In CHD patients, Th17 and Treg cells were discovered by flow cytometry; CHD patients were followed-up for a median of 16.9 months (range of 2.5-38.2 months). CDC42 level was lowest in CHD patients (median (interquartile range (IQR)): 402.5 (287.3-599.0) pg/mL), moderate in disease controls (median (IQR): 543.5 (413.0-676.3) pg/mL) and highest in healthy controls (median (IQR): 668.0 (506.5-841.3) pg/mL) (p < .001). Moreover, in CHD patients, lower CDC42 level was related to more prevalent diabetes mellitus (p = .021), and higher levels of C-reactive protein (p = .001), Gensini score (p = .006), Th17 cells (p = .001) and Th17/Treg ratio (p < .001) but was associated with lower Treg cells (p = .018). Furthermore, CDC42 low level [below the median level (402.5 pg/mL) of CDC42 in CHD patients] was correlated with higher accumulating major adverse cardiovascular event (MACE) risk (p = .029), while no correlation was found between the quartile of CDC42 level and accumulating MACE risk in CHD patients (p = .102). The serum CDC42 level is decreased and its low level is related to higher Th17/Treg ratio and increased accumulating MACE risk in CHD patients.

Role of phosphatidylserine in the localization of cell surface membrane proteins in yeast

Phosphatidylserine (PS) is a constituent of the cell membrane, being especially abundant in the cytoplasmic leaflet, and plays important roles in a number of cellular functions, including the formation of cell polarity and intracellular vesicle transport. Several studies in mammalian cells have suggested the role of PS in retrograde membrane traffic through endosomes, but in yeast, where PS is localized primarily at the plasma membrane (PM), the role in intracellular organelles remains unclear. Additionally, it is reported that polarized endocytic site formation is defective in PS-depleted yeast cells, but the role in the endocytic machinery has not been well understood. In this study, to clarify the role of PS in the endocytic pathway, we analyzed the effect of PS depletion on endocytic internalization and post-endocytic transport. We demonstrated that in cell lacking the PS synthase Cho1p (cho1Δ cell), binding and internalization of mating pheromone α-factor into the cell was severely impaired. Interestingly, the processes of endocytosis were mostly unaffected, but protein transport from the trans-Golgi network (TGN) to the PM was defective and localization of cell surface proteins was severely impaired in cho1Δ cells. We also showed that PS accumulated in intracellular compartments in cells lacking Rcy1p and Vps52p, both of which are implicated in endosome-to-PM transport via the TGN, and that the number of Snx4p-residing endosomes was increased in cho1Δ cells. These results suggest that PS plays a crucial role in the transport and localization of cell surface membrane proteins.Key words: phosphatidylserine, endocytosis, recycling, vesicle transport.

pTINCR microprotein promotes epithelial differentiation and suppresses tumor growth through CDC42 SUMOylation and activation

The human transcriptome contains thousands of small open reading frames (sORFs) that encode microproteins whose functions remain largely unexplored. Here, we show that TINCR lncRNA encodes pTINCR, an evolutionary conserved ubiquitin-like protein (UBL) expressed in many epithelia and upregulated upon differentiation and under cellular stress. By gain- and loss-of-function studies, we demonstrate that pTINCR is a key inducer of epithelial differentiation in vitro and in vivo. Interestingly, low expression of TINCR associates with worse prognosis in several epithelial cancers, and pTINCR overexpression reduces malignancy in patient-derived xenografts. At the molecular level, pTINCR binds to SUMO through its SUMO interacting motif (SIM) and to CDC42, a Rho-GTPase critical for actin cytoskeleton remodeling and epithelial differentiation. Moreover, pTINCR increases CDC42 SUMOylation and promotes its activation, triggering a pro-differentiation cascade. Our findings suggest that the microproteome is a source of new regulators of cell identity relevant for cancer.

aPKC regulates apical constriction to prevent tissue rupture in the Drosophila follicular epithelium

Apical-basal polarity is an essential epithelial trait controlled by the evolutionarily conserved PAR-aPKC polarity network. Dysregulation of polarity proteins disrupts tissue organization during development and in disease, but the underlying mechanisms are unclear due to the broad implications of polarity loss. Here, we uncover how Drosophila aPKC maintains epithelial architecture by directly observing tissue disorganization after fast optogenetic inactivation in living adult flies and ovaries cultured ex vivo. We show that fast aPKC perturbation in the proliferative follicular epithelium produces large epithelial gaps that result from increased apical constriction, rather than loss of apical-basal polarity. Accordingly, we can modulate the incidence of epithelial gaps by increasing and decreasing actomyosin-driven contractility. We traced the origin of these large epithelial gaps to tissue rupture next to dividing cells. Live imaging shows that aPKC perturbation induces apical constriction in non-mitotic cells within minutes, producing pulling forces that ultimately detach dividing and neighboring cells. We further demonstrate that epithelial rupture requires a global increase of apical constriction, as it is prevented by the presence of non-constricting cells. Conversely, a global induction of apical tension through light-induced recruitment of RhoGEF2 to the apical side is sufficient to produce tissue rupture. Hence, our work reveals that the roles of aPKC in polarity and actomyosin regulation are separable and provides the first in vivo evidence that excessive tissue stress can break the epithelial barrier during proliferation.

CDC42 governs normal oviduct multiciliogenesis through activating AKT to ensure timely embryo transport

Ciliated and secretory cells are two major cell types that comprise the oviduct epithelia. Accumulating evidences support a role of oviductal multiciliated epithelia for embryo transport, however the mechanisms underlying this specialized cell type differentiation remain elusive. Here, we report that CDC42 depletion in oviduct epithelia hampers the morphogenesis of multiciliated cell, and results in embryo retention, leading to early pregnancy failure. Utilizing the oviduct organoid model, we further observed that CDC42 guides secretory cells transition into multiciliated cells independent of its GTPase activity and the well-known Notch pathway. Further exploration uncovered the AKT as a novel indispensable regulator for multiciliated cells differentiation, whose activity was maintained by CDC42 through interacting with the p110β. Consistently, re-activating AKT partially incites multiciliated cells differentiation in Cdc42 knockout oviductal organoids. Finally, low levels of CDC42 and phospho-AKT with reduced multiciliated cells in the oviduct are observed in women with ectopic pregnancy. Collectively, we provide previously unappreciated evidence that CDC42-AKT signaling is a critical determinant for morphogenesis of oviduct multiciliated cell, which possesses the clinical application in understanding the pathology of ectopic pregnancy and facilitating the development of prevention strategies.

MRCKα is a novel regulator of prolactin-induced lactogenesis in bovine mammary epithelial cells

Myotonic dystrophy-related Cdc42-binding kinase alpha (MRCKα) is an integral component of signaling pathways controlling vital cellular processes, including cytoskeletal reorganization, cell proliferation and cell survival. In this study, we investigated the physiological role of MRCKα in milk protein and fat production in dairy cows, which requires a dynamic and strict organization of the cytoskeletal network in bovine mammary epithelial cells (BMEC). Within a selection of 9 Holstein cows, we found that both mRNA and protein expression of MRCKα in the mammary gland were upregulated during lactation and correlated positively (r > 0.89) with the mRNA and protein levels of β-casein. Similar positive correlations (r > 0.79) were found in a primary culture of BMEC stimulated with prolactin for 24 h. In these cells, silencing of MRCKα decreased basal β-casein, sterol-regulatory element binding protein (SREBP)-1 and cyclin D1 protein level, phosphorylation of mTOR, triglyceride secretion, cell number and viability-while overexpression of MRCKα displayed the reversed effect. Notably, silencing of MRCKα completely prevented the stimulatory action of prolactin on the same parameters. These data demonstrate that MRCKα is a critical mediator of prolactin-induced lactogenesis via stimulation of the mTOR/SREBP1/cyclin D1 signaling pathway.

Directed cell invasion and asymmetric adhesion drive tissue elongation and turning in C. elegans gonad morphogenesis

Development of the C. elegans gonad has long been studied as a model of organogenesis driven by collective cell migration. A somatic cell named the distal tip cell (DTC) is thought to serve as the leader of following germ cells; yet, the mechanism for DTC propulsion and maneuvering remains elusive. Here, we demonstrate that the DTC is not self-propelled but rather is pushed by the proliferating germ cells. Proliferative pressure pushes the DTC forward, against the resistance of the basement membrane in front. The DTC locally secretes metalloproteases that degrade the impeding membrane, resulting in gonad elongation. Turning of the gonad is achieved by polarized DTC-matrix adhesions. The asymmetrical traction results in a bending moment on the DTC. Src and Cdc42 regulate integrin adhesion polarity, whereas an external netrin signal determines DTC orientation. Our findings challenge the current view of DTC migration and offer a distinct framework to understand organogenesis.

Relation of CDC42, Th1, Th2, and Th17 cells with cognitive function decline in Alzheimer's disease

OBJECTIVE

Cell division cycle 42 (CDC42) regulates neurite outgrowth, neurotransmitter, and T help (Th) cell-mediated neuroinflammation, while its clinical implication in Alzheimer's disease (AD) is not clear. The present study aimed to investigate the correlation of CDC42 with Th1, Th2, and Th17 cells, as well as CDC42' longitudinal change and relation to cognitive function decline in AD patients.

METHODS

150 AD patients were enrolled, then their blood Th1, Th2, and Th17 cells were quantified by flow cytometry at baseline; CDC42 was detected by RT-qPCR and MMSE score was assessed at baseline and during 3-year follow-up. Meanwhile, CDC42, Th1, Th2, and Th17 cells were quantified in 30 Parkinson's disease (PD) patients and 30 healthy controls (HCs).

RESULTS

CDC42 (p < 0.001) and Th2 cells (p < 0.001) were lowest in AD patients, followed by PD patients, highest in HCs; but Th1 cells (p = 0.001) and Th17 cells (p < 0.001) showed opposite trends. CDC42 was not related to Th1 cells (p = 0.134), positively correlated with Th2 cells (p = 0.023) and MMSE (p < 0.001), while negatively associated with Th17 cells (p < 0.001) in AD patients. CDC42 was only related to Th17 cells (p = 0.048) and MMSE (p = 0.048) in PD patients; and it was not linked with Th1, Th2, Th17 cells, or MMSE in HCs (all p > 0.05). During a 3-year follow-up, CDC42 was gradually declined in AD patients (p < 0.001), its decline was positively correlated with MMSE decline at 1 year (p = 0.004), 2 years (p = 0.005), and 3 years (p = 0.026).

INTERPRETATION

CDC42 might have the potency to serve as a biomarker for estimating AD risk and progression.

Temporal analysis of enhancers during mouse cerebellar development reveals dynamic and novel regulatory functions

We have identified active enhancers in the mouse cerebellum at embryonic and postnatal stages which provides a view of novel enhancers active during cerebellar development. The majority of cerebellar enhancers have dynamic activity between embryonic and postnatal development. Cerebellar enhancers were enriched for neural transcription factor binding sites with temporally specific expression. Putative gene targets displayed spatially restricted expression patterns, indicating cell-type specific expression regulation. Functional analysis of target genes indicated that enhancers regulate processes spanning several developmental epochs such as specification, differentiation and maturation. We use these analyses to discover one novel regulator and one novel marker of cerebellar development: Bhlhe22 and Pax3, respectively. We identified an enrichment of de novo mutations and variants associated with autism spectrum disorder in cerebellar enhancers. Furthermore, by comparing our data with relevant brain development ENCODE histone profiles and cerebellar single-cell datasets we have been able to generalize and expand on the presented analyses, respectively. We have made the results of our analyses available online in the Developing Mouse Cerebellum Enhancer Atlas (https://goldowitzlab.shinyapps.io/developing_mouse_cerebellum_enhancer_atlas/), where our dataset can be efficiently queried, curated and exported by the scientific community to facilitate future research efforts. Our study provides a valuable resource for studying the dynamics of gene expression regulation by enhancers in the developing cerebellum and delivers a rich dataset of novel gene-enhancer associations providing a basis for future in-depth studies in the cerebellum.

Cdc42 promotes thyroid cancer cell proliferation and migration and tumor-associated macrophage polarization through the PTEN/AKT pathway

The purpose of this study was to investigate the potential mechanism and function of Cdc42 in thyroid cancer. We found that knockdown of Cdc42 inhibited the migration and proliferation of WRO cells. This role of Cdc42 is achieved by interacting with PTEN and interfering with its PTEN nuclear translocation. The overexpression of Cdc42 enhances the production of lactic acid and promotes the polarization of M2 macrophages, and therefore M2 macrophages inhibit the function of T cells. Overall, Cdc42 can promote cell proliferation and migration through the PTEN/AKT pathway and promote tumor-related M2 macrophage polarization and inhibit T cell activity by enhancing aerobic glycolysis, animal experiments confirmed that tumor volume increased after Cdc42 overexpressed in TBP-3743 murine thyroid cancer cells. Increased infiltration of Treg and macrophages was also observed. taken together, our results indicate that Cdc42 can be used as a diagnostic and thyroid cancer Prognostic biomarkers and potential therapeutic targets.

Aberrant blood cell division cycle 42 expression and its correlation with disease severity, inflammation and mortality risk in patients with acute pancreatitis

Cell division cycle 42 (CDC42) can inhibit inflammation by regulating the activity of macrophage and T cells, which contributes to the pathophysiology of acute pancreatitis (AP). Therefore, CDC42 may have application as a potential biomarker for AP. The present study aimed to explore this possibility. Peripheral blood mononuclear cells (PBMCs) were collected from 149 patients with AP and 50 healthy controls (HCs). Subsequently, CDC42 expression in the PBMCs was measured using RT-qPCR; C-reactive protein (CRP), TNF-α and IL-6 in the serum of patients with AP were measured using ELISA. Meanwhile, Mann-Whitney U test, Kruskal-Wallis test, and Spearman's rank correlation test were performed on the data. The CDC42 expression levels were lower in patients with AP compared with those in HCs (P<0.001). CDC42 expression was declined in patients with moderate-severe AP (MSAP) vs. patients with mild AP (MAP) (P=0.029), and in patients with severe AP (SAP) vs. patients with MAP (P=0.004). CDC42 expression correlated negatively with the Ranson's score (P<0.001), APACEH II score (P=0.011) and SOFA score (P<0.001) in patients with AP. CDC42 expression also correlated negatively with CRP (P<0.001) and TNF-α (P=0.004) levels but not with IL-6 levels (P=0.177). Furthermore, CDC42 expression was lower in deceased patients with AP vs. AP survivors (P<0.001) and in deceased patients with SAP vs. SAP survivors (P=0.026). CDC42 had good potential in predicting mortality from AP, with AUC of 0.829 and a 95% CI of 0.731-0.927, and it also had certain potential in predicting mortality from SAP and MSAP, with AUC (95% CI) of 0.794 (0.616-0.973) and 0.757 (0.558-0.956), respectively. In conclusion, data from the present study suggest that lower CDC42 expression levels correlate with higher disease susceptibility, disease severity, inflammation, and mortality risk in patients with AP.

Juvenile hormone promotes paracellular transport of yolk proteins via remodeling zonula adherens at tricellular junctions in the follicular epithelium

Juvenile hormone (JH) acts as a gonadotrophic hormone stimulating insect vitellogenesis and oogenesis. Paracellular transport of yolk proteins through intercellular channels (patency) in the follicular epithelium is a developmentally regulated and evolutionarily conserved process during vitellogenesis. However, the mechanisms underlying patency opening are poorly understood. Using the migratory locust Locusta migratoria as a model system, we report here that JH-regulated remodeling of zonula adherens (ZA), the belt-like adherens junction maintaining physical linking between follicle cells controlled the opening of patency. JH triggered phosphorylation of Partitioning defective protein 3 (Par3) via a signaling cascade including G protein-coupled receptor (GPCR), small GTPase Cell division cycle 42 (Cdc42) and atypical Protein kinase C (aPKC). Par3 phosphorylation resulted in its disassociation from β-Catenin, the cytoplasmic partner of ZA core component E-Cadherin. Release of Par3 from the β-Catenin/E-Cadherin complex caused ZA disassembly at tricellular contacts, consequently leading to patency enlargement. This study provides new insight into how JH stimulates insect vitellogenesis and egg production via inducing the opening of paracellular route for vitellogenin transport crossing the follicular epithelium barrier.

Vitellogenesis is one of the most emblematic processes in female reproduction of oviparous animals. In many insects, the yolk protein precursor, vitellogenin (Vg) is synthesized in the fat body and transported to oocytes through the intercellular spaces (patency) among follicular cells. Juvenile hormone (JH), the arthropod-specific sesquiterpenoid plays a crucial role in paracellular Vg transport, but the molecular mechanisms of JH-stimulated patency remain elusive. In the present study, we show that JH acts via the GPCR-Cdc42-aPKC signaling cascade that triggers the phosphorylation of Par3, a critical scaffold protein of zonula adherens. JH-dependent Par3 phosphorylation results in its dissociation from the β-Catenin/E-Cadherin complex, consequently leading to patency opening for Vg transport. The findings reveal an important mechanism by which JH induces the remodeling of zonula adherens for the opening of paracellular route for Vg transport crossing the follicular epithelium barrier in the ovary.

The Roles of Par3, Par6, and aPKC Polarity Proteins in Normal Neurodevelopment and in Neurodegenerative and Neuropsychiatric Disorders

Normal neural circuits and functions depend on proper neuronal differentiation, migration, synaptic plasticity, and maintenance. Abnormalities in these processes underlie various neurodevelopmental, neuropsychiatric, and neurodegenerative disorders. Neural development and maintenance are regulated by many proteins. Among them are Par3, Par6 (partitioning defective 3 and 6), and aPKC (atypical protein kinase C) families of evolutionarily conserved polarity proteins. These proteins perform versatile functions by forming tripartite or other combinations of protein complexes, which hereafter are collectively referred to as "Par complexes." In this review, we summarize the major findings on their biophysical and biochemical properties in cell polarization and signaling pathways. We next summarize their expression and localization in the nervous system as well as their versatile functions in various aspects of neurodevelopment, including neuroepithelial polarity, neurogenesis, neuronal migration, neurite differentiation, synaptic plasticity, and memory. These versatile functions rely on the fundamental roles of Par complexes in cell polarity in distinct cellular contexts. We also discuss how cell polarization may correlate with subcellular polarization in neurons. Finally, we review the involvement of Par complexes in neuropsychiatric and neurodegenerative disorders, such as schizophrenia and Alzheimer's disease. While emerging evidence indicates that Par complexes are essential for proper neural development and maintenance, many questions on their in vivo functions have yet to be answered. Thus, Par3, Par6, and aPKC continue to be important research topics to advance neuroscience.

REPS2 downregulation facilitates FGF-induced adhesion and migration in human lens epithelial cells through FAK/Cdc42 signaling and contributes to posterior capsule opacification

Posterior capsular opacification (PCO) can cause postoperative visual loss after cataract surgery. Residual human lens epithelial cell (HLEC) proliferation, migration, epithelial-mesenchymal transition (EMT) and synthesis of extracellular matrix (ECM) are the entitative reasons for PCO. Low expression of Ral-binding protein 1-associated Eps domain-containing 2 (REPS2) and high levels of basic fibroblast growth factor (b-FGF) were observed in the lens and postoperative aqueous humor of cataract patients. REPS2 was identified as a negative regulator in growth factor signaling; however, its function in HLECs is unknown. This was first investigated in the present study by evaluating REPS2 expression in anterior lens capsules from cataract patients, a mouse cataract model, and HLE-b3 cells. The biological function of REPS2 in HLE-B3 cells was assessed by REPS2 silencing and Cell Counting Kit 8, wound healing, Transwell migration, F-actin staining, G-protein pulldown and western blot assays. In the present study, REPS2 was significantly downregulated in human and mouse cataract capsules and H₂O₂-treated HLE-B3 cells. REPS2 knockdown increased fibronectin, type I collagen, and α-smooth muscle actin expression levels and stimulated HLECs proliferation and migration; these effects were enhanced by FGF treatment and accompanied with focal adhesion kinase (FAK) phosphorylation, cell division cycle 42 (Cdc42) activation, focal adhesion protein upregulation, and F-actin cytoskeleton reorganization. However, treatment with the FAK inhibitor PF573228 abolished these effects. Thus, REPS2 downregulation in cataract HLECs induces their proliferation and facilitates FGF-induced ECM synthesis, EMT, cell adhesion and migration by activating FAK/Cdc42 signaling, which may underlie PCO pathogenesis.

Crumbs complex-directed apical membrane dynamics in epithelial cell ingression

Epithelial cells often leave their tissue context and ingress to form new cell types or acquire migratory ability to move to distant sites during development and tumor progression. Cells lose their apical membrane and epithelial adherens junctions during ingression. However, how factors that organize apical-basal polarity contribute to ingression is unknown. Here, we show that the dynamic regulation of the apical Crumbs polarity complex is crucial for normal neural stem cell ingression. Crumbs endocytosis and recycling allow ingression to occur in a normal timeframe. During early ingression, Crumbs and its complex partner the RhoGEF Cysts support myosin and apical constriction to ensure robust ingression dynamics. During late ingression, the E3-ubiquitin ligase Neuralized facilitates the disassembly of the Crumbs complex and the rapid endocytic removal of the apical cell domain. Our findings reveal a mechanism integrating cell fate, apical polarity, endocytosis, vesicle trafficking, and actomyosin contractility to promote cell ingression, a fundamental morphogenetic process observed in animal development and cancer.

Longitudinal Variations of CDC42 in Patients With Acute Ischemic Stroke During 3-Year Period: Correlation With CD4+ T Cells, Disease Severity, and Prognosis

Objective

Cell division cycle 42 (CDC42) modulates CD4⁺ T-cell differentiation, blood lipids, and neuronal apoptosis and is involved in the pathogenesis of acute ischemic stroke (AIS); however, the clinical role of CDC42 in AIS remains unanswered. This study aimed to evaluate the expression of CDC42 in a 3-year follow-up and its correlation with disease severity, T helper (Th)1/2/17 cells, and the prognosis in patients with AIS.

Methods

Blood CDC42 was detected in 143 patients with AIS at multiple time points during the 3-year follow-up period and in 70 controls at admission by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). In addition, blood Th1, Th2, and Th17 cells and their secreted cytokines (interferon-γ (IFN-γ), interleukin-4 (IL-4), and interleukin-17A (IL-17A)) in patients with AIS were detected by flow cytometry and enzyme-linked immunosorbent assay (ELISA), respectively.

Results

Compared with controls (p < 0.001), CDC42 was reduced in patients with AIS. CDC42 was negatively correlated with the National Institutes of Health Stroke Scale (NIHSS) score (p < 0.001), whereas, in patients with AIS (all p < 0.050), it was positively associated with Th2 cells and IL-4 but negatively correlated with Th17 cells and IL-17A. CDC42 was decreased from admission to 3 days and gradually increased from 3 days to 3 years in patients with AIS (P<0.001). In a 3-year follow-up, 24 patients with AIS recurred and 8 patients died. On the 3rd day, 7th day, 1st month, 3rd month, 6th month, 1st year, 2nd year, and 3rd year, CDC42 was decreased in recurrent patients than that in non-recurrent patients (all p < 0.050). CDC42 at 7 days (p = 0.033) and 3 months (p = 0.023) was declined in reported deceased patients than in survived patients.

Conclusion

CDC42 is used as a biomarker to constantly monitor disease progression and recurrence risk of patients with AIS.

Up-Regulated MISP Is Associated With Poor Prognosis and Immune Infiltration in Pancreatic Ductal Adenocarcinoma

Background

Pancreatic ductal adenocarcinoma (PDAC) is a highly malignant disease with a poor prognosis. More effective biomarkers and treatment options remain to be discovered. Mitotic Spindle Positioning (MISP), also called C19orf21, has been reported to be upregulated in several malignancies. However, the effects of MISP on PDAC have yet to be investigated.

Materials and Methods

The differential expression of MISP at the mRNA and protein levels were evaluated using Gene Expression Profiling Interactive Analysis 2 (GEPIA 2), Gene Expression Omnibus (GEO), and the Human Protein Atlas (HPA) databases, and was further verified by quantitative real-time PCR and western blotting in PDAC cell lines. Correlations between MISP expression and clinical characteristics were explored using Kaplan-Meier Plotter Database and clinical data from The Cancer Genome Atlas (TCGA). CCK-8 assays, Transwell assays, and immunoblotting were used to determine the role of MISP in PDAC proliferation, migration, invasion, and epithelial-mesenchymal transition (EMT) in vitro. Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis were executed by the R package ‘clusterProfiler’. Correlations between MISP expression and immune cell infiltration, immune checkpoints, immunophenoscore (IPS) and the tumor mutational burden (TMB) in PDAC were explored using the R package ‘CIBERSORT’, the Tumor Immune Estimation Resource 2.0 (TIMER2.0), and The Cancer Immunome Atlas (TCIA) database based on TCGA data.

Result

MISP expression was significantly higher in pancreatic cancer tissues compared to normal pancreas tissues, which was associated with a poor prognosis. Increased expression of MISP was related to the proliferation, migration and invasion of PDAC cell lines. GO and KEGG pathway analyses determined that MISP is involved in the Ras signaling pathway and immune regulation. Higher expression of MISP was associated with decreased infiltration levels of activated CD4+ memory T cells, CD8+ T cells, M2 macrophages and neutrophils. Furthermore, increased MISP was associated with lower expression of immune checkpoint molecules, higher gene mutation burden and IPS.

Conclusions

This study reveals that MISP, which is associated with the progression and prognosis of PDAC, may exert a potential regulatory effect on immune infiltration and predict the response to immunotherapy in PDAC.

Cdc42/Rac Interactive Binding Containing Effector Proteins in Unicellular Protozoans With Reference to Human Host: Locks of the Rho Signaling

Small GTPases are the key to actin cytoskeleton signaling, which opens the lock of effector proteins to forward the signal downstream in several cellular pathways. Actin cytoskeleton assembly is associated with cell polarity, adhesion, movement and other functions in eukaryotic cells. Rho proteins, specifically Cdc42 and Rac, are the primary regulators of actin cytoskeleton dynamics in higher and lower eukaryotes. Effector proteins, present in an inactive state gets activated after binding to the GTP bound Cdc42/Rac to relay a signal downstream. Cdc42/Rac interactive binding (CRIB) motif is an essential conserved sequence found in effector proteins to interact with Cdc42 or Rac. A diverse range of Cdc42/Rac and their effector proteins have evolved from lower to higher eukaryotes. The present study has identified and further classified CRIB containing effector proteins in lower eukaryotes, focusing on parasitic protozoans causing neglected tropical diseases and taking human proteins as a reference point to the highest evolved organism in the evolutionary trait. Lower eukaryotes’ CRIB containing proteins fall into conventional effector molecules, PAKs (p21 activated kinase), Wiskoit-Aldrich Syndrome proteins family, and some have unique domain combinations unlike any known proteins. We also highlight the correlation between the effector protein isoforms and their selective specificity for Cdc42 or Rac proteins during evolution. Here, we report CRIB containing effector proteins; ten in Dictyostelium and Entamoeba, fourteen in Acanthamoeba, one in Trypanosoma and Giardia. CRIB containing effector proteins that have been studied so far in humans are potential candidates for drug targets in cancer, neurological disorders, and others. Conventional CRIB containing proteins from protozoan parasites remain largely elusive and our data provides their identification and classification for further in-depth functional validations. The tropical diseases caused by protozoan parasites lack combinatorial drug targets as effective paradigms. Targeting signaling mechanisms operative in these pathogens can provide greater molecules in combatting their infections.

PBMC CDC42 reveals the disease activity and treatment efficacy of TNF inhibitor in patients with ankylosing spondylitis

OBJECTIVE

Cell division cycle 42 (CDC42) regulates the polarization of M2 macrophage and maintains the T cell homeostasis, to participate in multiple autoimmune diseases, while its clinical involvement in ankylosing spondylitis (AS) remains unclear. Hence, the current study aimed to investigate the correlation of CDC42 with clinical characteristics and treatment outcome in AS patients receiving tumor necrosis factor (TNF) inhibitor therapy.

METHODS

Peripheral blood mononuclear cell (PBMC) CDC42 expression was detected at baseline, week (W) 4, W8, and W12 after TNF inhibitor treatment in 91 AS patients and in 50 HCs after enrollment. Furthermore, serum TNF-α, interferon-γ (IFN-γ), interleukin-10 (IL-10), and interleukin-17A (IL-17A) from AS patients were detected at baseline.

RESULTS

Blood CDC42 was lower in AS patients compared with HCs (p < 0.001). Additionally, blood CDC42 was negatively linked with CRP (r = -0.349, p = 0.001), BASDAI score (r = -0.243, p = 0.020), and ASDAS_CRP score (r = -0.238, p = 0.023) in AS patients; however, blood CDC42 was not correlated with other clinical characteristics. Besides, CDC42 was negatively correlated with TNF-α (r = -0.237, p = 0.024) and IL-17A (r = -0.339, p = 0.001) but not with IFN-γ (p = 0.083) or IL-10 (p = 0.280). Moreover, blood CDC42 was elevated after TNF inhibitor treatment (p < 0.001). Meanwhile, blood CDC42 was not varied at baseline and W4 between response patients and non-response patients, while it was higher at W8 (p = 0.019) and W12 (p = 0.002) in response patients than in non-response patients after treatment.

CONCLUSION

Blood CDC42 deficiency links with elevated pro-inflammatory cytokines, disease activity and unsatisfying response to TNF inhibitor in AS patients.

Rho GTPase gene expression and breast cancer risk: a Mendelian randomization analysis

The Rho GTPase family consists of 20 genes encoding intracellular signalling proteins that influence cytoskeletal dynamics, cell migration and cell cycle progression. They are implicated in breast cancer progression but their role in breast cancer aetiology is unknown. As aberrant Rho GTPase activity could be associated with breast cancer, we aimed to determine the potential for a causal role of Rho GTPase gene expression in breast cancer risk, using two-sample Mendelian randomization (MR). MR was undertaken in 122,977 breast cancer cases and 105,974 controls, including 69,501 estrogen receptor positive (ER+) cases and 105,974 controls, and 21,468 ER negative (ER-) cases and 105,974 controls. Single nucleotide polymorphisms (SNPs) underlying expression quantitative trait loci (eQTLs) obtained from normal breast tissue, breast cancer tissue and blood were used as genetic instruments for Rho GTPase expression. As a sensitivity analysis, we undertook co-localisation to examine whether findings reflected shared causal variants or genomic confounding. We identified genetic instruments for 14 of the 20 human Rho GTPases. Using eQTLs obtained from normal breast tissue and normal blood, we identified evidence of a causal role of RHOD in overall and ER+ breast cancers (overall breast cancer: odds ratio (OR) per standard deviation (SD) increase in expression level 1.06; (95% confidence interval (CI) 1.03, 1.09; P = 5.65 × 10-5) and OR 1.22 (95% CI 1.11, 1.35; P = 5.22 × 10-5) in normal breast tissue and blood respectively). There was a consistent direction of association for ER- breast cancer, although the effect-estimate was imprecisely estimated. Using eQTLs from breast cancer tissue and normal blood there was some evidence that CDC42 was negatively associated with overall and ER + breast cancer risk. The evidence from colocalization analyses strongly supported our MR results particularly for RHOD. Our study suggests a potential causal role of increased RHOD gene expression, and, although the evidence is weaker, a potential protective role for CDC42 gene expression, in overall and ER+ breast cancers. These finding warrant validation in independent samples and further biological investigation to assess whether they may be suitable targets for drug targeting.

Homer signaling pathways as effective therapeutic targets for ischemic and traumatic brain injuries and retinal lesions

Ischemic and traumatic insults to the central nervous system account for most serious acute and fatal brain injuries and are usually characterized by primary and secondary damage. Secondary damage presents the greatest challenge for medical staff; however, there are currently few effective therapeutic targets for secondary damage. Homer proteins are postsynaptic scaffolding proteins that have been implicated in ischemic and traumatic insults to the central nervous system. Homer signaling can exert either positive or negative effects during such insults, depending on the specific subtype of Homer protein. Homer 1b/c couples with other proteins to form postsynaptic densities, which form the basis of synaptic transmission, while Homer1a expression can be induced by harmful external factors. Homer 1c is used as a unique biomarker to reveal alterations in synaptic connectivity before and during the early stages of apoptosis in retinal ganglion cells, mediated or affected by extracellular or intracellular signaling or cytoskeletal processes. This review summarizes the structural features, related signaling pathways, and diverse roles of Homer proteins in physiological and pathological processes. Upregulating Homer1a or downregulating Homer1b/c may play a neuroprotective role in secondary brain injuries. Homer also plays an important role in the formation of photoreceptor synapses. These findings confirm the neuroprotective effects of Homer, and support the future design of therapeutic drug targets or gene therapies for ischemic and traumatic brain injuries and retinal disorders based on Homer proteins.

The relationship of blood CDC42 level with Th1 cells, Th17 cells, inflammation markers, disease risk/activity, and treatment efficacy of rheumatoid arthritis

BACKGROUND

Cell division control protein 42 (CDC42) is reported to be involved in multiple inflammation processes by regulating T cell differentiation, maintaining immune cell homeostasis, and altering their function, while no relevant studies explored its clinical role in patients with rheumatoid arthritis (RA). Therefore, this study aimed to explore the correlation of CDC42 with Th1 and Th17 cells and its association with disease risk, activity, and treatment outcomes of RA.

METHODS

After the enrollment of 95 active RA patients and 50 healthy subjects (HC), their CDC42, Th1 cells, and Th17 cells were assayed by RT-qPCR and flow cytometry, accordingly. For RA patients only, CDC42 was also detected at W6, and W12 after treatment. The treatment response and remission status were evaluated at W12.

RESULTS

Compared to HC, CDC42 was reduced (P < 0.001), while Th1 cells (P = 0.021) and Th17 cells (P < 0.001) were increased in RA patients. Besides, CDC42 was negatively correlated with Th17 cells (P < 0.001), erythrocyte sedimentation rate (ESR) (P = 0.012), C-reactive protein (P = 0.002), and disease activity score in 28 joints (DAS28) (P = 0.007), but did not relate to Th1 cells or other disease features (all P > 0.05) in RA patients. Furthermore, CDC42 was elevated during treatment in RA patients (P < 0.001). Moreover, CDC42 increment at W12 correlated with treatment response (P = 0.004). Besides, CDC42 elevation at W0 (P = 0.038), W6 (P = 0.001), and W12 (P < 0.001) also linked with treatment remission.

CONCLUSION

CDC42 has the potential to serve as a biomarker to monitor disease activity and treatment efficacy in patients with RA.

Cdc42 in osterix-expressing cells alters osteoblast behavior and myeloid lineage commitment

Osteoblasts are not only responsible for bone formation. They also support hematopoiesis. This requires responding to cues originating from several signaling pathways, a task performed by Rho GTPases. We therefore examined several transgenic mouse models and used inhibitors of Cdc42 in vitro. Deletion of Cdc42 in vivo using the Osterix promoter suppressed osteoblast function, while its deletion in differentiating osteoblasts using the Collagen-α1(I) promoter decreased osteoblast numbers. In both cases, bone mineral density diminished confirming the importance of Cdc42. Evaluation of hematopoiesis revealed that deletion of Cdc42 using the Osterix, but not the Collagen-α1(I) promoter increased the common myeloid progenitors (CMPs) in the bone marrow as well as the erythrocytes and the thrombocytes/platelets in peripheral blood. Causality between Cdc42 loss in early osteoblasts and increased myelopoiesis was confirmed in vitro. Work in vitro supported the conclusion that interleukin-4 mediated the increase in myelopoiesis. Thus, Cdc42 is required for healthy bone through regulation of bone formation in Osterix-expressing osteoblasts and the number of osteoblasts in differentiating osteoblasts. In addition, its expression in early osteoblasts/stromal cells modulates myelopoiesis. This highlights the importance of osteoblasts in regulating hematopoiesis.

Rac1 promotes kidney collecting duct integrity by limiting actomyosin activity

A polarized collecting duct (CD), formed from the branching ureteric bud (UB), is a prerequisite for an intact kidney. The small Rho GTPase Rac1 is critical for actin cytoskeletal regulation. We investigated the role of Rac1 in the kidney collecting system by selectively deleting it in mice at the initiation of UB development. The mice exhibited only a mild developmental phenotype; however, with aging, the CD developed a disruption of epithelial integrity and function. Despite intact integrin signaling, Rac1-null CD cells had profound adhesion and polarity abnormalities that were independent of the major downstream Rac1 effector, Pak1. These cells did however have a defect in the WAVE2–Arp2/3 actin nucleation and polymerization apparatus, resulting in actomyosin hyperactivity. The epithelial defects were reversible with direct myosin II inhibition. Furthermore, Rac1 controlled lateral membrane height and overall epithelial morphology by maintaining lateral F-actin and restricting actomyosin. Thus, Rac1 promotes CD epithelial integrity and morphology by restricting actomyosin via Arp2/3-dependent cytoskeletal branching.

Born to Run? Diverse Modes of Epithelial Migration

Bundled with various kinds of adhesion molecules and anchored to the basement membrane, the epithelium has historically been considered as an immotile tissue and, to migrate, it first needs to undergo epithelial-mesenchymal transition (EMT). Since its initial description more than half a century ago, the EMT process has fascinated generations of developmental biologists and, more recently, cancer biologists as it is believed to be essential for not only embryonic development, organ formation, but cancer metastasis. However, recent progress shows that epithelium is much more motile than previously realized. Here, we examine the emerging themes in epithelial collective migration and how this has impacted our understanding of EMT.

FCHSD2 cooperates with CDC42 and N-WASP to regulate cell protrusion formation

Actin-based, finger-like cell protrusions such as microvilli and filopodia play important roles in epithelial cells. Several proteins have been identified to regulate cell protrusion formation, which helps us to learn about the underlying mechanism of this process. FCH domain and double SH3 domains containing protein 2 (FCHSD2) belongs to the FCH and Bin-Amphiphysin-Rvs (F-BAR) protein family, containing an N-terminal F-BAR domain, two SH3 domains, and a C-terminal PDZ domain-binding interface (PBI). Previously, we found that FCHSD2 interacts with WASP/N-WASP and stimulates ARP2/3-mediated actin polymerization in vitro. In the present work, we show that FCHSD2 promotes the formation of apical and lateral cell protrusions in cultured cells. Our data suggest that FCHSD2 cooperates with CDC42 and N-WASP in regulating apical cell protrusion formation. In line with this, biochemical studies reveal that FCHSD2 and CDC42 simultaneously bind to N-WASP, forming a protein complex. Interestingly, the F-BAR domain of FCHSD2 induces lateral cell protrusion formation independently of N-WASP. Furthermore, we show that the ability of FCHSD2 to induce cell protrusion formation requires its plasma membrane-binding ability. In summary, our present work suggests that FCHSD2 cooperates with CDC42 and N-WASP to regulate cell protrusion formation in a membrane-dependent manner.

Macrothrombocytopenia of Takenouchi-Kosaki syndrome is ameliorated by CDC42 specific- and lipidation inhibitors in MEG-01 cells

Macrothrombocytopenia is a common pathology of missense mutations in genes regulating actin dynamics. Takenouchi-Kosaki syndrome (TKS) harboring the c.191A > G, Tyr64Cys (Y64C) variant in Cdc42 exhibits a variety of clinical manifestations, including immunological and hematological anomalies. In the present study, we investigated the functional abnormalities of the Y64C mutant in HEK293 cells and elucidated the mechanism of macrothrombocytopenia, one of the symptoms of TKS patients, by monitoring the production of platelet-like particles (PLP) using MEG-01 cells. We found that the Y64C mutant was concentrated at the membrane compartment due to impaired binding to Rho-GDI and more active than the wild-type. The Y64C mutant also had lower association with its effectors Pak1/2 and N-WASP. Y64C mutant-expressing MEG-01 cells demonstrated short cytoplasmic protrusions with aberrant F-actin and microtubules, and reduced PLP production. This suggested that the Y64C mutant facilitates its activity and membrane localization, resulting in impaired F-actin dynamics for proplatelet extension, which is necessary for platelet production. Furthermore, such dysfunction was ameliorated by either suppression of Cdc42 activity or prenylation using chemical inhibitors. Our study may lead to pharmacological treatments for TKS patients.

Proximity proteomics identifies PAK4 as a component of Afadin-Nectin junctions

Human PAK4 is an ubiquitously expressed p21-activated kinase which acts downstream of Cdc42. Since PAK4 is enriched in cell-cell junctions, we probed the local protein environment around the kinase with a view to understanding its location and substrates. We report that U2OS cells expressing PAK4-BirA-GFP identify a subset of 27 PAK4-proximal proteins that are primarily cell-cell junction components. Afadin/AF6 showed the highest relative biotin labelling and links to the nectin family of homophilic junctional proteins. Reciprocally >50% of the PAK4-proximal proteins were identified by Afadin BioID. Co-precipitation experiments failed to identify junctional proteins, emphasizing the advantage of the BioID method. Mechanistically PAK4 depended on Afadin for its junctional localization, which is similar to the situation in Drosophila. A highly ranked PAK4-proximal protein LZTS2 was immuno-localized with Afadin at cell-cell junctions. Though PAK4 and Cdc42 are junctional, BioID analysis did not yield conventional cadherins, indicating their spatial segregation. To identify cellular PAK4 substrates we then assessed rapid changes (12') in phospho-proteome after treatment with two PAK inhibitors. Among the PAK4-proximal junctional proteins seventeen PAK4 sites were identified. We anticipate mammalian group II PAKs are selective for the Afadin/nectin sub-compartment, with a demonstrably distinct localization from tight and cadherin junctions.

Pak1 and PP2A antagonize aPKC function to support cortical tension induced by the Crumbs-Yurt complex

The Drosophila polarity protein Crumbs is essential for the establishment and growth of the apical domain in epithelial cells. The protein Yurt limits the ability of Crumbs to promote apical membrane growth, thereby defining proper apical/lateral membrane ratio that is crucial for forming and maintaining complex epithelial structures such as tubes or acini. Here, we show that Yurt also increases Myosin-dependent cortical tension downstream of Crumbs. Yurt overexpression thus induces apical constriction in epithelial cells. The kinase aPKC phosphorylates Yurt, thereby dislodging the latter from the apical domain and releasing apical tension. In contrast, the kinase Pak1 promotes Yurt dephosphorylation through activation of the phosphatase PP2A. The Pak1–PP2A module thus opposes aPKC function and supports Yurt-induced apical constriction. Hence, the complex interplay between Yurt, aPKC, Pak1, and PP2A contributes to the functional plasticity of Crumbs. Overall, our data increase our understanding of how proteins sustaining epithelial cell polarization and Myosin-dependent cell contractility interact with one another to control epithelial tissue architecture.

Regulation of the Actin Cytoskeleton via Rho GTPase Signalling in Dictyostelium and Mammalian Cells: A Parallel Slalom

Both Dictyostelium amoebae and mammalian cells are endowed with an elaborate actin cytoskeleton that enables them to perform a multitude of tasks essential for survival. Although these organisms diverged more than a billion years ago, their cells share the capability of chemotactic migration, large-scale endocytosis, binary division effected by actomyosin contraction, and various types of adhesions to other cells and to the extracellular environment. The composition and dynamics of the transient actin-based structures that are engaged in these processes are also astonishingly similar in these evolutionary distant organisms. The question arises whether this remarkable resemblance in the cellular motility hardware is accompanied by a similar correspondence in matching software, the signalling networks that govern the assembly of the actin cytoskeleton. Small GTPases from the Rho family play pivotal roles in the control of the actin cytoskeleton dynamics. Indicatively, Dictyostelium matches mammals in the number of these proteins. We give an overview of the Rho signalling pathways that regulate the actin dynamics in Dictyostelium and compare them with similar signalling networks in mammals. We also provide a phylogeny of Rho GTPases in Amoebozoa, which shows a variability of the Rho inventories across different clades found also in Metazoa.

Apical PAR complex proteins protect against programmed epithelial assaults to create a continuous and functional intestinal lumen

Sustained polarity and adhesion of epithelial cells is essential for the protection of our organs and bodies, and this epithelial integrity emerges during organ development amidst numerous programmed morphogenetic assaults. Using the developing Caenorhabditis elegans intestine as an in vivo model, we investigated how epithelia maintain their integrity through cell division and elongation to build a functional tube. Live imaging revealed that apical PAR complex proteins PAR-6/Par6 and PKC-3/aPkc remained apical during mitosis while apical microtubules and microtubule-organizing center (MTOC) proteins were transiently removed. Intestine-specific depletion of PAR-6, PKC-3, and the aPkc regulator CDC-42/Cdc42 caused persistent gaps in the apical MTOC as well as in other apical and junctional proteins after cell division and in non-dividing cells that elongated. Upon hatching, gaps coincided with luminal constrictions that blocked food, and larvae arrested and died. Thus, the apical PAR complex maintains apical and junctional continuity to construct a functional intestinal tube.

Constitutive activation of β-catenin in odontoblasts induces aberrant pulp calcification in mouse incisors

During dentin formation, odontoblast polarization ensures that odontoblasts directionally secrete dentin matrix protein, leading to tubular dentin formation; however, little is known about the major features and regulatory mechanisms of odontoblast polarization. In a study of epithelial cell polarization, β-catenin was shown to serve as a structural component of cadherin-based adherens junctions to initiate cell polarity. However, the role of β-catenin in odontoblast polarization has not been well investigated. In this study, we explored whether β-catenin participated in odontoblast polarization to regulate the secretion of mineralization proteins. We established Col1-CreErt2; β-catenin exon3fl/fl (CA-β-catenin) mice, which constitutively activate β-catenin in odontoblasts. CA-β-catenin mice exhibited disorganization and depolarization of incisor odontoblasts. Moreover, the incisor dentin was hypomineralized, and ectopic calcification was found in mouse incisor pulp. In addition, by constitutive activation of β-catenin, the expression levels of the core polarity molecule Cdc42 and its downstream polarity protein complex Par3-Par6-aPKC were decreased in the incisors of CA-β-catenin mice. These findings suggest that β-catenin plays an essential role in dentin formation by regulating odontoblast polarization.

Congenital biliary atresia is correlated with disrupted cell junctions and polarity caused by Cdc42 insufficiency in the liver

Rationale: Congenital biliary atresia (BA) is a destructive obliterative cholangiopathy of neonates that affects both intrahepatic and extrahepatic bile ducts. However, the cause of BA is largely unknown.

Methods: We explored the cell junctions and polarity complexes in early biopsy BA livers by immunofluorescence staining and western blot. Cdc42, as a key cell junction and polarity regulator, was found dramatically decreased in BA livers. Therefore, in order to investigate the role of Cdc42 in BA development, we constructed liver-specific and tamoxifen induced cholangiocyte-specific Cdc42 deleted transgenic mice. We further evaluated the role of bile acid in aggravating biliary damage in Cdc42 insufficient mouse liver.

Results: We found a dramatic defect in the assembly of cell junctions and polarity complexes in both cholangiocytes and hepatocytes in BA livers. This defect was characterized by the disordered location of cell junction proteins, including ZO1, β-catenin, E-cadherin and claudin-3. Cdc42 and its active form, Cdc42-GTP, which serves as a small Rho GTPase to orchestrate the assembly of polarity complexes with Par6/Par3/αPKC, were substantially reduced in BA livers. Selective Cdc42 deficiency in fetal mouse cholangiocytes resulted in histological changes similar to those found in human BA livers, including obstruction in both the intra- and extrahepatic bile ducts, epithelial atrophy, and the disruption of cell junction and polarity complexes. A reduction in bile acids notably improved the histology and serological indices in Cdc42-mutant mice.

Conclusion: Our results illustrate that BA is closely correlated with the impaired assembly of cell junction and polarity complexes in liver cells, which is likely caused by Cdc42 insufficiency and aggravated by bile acid corrosion.

Helicobacter pylori-induced gastric cancer is orchestrated by MRCKβ-mediated Siah2 phosphorylation

BACKGROUND

Helicobacter pylori-mediated gastric carcinogenesis is initiated by a plethora of signaling events in the infected gastric epithelial cells (GECs). The E3 ubiquitin ligase seven in absentia homolog 2 (Siah2) is induced in GECs in response to H. pylori infection. Posttranslational modifications of Siah2 orchestrate its function as well as stability. The aim of this study was to evaluate Siah2 phosphorylation status under the influence of H. pylori infection and its impact in gastric cancer progression.

METHODS

H. pylori-infected various GECs, gastric tissues from H. pylori-infected GC patients and H. felis-infected C57BL/6 mice were evaluated for Siah2 phosphorylation by western blotting or immunofluorescence microscopy. Coimmunoprecipitation assay followed by mass spectrometry were performed to identify the kinases interacting with Siah2. Phosphorylation sites of Siah2 were identified by using various plasmid constructs generated by site-directed mutagenesis. Proteasome inhibitor MG132 was used to investigate proteasome degradation events. The importance of Siah2 phosphorylation on tumorigenicity of infected cells were detected by using phosphorylation-null mutant and wild type Siah2 stably-transfected cells followed by clonogenicity assay, cell proliferation assay, anchorage-independent growth and transwell invasion assay.

RESULTS

Siah2 was phosphorylated in H. pylori-infected GECs as well as in metastatic GC tissues at residues serine⁶ (Ser⁶) and threonine²⁷⁹ (Thr²⁷⁹). Phosphorylation of Siah2 was mediated by MRCKβ, a Ser/Thr protein kinase. MRCKβ was consistently expressed in uninfected GECs and noncancer gastric tissues but its level decreased in infected GECs as well as in metastatic tissues which had enhanced Siah2 expression. Infected murine gastric tissues showed similar results. MRCKβ could phosphorylate Siah2 but itself got ubiquitinated from this interaction leading to the proteasomal degradation of MRCKβ and use of proteasomal inhibitor MG132 could rescue MRCKβ from Siah2-mediated degradation. Ser⁶ and Thr²⁷⁹ phosphorylated-Siah2 was more stable and tumorigenic than its non-phosphorylated counterpart as revealed by the proliferation, invasion, migration abilities and anchorage-independent growth of stable-transfected cells.

CONCLUSIONS

Increased level of Ser⁶ and Thr²⁷⁹-phosphorylated-Siah2 and downregulated MRCKβ were prominent histological characteristics of Helicobacter-infected gastric epithelium and metastatic human GC. MRCKβ-dependent Siah2 phosphorylation stabilized Siah2 which promoted anchorage-independent survival and proliferative potential of GECs. Phospho-null mutants of Siah2 (S6A and T279A) showed abated tumorigenicity.

Collective Polarization of Cancer Cells at the Monolayer Boundary

Cell polarization, a process depending on both intracellular and intercellular interactions, is crucial for collective cell migration that commonly emerges in embryonic development, tissue morphogenesis, wound healing and cancer metastasis. Although invasive cancer cells display weak cell-cell interactions, they can invade host tissues through a collective mode. Yet, how cancer cells without stable cell-cell junctions polarize collectively to migrate and invade is not fully understood. Here, using a wound-healing assay, we elucidate the polarization of carcinoma cells at the population level. We show that with loose intercellular connections, the highly polarized leader cells can induce the polarization of following cancer cells and subsequent transmission of polarity information by membrane protrusions, leading to gradient polarization at the monolayer boundary. Unlike the polarization of epithelial monolayer where Rac1/Cdc42 pathway functions primarily, our data show that collective polarization of carcinoma cells is predominantly controlled by Golgi apparatus, a disruption of which results in the destruction of collective polarization over a large scale. We reveal that the Golgi apparatus can sustain membrane protrusion formation, polarized secretion, intracellular trafficking, and F-actin polarization, which contribute to collective cancer cell polarization and its transmission between cells. These findings could advance our understanding of collective cancer invasion in tumors.

Tuba Activates Cdc42 during Neuronal Polarization Downstream of the Small GTPase Rab8a

The acquisition of neuronal polarity is a complex molecular process that depends on changes in cytoskeletal dynamics and directed membrane traffic, regulated by the Rho and Rab families of small GTPases, respectively. However, during axon specification, a molecular link that couples these protein families has yet to be identified. In this paper, we describe a new positive feedback loop between Rab8a and Cdc42, coupled by Tuba, a Cdc42-specific guanine nucleotide-exchange factor (GEF), that ensures a single axon generation in rodent hippocampal neurons from embryos of either sex. Accordingly, Rab8a or Tuba gain-of-function generates neurons with supernumerary axons whereas Rab8a or Tuba loss-of-function abrogated axon specification, phenocopying the well-established effect of Cdc42 on neuronal polarity. Although Rab8 and Tuba do not interact physically, the activity of Rab8 is essential to generate a proximal to distal axonal gradient of Tuba in cultured neurons. Tuba-associated and Rab8a-associated polarity defects are also evidenced in vivo, since dominant negative (DN) Rab8a or Tuba knock-down impairs cortical neuronal migration in mice. Our results suggest that Tuba coordinates directed vesicular traffic and cytoskeleton dynamics during neuronal polarization.SIGNIFICANCE STATEMENT The morphologic, biochemical, and functional differences observed between axon and dendrites, require dramatic structural changes. The extension of an axon that is 1 µm in diameter and grows at rates of up to 500 µm/d, demands the confluence of two cellular processes: directed membrane traffic and fine-tuned cytoskeletal dynamics. In this study, we show that both processes are integrated in a positive feedback loop, mediated by the guanine nucleotide-exchange factor (GEF) Tuba. Tuba connects the activities of the Rab GTPase Rab8a and the Rho GTPase Cdc42, ensuring the generation of a single axon in cultured hippocampal neurons and controlling the migration of cortical neurons in the developing brain. Finally, we provide compelling evidence that Tuba is the GEF that mediates Cdc42 activation during the development of neuronal polarity.

Active and Inactive Cdc42 Differ in Their Insert Region Conformational Dynamics

Cell division control protein 42 homolog (Cdc42) protein, a Ras superfamily GTPase, regulates cellular activities, including cancer progression. Using all-atom molecular dynamics (MD) simulations and essential dynamic analysis, we investigated the structure and dynamics of the catalytic domains of GDP-bound (inactive) and GTP-bound (active) Cdc42 in solution. We discovered substantial differences in the dynamics of the inactive and active forms, particularly in the "insert region" (residues 122-135), which plays a role in Cdc42 activation and binding to effectors. The insert region has larger conformational flexibility in the GDP-bound Cdc42 than in the GTP-bound Cdc42. The G2 loop and switch I at the effector lobe of the catalytic domain exhibit large conformational changes in both the GDP- and the GTP-bound systems, but in the GTP-bound Cdc42, the switch I interactions with GTP are retained. Oncogenic mutations were identified in the Ras superfamily. In Cdc42, the G12V and Q61L mutations decrease the GTPase activity. We simulated these mutations in both GDP- and GTP-bound Cdc42. Although the overall structural organization is quite similar between the wild type and the mutants, there are small differences in the conformational dynamics, especially in the two switch regions. Taken together, the G12V and Q61L mutations may play a role similar to their K-Ras counterparts in nucleotide binding and activation. The conformational differences, which are mainly in the insert region and, to a lesser extent, in the switch regions flanking the nucleotide binding site, can shed light on binding and activation. We propose that the differences are due to a network of hydrogen bonds that gets disrupted when Cdc42 is bound to GDP, a disruption that does not exist in other Rho GTPases. The differences in the dynamics between the two Cdc42 states suggest that the inactive conformation has reduced ability to bind to effectors.