An essential role for Rho, Rac, and Cdc42 GTPases in cell cycle progression through G1

A transcribed ultraconserved noncoding RNA, uc.285+, promotes colorectal cancer proliferation through dual targeting of CDC42 by directly binding mRNA and protein

The transcribed ultraconserved region (T-UCR) belongs to a new type of lncRNAs that are conserved in homologous regions of the rat, mouse and human genomes. A lot of research has reported that differential expression of T-UCRs can influence the development of various cancers, revealing the ability of T-UCRs as new therapeutic targets or potential cancer biomarkers. Most studies on the molecular mechanisms of T-UCRs in cancer have focused on ceRNA regulatory networks and interactions with target proteins, but the present study reveals an innovative dual-targeted regulatory approach in which T-UCRs bind directly to mRNAs and directly to proteins. We screened T-UCRs that may be related to colorectal cancer (CRC) by performing a whole-genome T-UCR gene microarray and further studied the functional mechanism of T-UCR uc.285+ in the development of CRC. Modulation of uc.285+ affected the proliferation of CRC cell lines and influenced the expression of the CDC42 gene. We also found that uc.285+ promoted the proliferation of CRC cells by directly binding to CDC42 mRNA and enhancing its stability while directly binding to CDC42 protein and affecting its stability. In short, our research on the characteristics of cell proliferation found that uc.285+ has a biological function in promoting CRC proliferation. uc.285+ may have considerable potential as a new diagnostic biomarker for CRC.

Dual inhibition of P38 MAPK and JNK pathways preserves stemness markers and alleviates premature activation of muscle stem cells during isolation

BACKGROUND

Adult skeletal muscle contains resident muscle stem cells (MuSC) with high myogenic and engraftment potentials, making them suitable for cell therapy and regenerative medicine approaches. However, purification process of MuSC remains a major hurdle to their use in the clinic. Indeed, muscle tissue enzymatic dissociation triggers a massive activation of stress signaling pathways, among which P38 and JNK MAPK, associated with a premature loss of MuSC quiescence. While the role of these pathways in the myogenic progression of MuSC is well established, the extent to which their dissociation-induced activation affects the functionality of these cells remains unexplored.

METHODS

We assessed the effect of P38 and JNK MAPK induction on stemness marker expression and MuSC activation state during isolation by pharmacological approaches. MuSC functionality was evaluated by in vitro assays and in vivo transplantation experiments. We performed a comparative analysis of the transcriptome of human MuSC purified with pharmacological inhibitors of P38 and JNK MAPK (SB202190 and SP600125, respectively) versus available RNAseq resources.

RESULTS

We monitored PAX7 protein levels in murine MuSC during muscle dissociation and demonstrated a two-step decline partly dependent on P38 and JNK MAPK activities. We showed that simultaneous inhibition of these pathways throughout the MuSC isolation process preserves the expression of stemness markers and limits their premature activation, leading to improved survival and amplification in vitro as well as increased engraftment in vivo. Through a comparative RNAseq analysis of freshly isolated human MuSC, we provide evidence that our findings in murine MuSC could be relevant to human MuSC. Based on these findings, we implemented a purification strategy, significantly improving the recovery yields of human MuSC.

CONCLUSION

Our study highlights the pharmacological limitation of P38 and JNK MAPK activities as a suitable strategy to qualitatively and quantitatively ameliorate human MuSC purification process, which could be of great interest for cell-based therapies.

The Wingless planar cell polarity pathway is essential for optimal activity-dependent synaptic plasticity

From fly to man, the Wingless (Wg)/Wnt signaling molecule is essential for both the stability and plasticity of the nervous system. The Drosophila neuromuscular junction (NMJ) has proven to be a useful system for deciphering the role of Wg in directing activity-dependent synaptic plasticity (ADSP), which, in the motoneuron, has been shown to be dependent on both the canonical and the noncanonical calcium Wg pathways. Here we show that the noncanonical planar cell polarity (PCP) pathway is an essential component of the Wg signaling system controlling plasticity at the motoneuron synapse. We present evidence that disturbing the PCP pathway leads to a perturbation in ADSP. We first show that a PCP-specific allele of disheveled (dsh) affects the de novo synaptic structures produced during ADSP. We then show that the Rho GTPases downstream of Dsh in the PCP pathway are also involved in regulating the morphological changes that take place after repeated stimulation. Finally, we show that Jun kinase is essential for this phenomenon, whereas we found no indication of the involvement of the transcription factor complex AP1 (Jun/Fos). This work shows the involvement of the neuronal PCP signaling pathway in supporting ADSP. Because we find that AP1 mutants can perform ADSP adequately, we hypothesize that, upon Wg activation, the Rho GTPases and Jun kinase are involved locally at the synapse, in instructing cytoskeletal dynamics responsible for the appearance of the morphological changes occurring during ADSP.

The role of fibronectin in mediating cell migration

Fibronectin (FN) is a major extracellular matrix (ECM) protein involved in a wide range of physiological processes, including cell migration. These FN-mediated cell migration events are essential to processes such as wound repair, cancer metastasis, and vertebrate development. This review synthesizes mainly current literature to provide an overview of the mechanoregulatory role of FN-mediated cell migration. Background on FN structure and role in mechanotransduction is provided. Cell migration concepts are introduced, including the general cell migration mechanism and classification of cell migration types. Then, FN-mediated events that directly affect cell migration are explored. Finally, a focus on FN in tissue repair and cancer migration is presented, as these topics represent a large amount of current research.

Functional Conservation of the Small GTPase Rho5/Rac1-A Tale of Yeast and Men

Small GTPases are molecular switches that participate in many essential cellular processes. Amongst them, human Rac1 was first described for its role in regulating actin cytoskeleton dynamics and cell migration, with a close relation to carcinogenesis. More recently, the role of Rac1 in regulating the production of reactive oxygen species (ROS), both as a subunit of NADPH oxidase complexes and through its association with mitochondrial functions, has drawn attention. Malfunctions in this context affect cellular plasticity and apoptosis, related to neurodegenerative diseases and diabetes. Some of these features of Rac1 are conserved in its yeast homologue Rho5. Here, we review the structural and functional similarities and differences between these two evolutionary distant proteins and propose yeast as a useful model and a device for high-throughput screens for specific drugs.

A preliminary study of the miRNA restitution effect on CNV-induced miRNA downregulation in CAKUT

BACKGROUND

The majority of CAKUT-associated CNVs overlap at least one miRNA gene, thus affecting the cellular levels of the corresponding miRNA. We aimed to investigate the potency of restitution of CNV-affected miRNA levels to remediate the dysregulated expression of target genes involved in kidney physiology and development in vitro.

METHODS

Heterozygous MIR484 knockout HEK293 and homozygous MIR185 knockout HEK293 cell lines were used as models depicting the deletion of the frequently affected miRNA genes by CAKUT-associated CNVs. After treatment with the corresponding miRNA mimics, the levels of the target genes have been compared to the non-targeting control treatment. For both investigated miRNAs, MDM2 and PKD1 were evaluated as common targets, while additional 3 genes were investigated as targets of each individual miRNA (NOTCH3, FIS1 and APAF1 as hsa-miR-484 targets and RHOA, ATF6 and CDC42 as hsa-miR-185-5p targets).

RESULTS

Restitution of the corresponding miRNA levels in both knockout cell lines has induced a change in the mRNA levels of certain candidate target genes, thus confirming the potential to alleviate the CNV effect on miRNA expression. Intriguingly, HEK293 WT treatment with investigated miRNA mimics has triggered a more pronounced effect, thus suggesting the importance of miRNA interplay in different genomic contexts.

CONCLUSIONS

Dysregulation of multiple mRNA targets mediated by CNV-affected miRNAs could represent the underlying mechanism behind the unresolved CAKUT occurrence and phenotypic variability observed in CAKUT patients. Characterizing miRNAs located in CNVs and their potential to become molecular targets could eventually help in understanding and improving the management of CAKUT.

Human Parathyroid Hormone (1-34) accelerates skin wound healing through inducing cell migration via up-regulating the expression of Rac1

Delayed wound healing is a public issue that imposes a significant burden on both society and the patients themselves. To date, although numerous methods have been developed to accelerate the speed of wound closure, the therapeutic effects are partially limited due to the complex procedures, high costs, potential side effects, and ethical concerns. While some studies have reported that the in-vivo application of Human Parathyroid Hormone (1-34) (hPTH(1-34)) promotes the wound-healing process, the definitive role and underlying mechanisms through which it regulates the behavior of fibroblasts and keratinocytes remains unclear. Herein, hPTH(1-34)'s role in cell migration is evaluated with a series of in-vitro and in-vivo studies, whereby hPTH(1-34)'s underlying mechanism in activating the two types of cells was detected. The in-vitro study revealed that hPTH(1-34) enhanced the migration of both fibroblasts and HaCaT cells. Ras-associated C3 botulinum toxin subunit 1 (Rac1), a classical member of the Rho family, was upregulated in hPTH(1-34)-treated fibroblasts and HaCaT cells. Further study by silencing the expression of Rac1 with siRNA reversed the hPTH(1-34)-enhanced cell migration, thus confirming that Rac1 was involved in hPTH(1-34)-induced cell behavior. In-vivo study on rat wound models confirmed the effects of hPTH(1-34) on fibroblasts and keratinocytes, with increased collagen deposition, fibroblasts accumulation, and Rac1 expression in the hPTH(1-34)-treated wounds. In summary, the present study demonstrated that hPTH(1-34) accelerated wound healing through enhancing the migration of cells through the up-regulation of Rac1 expression.

Thrombospondin 1 and Reelin act through Vldlr to regulate cardiac growth and repair

Adult mammalian cardiomyocytes have minimal cell cycle capacity, which leads to poor regeneration after cardiac injury such as myocardial infarction. Many positive regulators of cardiomyocyte cell cycle and cardioprotective signals have been identified, but extracellular signals that suppress cardiomyocyte proliferation are poorly understood. We profiled receptors enriched in postnatal cardiomyocytes, and found that very-low-density-lipoprotein receptor (Vldlr) inhibits neonatal cardiomyocyte cell cycle. Paradoxically, Reelin, the well-known Vldlr ligand, expressed in cardiac Schwann cells and lymphatic endothelial cells, promotes neonatal cardiomyocyte proliferation. Thrombospondin1 (TSP-1), another ligand of Vldlr highly expressed in adult heart, was then found to inhibit cardiomyocyte proliferation through Vldlr, and may contribute to Vldlr's overall repression on proliferation. Mechanistically, Rac1 and subsequent Yap phosphorylation and nucleus translocation mediate the regulation of the cardiomyocyte cell cycle by TSP-1/Reelin-Vldlr signaling. Importantly, Reln mutant neonatal mice displayed impaired cardiomyocyte proliferation and cardiac regeneration after apical resection, while cardiac-specific Thbs1 deletion and cardiomyocyte-specific Vldlr deletion promote cardiomyocyte proliferation and are cardioprotective after myocardial infarction. Our results identified a novel role of Vldlr in consolidating extracellular signals to regulate cardiomyocyte cell cycle activity and survival, and the overall suppressive TSP-1-Vldlr signal may contribute to the poor cardiac repair capacity of adult mammals.

MAST4 promotes primary ciliary resorption through phosphorylation of Tctex-1

The primary cilium undergoes cell cycle-dependent assembly and disassembly. Dysregulated ciliary dynamics are associated with several pathological conditions called ciliopathies. Previous studies showed that the localization of phosphorylated Tctex-1 at Thr94 (T94) at the ciliary base critically regulates ciliary resorption by accelerating actin remodeling and ciliary pocket membrane endocytosis. Here, we show that microtubule-associated serine/threonine kinase family member 4 (MAST4) is localized at the primary cilium. Suppressing MAST4 blocks serum-induced ciliary resorption, and overexpressing MAST4 accelerates ciliary resorption. Tctex-1 binds to the kinase domain of MAST4, in which the R503 and D504 residues are key to MAST4-mediated ciliary resorption. The ciliary resorption and the ciliary base localization of phospho-(T94)Tctex-1 are blocked by the knockdown of MAST4 or the expression of the catalytic-inactive site-directed MAST4 mutants. Moreover, MAST4 is required for Cdc42 activation and Rab5-mediated periciliary membrane endocytosis during ciliary resorption. These results support that MAST4 is a novel kinase that regulates ciliary resorption by modulating the ciliary base localization of phospho-(T94)Tctex-1. MAST4 is a potential new target for treating ciliopathies causally by ciliary resorption defects.

A novel anti-apoptotic role for Cdc42/ACK-1 signaling in neurons

Neurodegenerative diseases such as amyotrophic lateral sclerosis, Alzheimer's and Parkinson's disease are caused by a progressive and aberrant destruction of neurons in the brain and spinal cord. These disorders lack effective long-term treatments that impact the underlying mechanisms of pathogenesis and as a result, existing options focus primarily on alleviating symptomology. Dysregulated programmed cell death (i.e., apoptosis) is a significant contributor to neurodegeneration, and is controlled by a number of different factors. Rho family GTPases are molecular switches with recognized importance in proper neuronal development and migration that have more recently emerged as central regulators of apoptosis and neuronal survival. Here, we investigated a role for the Rho GTPase family member, Cdc42, and its downstream effectors, in neuronal survival and apoptosis. We initially induced apoptosis in primary cultures of rat cerebellar granule neurons (CGNs) by removing both growth factor-containing serum and depolarizing potassium from the cell medium. We then utilized both chemical inhibitors and adenoviral shRNA targeted to Cdc42 to block the function of Cdc42 or its downstream effectors under either control or apoptotic conditions. Our in vitro studies demonstrate that functional inhibition of Cdc42 or its downstream effector, activated Cdc42-associated tyrosine kinase-1 (ACK-1), had no adverse effects on CGN survival under control conditions, but significantly sensitized neurons to cell death under apoptotic conditions. In conclusion, our results suggest a key pro-survival role for Cdc42/ACK-1 signaling in neurons, particularly in regulating neuronal susceptibility to pro-apoptotic stress such as that observed in neurodegenerative disorders.

ARHGAP29 is required for keratinocyte proliferation and migration

BACKGROUND

RhoA GTPase plays critical roles in actin cytoskeletal remodeling required for controlling a diverse range of cellular functions including cell proliferation, cell adhesions, migration and changes in cell shape. RhoA cycles between an active GTP-bound and an inactive GDP-bound form, a process that is regulated by guanine nucleotide exchange factors (GEFs), and GTPase-activating proteins (GAPs). ARHGAP29 is a GAP expressed in keratinocytes of the skin and is decreased in the absence of Interferon Regulator Factor 6, a critical regulator of cell proliferation and migration. However, the role for ARHGAP29 in keratinocyte biology is unknown.

RESULTS

Novel ARHGAP29 knockdown keratinocyte cell lines were generated using both CRISPR/Cas9 and shRNA technologies. Knockdown cells exhibited significant reduction of ARHGAP29 protein (50-80%) and displayed increased filamentous actin (stress fibers), phospho-myosin light chain (contractility), cell area and population doubling time. Furthermore, we found that ARHGAP29 knockdown keratinocytes displayed significant delays in scratch wound closure in both single cell and collective cell migration conditions. Particularly, our results show a reduction in path lengths, speed, directionality and persistence in keratinocytes with reduced ARHGAP29. The delay in scratch closure was rescued by both adding back ARHGAP29 or adding a ROCK inhibitor to ARHGAP29 knockdown cells.

CONCLUSIONS

These data demonstrate that ARHGAP29 is required for keratinocyte morphology, proliferation and migration mediated through the RhoA pathway.

Cntnap2-dependent molecular networks in autism spectrum disorder revealed through an integrative multi-omics analysis

Autism spectrum disorder (ASD) is a major neurodevelopmental disorder in which patients present with core symptoms of social communication impairment, restricted interest, and repetitive behaviors. Although various studies have been performed to identify ASD-related mechanisms, ASD pathology is still poorly understood. CNTNAP2 genetic variants have been found that represent ASD genetic risk factors, and disruption of Cntnap2 expression has been associated with ASD phenotypes in mice. In this study, we performed an integrative multi-omics analysis by combining quantitative proteometabolomic data obtained with Cntnap2 knockout (KO) mice with multi-omics data obtained from ASD patients and forebrain organoids to elucidate Cntnap2-dependent molecular networks in ASD. To this end, a mass spectrometry-based proteometabolomic analysis of the medial prefrontal cortex in Cntnap2 KO mice led to the identification of Cntnap2-associated molecular features, and these features were assessed in combination with multi-omics data obtained on the prefrontal cortex in ASD patients to identify bona fide ASD cellular processes. Furthermore, a reanalysis of single-cell RNA sequencing data obtained from forebrain organoids derived from patients with CNTNAP2-associated ASD revealed that the aforementioned identified ASD processes were mainly linked to excitatory neurons. On the basis of these data, we constructed Cntnap2-associated ASD network models showing mitochondrial dysfunction, axonal impairment, and synaptic activity. Our results may shed light on the Cntnap2-dependent molecular networks in ASD.

A systematic review on the effects of ROCK inhibitors on proliferation and/or differentiation in human somatic stem cells: A hypothesis that ROCK inhibitors support corneal endothelial healing via acting on the limbal stem cell niche

Rho kinase inhibitors (ROCKi) have attracted growing multidisciplinary interest, particularly in Ophthalmology where the question as to how they promote corneal endothelial healing remains unresolved. Concurrently, stem cell biology has rapidly progressed in unravelling drivers of stem cell (SC) proliferation and differentiation, where mechanical niche factors and the actin cytoskeleton are increasingly recognized as key players. There is mounting evidence from the study of the peripheral corneal endothelium that supports the likelihood of an internal limbal stem cell niche. The possibility that ROCKi stimulate the endothelial SC niche has not been addressed. Furthermore, there is currently a paucity of data that directly evaluates whether ROCKi promotes corneal endothelial healing by acting on this limbal SC niche located near the transition zone. Therefore, we performed a systematic review examining the effects ROCKi on the proliferation and differentiation of human somatic SC, to provide insight into its effects on various human SC populations. An appraisal of electronic searches of four databases identified 1 in vivo and 58 in vitro studies (36 evaluated proliferation while 53 examined differentiation). Types of SC studied included mesenchymal (n = 32), epithelial (n = 11), epidermal (n = 8), hematopoietic and other (n = 8). The ROCK 1/2 selective inhibitor Y-27632 was used in almost all studies (n = 58), while several studies evaluated ≥2 ROCKi (n = 4) including fasudil, H-1152, and KD025. ROCKi significantly influenced human somatic SC proliferation in 81% of studies (29/36) and SC differentiation in 94% of studies (50/53). The present systemic review highlights that ROCKi are influential in regulating human SC proliferation and differentiation, and provides evidence to support the hypothesis that ROCKi promotes corneal endothelial division and maintenance via acting on the inner limbal SC niche.

Rac1 deficiency impairs postnatal development of the renal papilla

Development of the renal medulla continues after birth to form mature renal papilla and obtain urine-concentrating ability. Here, we found that a small GTPase, Rac1, plays a critical role in the postnatal development of renal papilla. Mice with distal tubule-specific deletion of Rac1 reached adulthood but showed polydipsia and polyuria with an impaired ability to concentrate urine. The elongation of renal papilla that occurs in the first weeks after birth was impaired in the Rac1-deficient infants, resulting in shortening and damage of the renal papilla. Moreover, the osmoprotective signaling mediated by nuclear factor of activated T cells 5, which is a key molecule of osmotic response to osmotic stress in renal medulla, was significantly impaired in the kidneys of the Rac1-deficient infants. These results demonstrate that Rac1 plays an important role in the development of renal papilla in the postnatal period, and suggested a potential link between Rac1 and osmotic response.

The Process of Filopodia Induction during HPV Infection

Human Papillomavirus 16 (HPV16) infects mucosal and epithelial cells and has been identified as a high-risk HPV type that is an etiologic agent of human cancers. The initial infectious process, i.e., the binding of the virus particle and its entry into the host cell, has been studied extensively, although it is not fully understood. There is still a gap in understanding the steps by which the virus is able to cross the plasma membrane after receptor binding. In this study, we demonstrate that after HPV16 comes into contact with a plasma membrane receptor, there are cytoskeletal changes resulting in an increase of filopodia numbers. This increase in filopodia numbers was transient and was maintained during the first two hours after virus addition. Our data show that there is a statistically significant increase in infection when filopodia numbers are increased by the addition of drug and virus simultaneously, and a decrease in virus infection when filopodia formation is inhibited. We describe that HPV16 binding results in the activation of Cdc42 GTPase that in turn results in an increase in filopodia. siRNA directed at Cdc42 GTPase resulted in a statistically significant reduction of infection and a corresponding lack of filopodia induction.

Transcriptomic and functional studies reveal miR-431-5p as a tumour suppressor in pancreatic ductal adenocarcinoma cells

The lactate receptor HCAR1 (hydroxycarboxylic acid receptor 1) is highly expressed in pancreatic ductal adenocarcinoma (PDAC), where it regulates lactate transport between the cancer cells. Little is known about the underlying cause of high HCAR1 expression in PDAC, and in the present study, we investigated whether HCAR1 could be a target of miRNA regulation. By searching for predicted miRNA candidates in silico, we identified miR-431-5p as a possible regulator of HCAR1. We found miR-431-5p to repress HCAR1 expression through direct binding to the 3' UTR. The endogenous expression of miR-431-5p and HCAR1 was found to be negatively related in the PDAC cell lines BxPC-3, Capan-2, and PANC-1. Overexpression of miR-431-5p inhibited cell proliferation in all the cell lines, and a shift in cell cycle progression and induction of apoptosis were found in the BxPC-3 cells. Transcriptomic analysis of mRNA from BxPC-3 cells revealed numerous differentially expressed genes (DEGs), including HCAR1, in response to miR-431-5p overexpression. A significant proportion of these DEGs was enriched in cancer-related processes and signalling pathways. Among the most significantly repressed DEGs was ATP6V0E1, encoding the integral subunit e of vacuolar ATPase (V-ATPase), an enzyme that is important for cancer cell survival. Small interfering RNA (siRNA)-mediated knockdown of HCAR1 and ATP6V0E1 showed that only knockdown of ATP6V0E1 mimicked the effect of miR-431-5p overexpression on cell viability. Our findings indicate that miR-431-5p acts as a tumour suppressor in PDAC cells, with BxPC-3 cells being most responsive.

Rho-Associated Kinase Inhibitor Eye Drops in challenging cataract surgery

Purpose

To report the impact of Rho-Associated Kinase Inhibitor Eye Drops in cases of cataract surgery performed in severe Fuchs’ endothelial corneal dystrophy (FECD).

Observations

A patient affected by FECD stage II underwent femtosecond laser-assisted cataract surgery (FLACS), developed postsurgical corneal failure and was scheduled for endothelial keratoplasty. Compassionate treatment with Rho-Associated Kinase Inhibitor Eye Drops 4 times per day was started. A significant improvement in visual acuity and corneal failure was recorded. Thereafter, other two patients affected by FECD stage II were prophylactically treated with Rho-Associated Kinase Inhibitor Eye Drops 4 times per day for three months before FLACS with good visual and clinical outcome.

Conclusions and Importance

These cases expand upon the reported effects of rho-associated kinase inhibitor Ripasudil in the FECD, suggesting a role as adjuvant medical therapy in patients advised for intraocular surgery to improve endothelial function and reduce the risk of pseudophakic bullous keratopathy (PBK).

Insights into the post-translational modification and its emerging role in shaping the tumor microenvironment

More and more in-depth studies have revealed that the occurrence and development of tumors depend on gene mutation and tumor heterogeneity. The most important manifestation of tumor heterogeneity is the dynamic change of tumor microenvironment (TME) heterogeneity. This depends not only on the tumor cells themselves in the microenvironment where the infiltrating immune cells and matrix together forming an antitumor and/or pro-tumor network. TME has resulted in novel therapeutic interventions as a place beyond tumor beds. The malignant cancer cells, tumor infiltrate immune cells, angiogenic vascular cells, lymphatic endothelial cells, cancer-associated fibroblastic cells, and the released factors including intracellular metabolites, hormonal signals and inflammatory mediators all contribute actively to cancer progression. Protein post-translational modification (PTM) is often regarded as a degradative mechanism in protein destruction or turnover to maintain physiological homeostasis. Advances in quantitative transcriptomics, proteomics, and nuclease-based gene editing are now paving the global ways for exploring PTMs. In this review, we focus on recent developments in the PTM area and speculate on their importance as a critical functional readout for the regulation of TME. A wealth of information has been emerging to prove useful in the search for conventional therapies and the development of global therapeutic strategies.

Oxidative stress and Rho GTPases in the biogenesis of tunnelling nanotubes: implications in disease and therapy

Tunnelling nanotubes (TNTs) are an emerging route of long-range intercellular communication that mediate cell-to-cell exchange of cargo and organelles and contribute to maintaining cellular homeostasis by balancing diverse cellular stresses. Besides their role in intercellular communication, TNTs are implicated in several ways in health and disease. Transfer of pathogenic molecules or structures via TNTs can promote the progression of neurodegenerative diseases, cancer malignancy, and the spread of viral infection. Additionally, TNTs contribute to acquiring resistance to cancer therapy, probably via their ability to rescue cells by ameliorating various pathological stresses, such as oxidative stress, reactive oxygen species (ROS), mitochondrial dysfunction, and apoptotic stress. Moreover, mesenchymal stem cells play a crucial role in the rejuvenation of targeted cells with mitochondrial heteroplasmy and oxidative stress by transferring healthy mitochondria through TNTs. Recent research has focussed on uncovering the key regulatory molecules involved in the biogenesis of TNTs. However further work will be required to provide detailed understanding of TNT regulation. In this review, we discuss possible associations with Rho GTPases linked to oxidative stress and apoptotic signals in biogenesis pathways of TNTs and summarize how intercellular trafficking of cargo and organelles, including mitochondria, via TNTs plays a crucial role in disease progression and also in rejuvenation/therapy.

Rho GTPases: Non-canonical regulation by cysteine oxidation

Rho GTPases are critically important and are centrally positioned regulators of the actomyosin cytoskeleton. By influencing the organization and architecture of the cytoskeleton, Rho proteins play prominent roles in many cellular processes including adhesion, migration, intra-cellular transportation, and proliferation. The most important method of Rho GTPase regulation is via the GTPase cycle; however, post-translational modifications (PTMs) also play critical roles in Rho protein regulation. Relative to other PTMs such as lipidation or phosphorylation that have been extensively characterized, protein oxidation is a regulatory PTM that has been poorly studied. Protein oxidation primarily occurs from the reaction of reactive oxygen species (ROS), such as hydrogen peroxide (H₂ O₂ ), with amino acid side chain thiols on cysteine (Cys) and methionine (Met) residues. The versatile redox modifications of cysteine residues exemplify their integral role in cell signalling processes. Here we review prominent members of the Rho GTPase family and discuss how lipidation, phosphorylation, and oxidation on conserved cysteine residues affects their regulation and function.

Decomposition of cell activities revealing the role of the cell cycle in driving biofunctional heterogeneity

Heterogeneity of cell phenotypes remains a barrier in progressing cell research and a challenge in conquering cancer-related drug resistance. Cell morphology, the most direct property of cell phenotype, evolves along the progression of the cell cycle; meanwhile, cell motility, the dynamic property of cell phenotype, also alters over the cell cycle. However, a quantifiable research understanding the relationship between the cell cycle and cell migration is missing. Herein, we coordinate the migratory behaviours of NIH 3T3 fibroblasts to their corresponding phases of the cell cycle, the G1, the S, and the G2 phases, and explain the relationship through the spatiotemporal arrangements between the Rho GTPases’ signals and cyclin-dependent kinase inhibitors, p21^Cip1, and p27^Kip1. Taken together, we demonstrate that both cell morphology and the dynamic subcellular behaviour are homogenous within each stage of the cell cycle phases but heterogenous between phases through quantitative cell analyses and an interactive molecular mechanism between the cell cycle and cell migration, posing potential implications in countering drug resistance.

Graded RhoA GTPase Expression in Treg Cells Distinguishes Tumor Immunity From Autoimmunity

RhoA of the Rho GTPase family is prenylated at its C-terminus. Prenylation of RhoA has been shown to control T helper 17 (Th17) cell-mediated colitis. By characterizing T cell-specific RhoA conditional knockout mice, we have recently shown that RhoA is required for Th2 and Th17 cell differentiation and Th2/Th17 cell-mediated allergic airway inflammation. It remains unclear whether RhoA plays a cell-intrinsic role in regulatory T (Treg) cells that suppress effector T cells such as Th2/Th17 cells to maintain immune tolerance and to promote tumor immune evasion. Here we have generated Treg cell-specific RhoA-deficient mice. We found that homozygous RhoA deletion in Treg cells led to early, fatal systemic inflammatory disorders. The autoimmune responses came from an increase in activated CD4⁺ and CD8⁺ T cells and in effector T cells including Th17, Th1 and Th2 cells. The immune activation was due to impaired Treg cell homeostasis and increased Treg cell plasticity. Interestingly, heterozygous RhoA deletion in Treg cells did not affect Treg cell homeostasis nor cause systemic autoimmunity but induced Treg cell plasticity and an increase in effector T cells. Importantly, heterozygous RhoA deletion significantly inhibited tumor growth, which was associated with tumor-infiltrating Treg cell plasticity and increased tumor-infiltrating effector T cells. Collectively, our findings suggest that graded RhoA expression in Treg cells distinguishes tumor immunity from autoimmunity and that rational targeting of RhoA in Treg cells may trigger anti-tumor T cell immunity without causing autoimmune responses.

RhoGTPase Signalling in Cancer Progression and Dissemination

Rho GTPases are a family of small G proteins that regulate a wide array of cellular processes related to their key roles controlling the cytoskeleton. On the other hand, cancer is a multi-step disease caused by the accumulation of genetic mutations and epigenetic alterations, from the initial stages of cancer development when cells in normal tissues undergo transformation, to the acquisition of invasive and metastatic traits, responsible for a large number of cancer related deaths. In this review, we discuss the role of Rho GTPase signalling in cancer in every step of disease progression. Rho GTPases contribute to tumour initiation and progression, by regulating proliferation and apoptosis, but also metabolism, senescence and cell stemness. Rho GTPases play a major role in cell migration, and in the metastatic process. They are also involved in interactions with the tumour microenvironment and regulate inflammation, contributing to cancer progression. After years of intensive research, we highlight the importance of relevant models in the Rho GTPase field, and we reflect on the therapeutic opportunities arising for cancer patients.

Y-27632 Promotes the Repair Effect of Umbilical Cord Blood-Derived Endothelial Progenitor Cells on Corneal Endothelial Wound Healing

PURPOSE

To investigate the proliferation of umbilical cord blood-derived endothelial progenitor cells (UCB EPCs) and the differentiation efficiency toward corneal endothelial cell (CEC)-like cells induced by rho-associated protein kinase (ROCK) inhibitor Y-27632 and to determine the most effective strategy for repairing corneal endothelium injuries in rabbits.

METHODS

UCB EPCs were cultured in Endothelial Cell Growth Medium-2 (EGM-2) media or conditioned media (CM) from human CECs, with and without the addition of Y-27632. Bromo-deoxyuridine (BrdU) immunocytochemistry and cell counting kit-8 assays were used to examine the proliferation of the cells. Real-time polymerase chain reaction, western blot, and immunocytochemistry were used to detect the CEC markers. Nd:YAG laser was used to establish an appropriate endothelium injury model based on rabbit corneas. The following intracameral injections were then performed to repair the model: 100 μL Opti-MEM I reduced serum medium (model group), 2 × 105 UCB EPCs diluted in 100 μL Opti-MEM I reduced serum medium (EPC group), 100 μM Y-27632 diluted in 100 μL Opti-MEM I reduced serum medium (Y-27632 group), and 2 × 105 UCB EPCs supplemented with 100 μM Y-27632 (final volume 100 μL, EPC/Y-27632 group). The follow-up tests focused on corneal transparency, central corneal thickness, intraocular pressure, and in vivo confocal microscopy, which were performed to evaluate the healing of the wounds.

RESULTS

Culturing UCB EPCs in CM supplemented with 10 μM Y-27632 resulted in higher proliferation rates compared with EGM-2 media and CM. There were significantly improved protein levels of Zona Occludens 1, N-cadherin, Na+-K+-ATPase α1, Na+-K+-ATPase β1, and Pax6 and improved mRNA levels of collagen type IV and VIII and AQP1. The combined intracameral injection of Y-27632 and UCB EPCs accelerated the recovery of corneal transparency, regression of corneal edema, and healing of the corneal endothelium compared with the injections of Y-27632 and UCB EPCs on their own.

CONCLUSIONS

Y-27632 not only promotes the proliferation of UCB EPCs but also contributes to differentiation of UCB EPCs toward CECs in the presence of CM. The intracameral injection of Y-27632 itself promotes the healing of corneal endothelium wounds. On this basis, supplementing UCB EPCs with Y-27632 accelerates the healing of corneal endothelium wounds.

Challenges in corneal endothelial cell culture

Corneal endothelial cells (CECs) facilitate the function of maintaining the transparency of the cornea. Damage or dysfunction of CECs can lead to blindness, and the primary treatment is corneal transplantation. However, the shortage of cornea donors is a significant problem worldwide. Thus, cultured CEC therapy has been proposed and found to be a promising approach to overcome the lack of tissue supply. Unfortunately, CECs in humans rarely proliferate in vivo and, therefore, can be extremely challenging to culture in vitro. Several promising cell isolation and culture techniques have been proposed. Multiple factors affecting the success of cell expansion including donor characteristics, preservation and isolation methods, plating density, media preparation, transdifferentiation and biomarkers have been evaluated. However, there is no consensus on standard technique for CEC culture. This review aimed to determine the challenges and investigate potential options that would facilitate the standardization of CEC culture for research and therapeutic application.

Potential Effect of Human Platelet Lysate on in vitro Expansion of Human Corneal Endothelial Cells Compared with Y-27632 ROCK Inhibitor

Purpose

Corneal endothelial cell (CEC) therapy can be used as a promising therapeutic option for patients with various corneal endothelial dysfunctions. In this study, we compared the proliferative effect of human platelet lysate (HPL), as a xeno-free medium supplement, with Y-27632 Rho/rho-associated protein kinase (ROCK) inhibitor, as a well-known proliferative and adhesive agent for CECs, and fetal bovine serum (FBS) as the control, in the culture medium of human corneal endothelial cells (HCECs).

Methods

We isolated HCECs from human donors and treated the cells as three different treatment groups including 20% HPL only, 10 μM Y-27632 ROCK inhibitor, combination of 20% HPL and 10 μM Y-27632 ROCK inhibitor, and 20% FBS as the control group. ELISA cell proliferation assay and cell counting was performed on the treated cells. Finally, HCECs were characterized by morphology and immunocytochemistry (ICC).

Results

There was no significant proliferative effect of HPL on cell proliferation compared with the cells treated with Y-27632 ROCK inhibitor or the combination of HPL and Y-27632 ROCK inhibitor, but all the respected treatments had significant inducible effect on cell proliferation as compared with FBS-treated cells. The cells grown in all three treatment groups exhibited CEC morphology. Also, there was a higher expression of Na+/K+-ATPase and ZO-1, as CEC characteristic markers, in the culture of HCECs treated with HPL as compared with FBS.

Conclusion

HPL offers a xeno-free and affordable medium supplement for CEC expansion that can be used in clinical applications.

Small Rho GTPases and their associated RhoGEFs mutations promote immunological defects in primary immunodeficiencies

Primary immunodeficiencies (PIDs) are associated with deleterious mutations of genes that encode proteins involved in actin cytoskeleton reorganisation. This deficiency affects haematopoietic cells. PID results in the defective function of immune cells, such as impaired chemokine-induced motility, receptor signalling, development and maturation. Some of the genes mutated in PIDs are related to small Ras homologous (Rho) guanosine triphosphatase (GTPase), one of the families of the Ras superfamily. Most of these genes act as molecular switches by cycling between active guanosine triphosphate-bound and inactive guanosine diphosphate-bound forms to control multiple cellular functions. They are best studied for their role in promoting cytoskeleton reorganisation, cell adhesion and motility. Currently, only three small Rho GTPases, namely, Rac2, Cdc42 and RhoH, have been identified in PIDs. However, several other Rho small G proteins might also contribute to the deregulation and phenotype observed in PIDs. Their contribution in PIDs may involve their main regulator, Rho guanine nucleotide exchange factors such as DOCK2 and DOCK8, wherein mutations may result in the impairment of small Rho GTPase activation. Thus, this review outlines the potential contribution of several small Rho GTPases to the promotion of PIDs.

Distinct Roles for Rac1 in Sertoli Cell Function during Testicular Development and Spermatogenesis

Sertoli cells are supporting cells of the testicular seminiferous tubules, which provide a nurturing environment for spermatogenesis. Adult Sertoli cells are polarized so that they can simultaneously support earlier-stage spermatogenic cells (e.g., spermatogonia) basally and later-stage cells (e.g., spermatids) apically. To test the consequences of disrupting cell polarity in Sertoli cells, we perform a Sertoli-specific conditional deletion of Rac1, which encodes a Rho GTPase required for apicobasal cell polarity. Rac1 conditional knockout adults exhibit spermatogenic arrest at the round spermatid stage, with severe disruption of Sertoli cell polarity, and show increased germline and Sertoli cell apoptosis. Thus, Sertoli Rac1 function is critical for the progression of spermatogenesis but, surprisingly, is dispensable for fetal testicular development, adult maintenance of undifferentiated spermatogonia, and meiotic entry. Our data indicate that Sertoli Rac1 function is required only for certain aspects of spermatogenesis and reveal that there are distinct requirements for cell polarity during cellular differentiation.

Effects of isoprenylcysteine carboxyl methyltransferase silencing on the proliferation and apoptosis of tongue squamous cell carcinoma

OBJECTIVES

This study aimed to explore the effects of silencing isoprenylcysteine carboxyl methyltransfe-rase (Icmt) through small interfering RNA (siRNA) interference on the proliferation and apoptosis of tongue squamous cell carcinoma (TSCC).

METHODS

Three siRNA were designed and constructed for the Icmt gene sequence and were then transfected into TSCC cells CAL-27 and SCC-4 to silence Icmt expression. The tested cells were divided as follows: RNA interference groups Icmt-siRNA-1, Icmt-siRNA-2, and Icmt-siRNA-3, negative control group, and blank control group. The transfection efficiency of siRNA was detected by the fluorescent group Cy3-labeled siRNA, and the expression of Icmt mRNA was screened by quantitive real-time polymerase chain reaction (qRT-PCR) selected the experimental group for subsequent experiments. The expression of Icmt, RhoA, Cyclin D1, p21, extracellular regulated protein kinases (ERK), and phospho-extracellular regulated protein kinases (p-ERK) were analyzed by Western blot. The proliferation abilities of TSCC cells were determined by cell counting kit-8 assay. The change in apoptosis was detected by AnnexinV-APC/propidium staining (PI) assay. Cell-cycle analysis was conducted by flow cytometry.

RESULTS

The expression of Icmt mRNA and protein in TSCC cells significantly decreased after Icmt-siRNA transfection (P<0.05). No significant difference in RhoA mRNA and protein expression was detected (P>0.05), but the expression of RhoA membrane protein decreased compared with the negative control group and blank control groups (P<0.05). Cyclin D1 expression decreased, whereas p21 expression significantly increased and the relative expression of ERK protein in the experimental group did not significantly different that in the control group (P>0.05). However, the phosphorylation level of ERK was significantly reduced (P<0.05). The cell cycles of TSCC CAL-27 and SCC-4 were altered in G1/S, cell proliferation activity was inhibited, and apoptosis was induced (P<0.05).

CONCLUSIONS

Silencing Icmt can effectively downregulate its expression in TSCC cells, reduce the RhoA membrane targeting localization and cell proliferation, and induce apoptosis. Thus, Icmt may be a potential gene therapy target for TSCC.

Aberrant Rac pathway signalling in glioblastoma

Glioblastoma is an aggressive and incurable form of brain cancer. Both mutation analysis in human glioblastoma and mouse modelling studies have shown that aberrant activation of the PI 3-kinase pathway is a central driver of glioblastoma malignancy. The small GTPase Rac is activated downstream of this pathway, mediating a subset of the effects of aberrant PI 3-kinase pathway activation. Here I discuss the current state of our knowledge on Rac activation mechanisms in glioblastoma. Current knowledge on roles for specific PI 3-kinase pathway responsive Rac guanine nucleotide exchange factors in glioblastoma is reviewed. Rac is best known for its role in promoting cell motility and invasion, but there is also evidence for roles in multiple other cellular processes with cancer relevance, including proliferation, differentiation, apoptosis, DNA damage responses, metabolism, angiogenesis and immunosuppression. I review what is known about the role of Rac in these processes in glioblastoma. Finally, I assess possible strategies to inhibit this pathway in glioblastoma through either direct inhibition of Rac or inhibition of upstream activators or downstream mediators of Rac signalling.

The structure and function of protein kinase C-related kinases (PRKs)

The protein kinase C-related kinase (PRK) family of serine/threonine kinases, PRK1, PRK2 and PRK3, are effectors for the Rho family small G proteins. An array of studies have linked these kinases to multiple signalling pathways and physiological roles, but while PRK1 is relatively well-characterized, the entire PRK family remains understudied. Here, we provide a holistic overview of the structure and function of PRKs and describe the molecular events that govern activation and autoregulation of catalytic activity, including phosphorylation, protein interactions and lipid binding. We begin with a structural description of the regulatory and catalytic domains, which facilitates the understanding of their regulation in molecular detail. We then examine their diverse physiological roles in cytoskeletal reorganization, cell adhesion, chromatin remodelling, androgen receptor signalling, cell cycle regulation, the immune response, glucose metabolism and development, highlighting isoform redundancy but also isoform specificity. Finally, we consider the involvement of PRKs in pathologies, including cancer, heart disease and bacterial infections. The abundance of PRK-driven pathologies suggests that these enzymes will be good therapeutic targets and we briefly report some of the progress to date.

Manipulation of Focal Adhesion Signaling by Pathogenic Microbes

Focal adhesions (FAs) serve as dynamic signaling hubs within the cell. They connect intracellular actin to the extracellular matrix (ECM) and respond to environmental cues. In doing so, these structures facilitate important processes such as cell-ECM adhesion and migration. Pathogenic microbes often modify the host cell actin cytoskeleton in their pursuit of an ideal replicative niche or during invasion to facilitate uptake. As actin-interfacing structures, FA dynamics are also intimately tied to actin cytoskeletal organization. Indeed, exploitation of FAs is another avenue by which pathogenic microbes ensure their uptake, survival and dissemination. This is often achieved through the secretion of effector proteins which target specific protein components within the FA. Molecular mimicry of the leucine-aspartic acid (LD) motif or vinculin-binding domains (VBDs) commonly found within FA proteins is a common microbial strategy. Other effectors may induce post-translational modifications to FA proteins through the regulation of phosphorylation sites or proteolytic cleavage. In this review, we present an overview of the regulatory mechanisms governing host cell FAs, and provide examples of how pathogenic microbes have evolved to co-opt them to their own advantage. Recent technological advances pose exciting opportunities for delving deeper into the mechanistic details by which pathogenic microbes modify FAs.

Ror2-mediated non-canonical Wnt signaling regulates Cdc42 and cell proliferation during tooth root development

The control of size and shape is an important part of regulatory process during organogenesis. Tooth formation is a highly complex process that fine-tunes the size and shape of the tooth, which are crucial for its physiological functions. Each tooth consists of a crown and one or more roots. Despite comprehensive knowledge of the mechanism that regulates early tooth crown development, we have limited understanding of the mechanism regulating root patterning and size during development. Here, we show that Ror2-mediated non-canonical Wnt signaling in the dental mesenchyme plays a crucial role in cell proliferation, and thereby regulates root development size in mouse molars. Furthermore, Cdc42 acts as a potential downstream mediator of Ror2 signaling in root formation. Importantly, activation of Cdc42 can restore cell proliferation and partially rescue the root development size defects in Ror2 mutant mice. Collectively, our findings provide novel insights into the function of Ror2-mediated non-canonical Wnt signaling in regulating tooth morphogenesis, and suggest potential avenues for dental tissue engineering.

Summary: The function of Ror2-mediated non-canonical Wnt signaling and its effect on Cdc42 activation is crucial in regulating progenitor cell proliferation, odontoblast differentiation and Hertwig's epithelial root sheath formation during tooth root morphogenesis.

Inhibition of p70 isoforms of S6K1 induces anoikis to prevent transformed human hepatocyte growth

AIMS

The mTOR/S6K1 signaling axis, known for cell growth regulation, is hyper-activated in multiple cancers. In this study, we have examined the mechanisms for ribosomal protein p70-S6 kinase 1 (S6K1) associated transformed human hepatocyte (THH) growth regulation.

MAIN METHODS

THH were treated with p70-S6K1 inhibitor and analyzed for cell viability, cell cycle distribution, specific marker protein expression by western blot, and tumor inhibition in a xenograft mouse model. We validated our results by knockdown of p70-S6K1 using specific siRNA.

KEY FINDINGS

p70-S6K1 inhibitor treatment caused impairment of in vitro hepatocyte growth, and arrested cell cycle progression at the G1 phase. Further, p70-S6K1 inhibitor treatment exhibited a decrease in FAK and Erk activation, followed by altered integrin-β1 expression, caspase 8, and PARP cleavage appeared to be anoikis like growth inhibition. p70-S6K1 inhibitor also depolymerized actin microfilaments and diminished active Rac1/Cdc42 complex formation for loss of cellular attachment. Similar results were obtained with other transformed human hepatocyte cell lines. p70-S6K1 inhibition also resulted in a reduced phospho-EGFR, Slug and Twist; implicating an inhibition of epithelial-mesenchymal transition (EMT) state. A xenograft tumor model, generated from implanted THH in nude mice, following intraperitoneal injection of S6K1 inhibitor prevented further tumor growth.

SIGNIFICANCE

Our results suggested that p70-S6K1 inhibition alters orchestration of cell cycle progression, induces cell detachment, and sensitizes hepatocyte growth impairment. Targeting p70 isoform of S6K1 by inhibitor may prove to be a promising approach together with other therapies for hepatocellular carcinoma (HCC) treatment.

RhoA and Cdc42 in T cells: Are they targetable for T cell-mediated inflammatory diseases?

Many inflammatory diseases are not curable, necessitating a better understanding of their pathobiology that may help identify novel biological targets. RhoA and Cdc42 of Rho family small GTPases regulate a variety of cellular functions such as actin cytoskeletal organization, cell adhesion, migration, proliferation, and survival. Recent characterization of mouse models of conditional gene knockout of RhoA and Cdc42 has revealed their physiological and cell type-specific roles in a number of cell types. In T lymphocytes, which play an important role in the pathogenesis of most, if not all, of the inflammatory diseases, we and others have investigated the effects of T cell-specific knockout of RhoA and Cdc42 on T cell development in the thymus, peripheral T cell homeostasis, activation, and differentiation to effector and regulatory T cells, and on T cell-mediated allergic airway inflammation and colitis. Here we highlight the phenotypes resulting from RhoA and Cdc42 deletion in T cells and discuss whether pharmacological targeting of RhoA and Cdc42 is feasible in treating asthma that is driven by allergic airway inflammation and colitis.

A perspective on the early days of RAS research

The name of the oncogene, ras, has its origin in studies of murine leukemia viruses in the 1960s by Jenny Harvey (H-ras) and by Werner Kirsten (K-ras) which, at high doses, produced sarcomas in rats. Transforming retroviruses were isolated, and its oncogene was named ras after rat sarcoma. From 1979, cellular ras sequences with transforming properties were identified by transfection of tumor DNA initially by Robert Weinberg from rodent tumors, and the isolation of homologous oncogenes from human tumors soon followed, including HRAS and KRAS, and a new member of the family named NRAS. I review these discoveries, placing emphasis on the pioneering research of Christopher Marshall and Alan Hall, who subsequently made immense contributions to our understanding of the functions of RAS and related small GTPases to signal transduction pathways, cell structure, and the behavior of normal and malignant cells.

Coordination between Cell Motility and Cell Cycle Progression in Keratinocyte Sheets via Cell-Cell Adhesion and Rac1

Regulations of cell motility and proliferation are essential for epithelial development and homeostasis. However, it is not fully understood how these cellular activities are coordinated in epithelial collectives. In this study, we find that keratinocyte sheets exhibit time-dependent coordination of collective cell movement and cell cycle progression after seeding cells. Cell movement and cell cycle progression are coordinately promoted by Rac1 in the “early phase” (earlier than ∼30 h after seeding cells), which is not abrogated by increasing the initial cell density to a saturated level. The Rac1 activity is gradually attenuated in the “late phase” (later than ∼30 h after seeding cells), leading to arrests in cell motility and cell cycle. Intact adherens junctions are required for normal coordination between cell movement and cell cycle progression in both early and late phases. Our results unveil a novel basis for integrating motile and proliferative behaviors of epithelial collectives.

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Cell motility and cell cycle progression in keratinocyte sheets are temporally coordinated

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Rac1 promotes both cell motility and cell cycle progression in keratinocyte sheets

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Arrest of cell motility and cell cycle is associated with Rac1 deactivation

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Adherens junction is required for coordinating cell motility and cell cycle

HCF-1 promotes cell cycle progression by regulating the expression of CDC42

The eukaryotic cell cycle involves a highly orchestrated series of events in which the cellular genome is replicated during a synthesis (S) phase and each of the two resulting copies are segregated properly during mitosis (M). Host cell factor-1 (HCF-1) is a transcriptional co-regulator that is essential for and has been implicated in basic cellular processes, such as transcriptional regulation and cell cycle progression. Although a series of HCF-1 transcriptional targets have been identified, few functional clues have been provided, especially for chromosome segregation. Our results showed that HCF-1 activated CDC42 expression by binding to the −881 to −575 region upstream of the CDC42 transcription start site, and the regulation of CDC42 expression by HCF-1 was correlated with cell cycle progression. The overexpression of a spontaneously cycling and constitutively active CDC42 mutant (CDC42F28L) rescued G1 phase delay and multinucleate defects in mitosis upon the loss of HCF-1. Therefore, these results establish that HCF-1 ensures proper cell cycle progression by regulating the expression of CDC42, which indicates a possible mechanism of cell cycle coordination and the regulation mode of typical Rho GTPases.

FoxM1 insufficiency hyperactivates Ect2-RhoA-mDia1 signaling to drive cancer

FoxM1 activates genes that regulate S-G2-M cell-cycle progression and, when overexpressed, is associated with poor clinical outcome in multiple cancers. Here we identify FoxM1 as a tumor suppressor in mice that, through its N-terminal domain, binds to and inhibits Ect2 to limit the activity of RhoA GTPase and its effector mDia1, a catalyst of cortical actin nucleation. FoxM1 insufficiency impedes centrosome movement through excessive cortical actin polymerization, thereby causing the formation of non-perpendicular mitotic spindles that missegregate chromosomes and drive tumorigenesis in mice. Importantly, low FOXM1 expression correlates with RhoA GTPase hyperactivity in multiple human cancer types, indicating that suppression of the newly discovered Ect2-RhoAmDia1 oncogenic axis by FoxM1 is clinically relevant. Furthermore, by dissecting the domain requirements through which FoxM1 inhibits Ect2 GEF activity, we provide mechanistic insight for the development of pharmacological approaches that target protumorigenic RhoA activity.

Clostridial C3 Toxins Enter and Intoxicate Human Dendritic Cells

C3 protein toxins produced by Clostridium (C.) botulinum and C. limosum are mono-ADP-ribosyltransferases, which specifically modify the GTPases Rho A/B/C in the cytosol of monocytic cells, thereby inhibiting Rho-mediated signal transduction in monocytes, macrophages, and osteoclasts. C3 toxins are selectively taken up into the cytosol of monocytic cells by endocytosis and translocate from acidic endosomes into the cytosol. The C3-catalyzed ADP-ribosylation of Rho proteins inhibits essential functions of these immune cells, such as migration and phagocytosis. Here, we demonstrate that C3 toxins enter and intoxicate dendritic cells in a time- and concentration-dependent manner. Both immature and mature human dendritic cells efficiently internalize C3 exoenzymes. These findings could also be extended to the chimeric fusion toxin C2IN-C3lim. Moreover, stimulated emission depletion (STED) microscopy revealed the localization of the internalized C3 protein in endosomes and emphasized its potential use as a carrier to deliver foreign proteins into dendritic cells. In contrast, the enzyme C2I from the binary C. botulinum C2 toxin was not taken up into dendritic cells, indicating the specific uptake of C3 toxins. Taken together, we identified human dendritic cells as novel target cells for clostridial C3 toxins and demonstrated the specific uptake of these toxins via endosomal vesicles.

Overactivated Cdc42 acts through Cdc42EP3/Borg2 and NCK to trigger DNA damage response signaling and sensitize cells to DNA-damaging agents

The small GTPase Cdc42, a member of the Rho family, regulates essential biological processes such as cytoskeleton remodeling, migration, vesicular trafficking and cell cycle. It was demonstrated that Cdc42 overactivation through different molecular strategies increases cell sensitivity to genotoxic stress and affects the phosphorylation status of DNA damage response proteins by unknown mechanisms. By using a combination of approaches including affinity purification/mass spectrometry (AP/MS) and colocalization microscopy analysis we were able to identify Cdc42EP3/Borg2 as a putative molecular effector of these molecular and cellular events that seem to be independent of cell line or DNA damage stimuli. We then investigated the influence of Cdc42EP3/Borg2 and other potential protein partners, such as the NCK and Septin2 proteins, which could mediate cellular responses to genotoxic stress under different backgrounds of Cdc42 activity. Clonogenic assays showed a reduced cell survival when ectopically expressing the Cdc42EP3/Borg2, NCK2 or Septin2 in an overactivated Cdc42-dependent background. Moreover, endogenous NCK appears to relocate into the nucleus upon Cdc42 overactivation, especially under genotoxic stress, and promotes the suppression of Chk1 phosphorylation. In sum, our findings reinforce Cdc42 as an important player involved in the DNA damage response acting through Cdc42EP3/Borg2 and NCK proteins following genomic instability conditions.

Molecular cloning and characterization of DjRac1, a novel small G protein gene from planarian Dugesia japonica

Rac proteins are classified as a subfamily of the Rho family of small G proteins. They are important molecular switches which act as key signal transducers regulating a wide variety of processes in the cell. DjRac1, a novel Rac gene from planarian Dugesia japonica was cloned by RACE method and characterized. This cDNA contains 851 bp with a putative open reading frame of 190 amino acids. It has a predicted molecular mass of 21.12 kDa and an isoelectric point of 8.42. Whole-mount in situ hybridization and relative quantitative real-time PCR were used to study the spatial and temporal expression pattern of DjRac1 from 1 to 7 days in the regenerating planarians. Results showed that the expression of DjRac1 was concentrated in the blastema and the transcription level of DjRac1 was significantly upregulated after amputation within three days, suggesting DjRac1 might participate in the process of regeneration in planarian.

The β-Carboline Harmine Induces Actin Dynamic Remodeling and Abrogates the Malignant Phenotype in Tumorigenic Cells

Numerous studies have shown that alteration of actin remodeling plays a pivotal role in the regulation of morphologic and phenotypic changes leading to malignancy. In the present study, we searched for drugs that can regulate actin polymerization and reverse the malignant phenotype in cancer cells. We developed a cell-free high-throughput screening assay for the identification of compounds that induce the actin polymerization in vitro, by fluorescence anisotropy. Then, the potential of the hit compound to restore the actin cytoskeleton and reverse the malignant phenotype was checked in EWS-Fli1-transformed fibroblasts and in B16-F10 melanoma cells. A β-carboline extracted from Peganum harmala (i.e., harmine) is identified as a stimulator of actin polymerization through a mechanism independent of actin binding and requiring intracellular factors involved in a process that regulates actin kinetics. Treatment of malignant cells with non-cytotoxic concentrations of harmine induces the recovery of a non-malignant cell morphology accompanied by reorganization of the actin cytoskeleton, rescued cell–cell adhesion, inhibition of cell motility and loss of anchorage-independent growth. In conclusion, harmine induces the reversion of the malignant phenotype by a process involving the modulation of actin dynamics and is a potential anti-tumor agent acting principally through a non-cytotoxic process.

GLP-2, EGF, and the Intestinal Epithelial IGF-1 Receptor Interactions in the Regulation of Crypt Cell Proliferation

Glucagon-like peptide-2 (GLP-2) is an intestinotrophic hormone that promotes intestinal growth and proliferation through downstream mediators, including epidermal growth factor (EGF) and insulin-like growth factor-1 (IGF-1). EGF synergistically enhances the proliferative actions of IGF-1 in intestinal cell lines, and both of these factors are known to be essential for the trophic effects of GLP-2 in vivo. However, whether EGF and IGF-1 interact to mediate the proliferative actions of GLP-2 in vivo remains unknown. Normal and knockout (KO) mice lacking the intestinal epithelial IGF-1 receptor (IE-IGF-1R) were therefore treated chronically with EGF and/or long-acting human hGly2GLP-2, followed by determination of intestinal growth parameters. Intestines from control and IE-IGF-1R KO mice were also used to generate organoids (which lack the GLP-2 receptor) and were treated with EGF and/or IGF-1. Combination treatment with EGF and hGly2GLP-2 increased small intestinal weight and crypt-villus height in C57Bl/6 mice in an additive manner, whereas only hGly2GLP-2 treatment increased crypt cell proliferation. However, although combination treatment also increased small intestinal weight and crypt-villus height in IE-IGF-1R KO mice, the proliferative responses to hGly2GLP-2 alone or with EGF were diminished in these animals. Finally, IGF-1 treatment of organoids undergoing EGF withdrawal was not additive to the effect of EGF replacement on proliferation, but could restore normal proliferation in the absence of EGF. Together, these findings demonstrate that the intestinal proliferative effects of hGly2GLP-2 are augmented by exogenous EGF in a manner that is partially dependent upon IE-IGF-1R signaling.

Colorectal cancer (CRC) as a multifactorial disease and its causal correlations with multiple signaling pathways

Colorectal cancer (CRC) is the third most common malignancy and one of the leading causes of cancer-related death among men worldwide. CRC is a multifactor digestive pathology, which is a huge problem faced not only by clinicians but also by researchers. Importantly, a unique feature of CRC is the dysregulation of molecular signaling pathways. To date, a series of reviews have indicated that different signaling pathways are disordered and have potential as therapeutic targets in CRC. Nevertheless, an overview of the function and interaction of multiple signaling pathways in CRC is needed. Therefore, we summarized the pathways, biological functions and important interactions involved in CRC. First, we investigated the involvement of signaling pathways, including Wnt, PI3K/Akt, Hedgehog, ErbB, RHOA, Notch, BMP, Hippo, AMPK, NF-κB, MAPK and JNK. Subsequently, we discussed the biological function of these pathways in pathophysiological aspects of CRC, such as proliferation, apoptosis and metastasis. Finally, we summarized important interactions among these pathways in CRC. We believe that the interaction of these pathways could provide new strategies for the treatment of CRC.

Lederer C, Kleanthous M, Drousiotou A, Malekkou A. Acid Ceramidase Depletion Impairs Neuronal Survival and Induces Morphological Defects in Neurites Associated with Altered Gene Transcription and Sphingolipid Content

The ASAH1 gene encodes acid ceramidase (AC), an enzyme that is implicated in the metabolism of ceramide (Cer). Mutations in the ASAH1 gene cause two different disorders, Farber disease (FD), a rare lysosomal storage disorder, and a rare form of spinal muscular atrophy combined with progressive myoclonic epilepsy (SMA-PME). In the absence of human in vitro neuronal disease models and to gain mechanistic insights into pathological effects of ASAH1 deficiency, we established and characterized a stable ASAH1 knockdown (ASAH1KD) SH-SY5Y cell line. ASAH1KD cells displayed reduced proliferation due to elevated apoptosis and G1/S cell cycle arrest. Distribution of LAMP1-positive lysosomes towards the cell periphery and significantly shortened and less branched neurites upon differentiation, implicate AC for lysosome positioning and neuronal development, respectively. Lipidomic analysis revealed changes in the intracellular levels of distinct sphingolipid species, importantly without Cer accumulation, in line with altered gene transcription within the sphingolipid pathway. Additionally, the transcript levels for Rho GTPases (RhoA, Rac1, and Cdc42), which are key regulators of axonal orientation, neurite branching and lysosome positioning were found to be dysregulated. This study shows the critical role of AC in neurons and suggests how AC depletion leads to defects seen in neuropathology of SMA-PME and FD.

Rac-GEF/Rac Signaling and Metastatic Dissemination in Lung Cancer

Lung cancer is the leading cause of cancer-related deaths worldwide, with non-small cell lung cancer (NSCLC) representing ∼85% of new diagnoses. The disease is often detected in an advanced metastatic stage, with poor prognosis and clinical outcome. In order to escape from the primary tumor, cancer cells acquire highly motile and invasive phenotypes that involve the dynamic reorganization of the actin cytoskeleton. These processes are tightly regulated by Rac1, a small G-protein that participates in the formation of actin-rich membrane protrusions required for cancer cell motility and for the secretion of extracellular matrix (ECM)-degrading proteases. In this perspective article we focus on the mechanisms leading to aberrant Rac1 signaling in NSCLC progression and metastasis, highlighting the role of Rac Guanine nucleotide Exchange Factors (GEFs). A plausible scenario is that specific Rac-GEFs activate discrete intracellular pools of Rac1, leading to unique functional responses in the context of specific oncogenic drivers, such as mutant EGFR or mutant KRAS. The identification of dysregulated Rac signaling regulators may serve to predict critical biomarkers for metastatic disease in lung cancer patients, ultimately aiding in refining patient prognosis and decision-making in the clinical setting.

A non-canonical role for p27Kip1 in restricting proliferation of corneal endothelial cells during development

The cell cycle regulator p27^Kip1 is a critical factor controlling cell number in many lineages. While its anti-proliferative effects are well-established, the extent to which this is a result of its function as a cyclin-dependent kinase (CDK) inhibitor or through other known molecular interactions is not clear. To genetically dissect its role in the developing corneal endothelium, we examined mice harboring two loss-of-function alleles, a null allele (p27⁻) that abrogates all protein function and a knockin allele (p27^CK−) that targets only its interaction with cyclins and CDKs. Whole-animal mutants, in which all cells are either homozygous knockout or knockin, exhibit identical proliferative increases (~0.6-fold) compared with wild-type tissues. On the other hand, use of mosaic analysis with double markers (MADM) to produce infrequently-occurring clones of wild-type and mutant cells within the same tissue environment uncovers a roughly three- and six-fold expansion of individual p27^CK−/CK− and p27^−/− cells, respectively. Mosaicism also reveals distinct migration phenotypes, with p27^−/− cells being highly restricted to their site of production and p27^CK−/CK− cells more widely scattered within the endothelium. Using a density-based clustering algorithm to quantify dispersal of MADM-generated clones, a four-fold difference in aggregation is seen between the two types of mutant cells. Overall, our analysis reveals that, in developing mouse corneal endothelium, p27 regulates cell number by acting cell autonomously, both through its interactions with cyclins and CDKs and through a cyclin-CDK-independent mechanism(s). Combined with its parallel influence on cell motility, it constitutes a potent multi-functional effector mechanism with major impact on tissue organization.

Enhanced Dendritic Actin Network Formation in Extended Lamellipodia Drives Proliferation in Growth-Challenged Rac1P29S Melanoma Cells

Actin assembly supplies the structural framework for cell morphology and migration. Beyond structure, this actin framework can also be engaged to drive biochemical signaling programs. Here, we describe how the hyperactivation of Rac1 via the P29S mutation (Rac1^P29S) in melanoma hijacks branched actin network assembly to coordinate proliferative cues that facilitate metastasis and drug resistance. Upon growth challenge, Rac1^P29S-harboring melanoma cells massively upregulate lamellipodia formation by dendritic actin polymerization. These extended lamellipodia form a signaling microdomain that sequesters and phospho-inactivates the tumor suppressor NF2/Merlin, driving Rac1^P29S cell proliferation in growth suppressive conditions. These biochemically active lamellipodia require cell-substrate attachment but not focal adhesion assembly and drive proliferation independently of the ERK/MAPK pathway. These data suggest a critical link between cell morphology and cell signaling and reconcile the dichotomy of Rac1's regulation of both proliferation and actin assembly by revealing a mutual signaling axis wherein actin assembly drives proliferation in melanoma.