Integrin signaling via FAK-Src controls cytokinetic abscission by decelerating PLK1 degradation and subsequent recruitment of CEP55 at the midbody

Targeting focal adhesion kinase (FAK) in cancer therapy: A recent update on inhibitors and PROTAC degraders

Focal adhesion kinase (FAK) is considered as a pivotal intracellular non-receptor tyrosine kinase, and has garnered significant attention as a promising target for anticancer drug development. As of early 2024, a total of 12 drugs targeting FAK have been approved for clinical or preclinical studies worldwide, including three PROTAC degraders. In recent three years (2021-2023), significant progress has been made in designing targeted FAK anticancer agents, including the development of a novel benzenesulfofurazan type NO-releasing FAK inhibitor and the first-in-class dual-target inhibitors simultaneously targeting FAK and HDACs. Given the pivotal role of FAK in the discovery of anticancer drugs, as well as the notable advancements achieved in FAK inhibitors and PROTAC degraders in recent years, this review is underbaked to present a comprehensive overview of the function and structure of FAK. Additionally, the latest findings on the inhibitors and PROTAC degraders of FAK from the past three years, along with their optimization strategies and anticancer activities, were summarized, which might help to provide novel insights for the development of novel targeted FAK agents with promising anticancer potential and favorable pharmacological profiles.

Cell-Specific Impacts of Surface Coating Composition on Extracellular Vesicle Secretion

Biomaterial properties have recently been shown to modulate extracellular vesicle (EV) secretion and cargo; however, the effects of substrate composition on EV production remain underexplored. This study investigates the impacts of surface coatings composed of collagen I (COLI), fibronectin (FN), and poly l-lysine (PLL) on EV secretion for applications in therapeutic EV production and to further understanding of how changes in the extracellular matrix microenvironment affect EVs. EV secretion from primary bone marrow-derived mesenchymal stromal cells (BMSCs), primary adipose-derived stem cells (ASCs), HEK293 cells, NIH3T3 cells, and RAW264.7 cells was characterized on the different coatings. Expression of EV biogenesis genes and cellular adhesion genes was also analyzed. COLI coatings significantly decreased EV secretion in RAW264.7 cells, with associated decreases in cell viability and changes in EV biogenesis-related and cell adhesion genes at day 4. FN coatings increased EV secretion in NIH3T3 cells, while PLL coatings increased EV secretion in ASCs. Surface coatings had significant effects on the capacity of EVs derived from RAW264.7 and NIH3T3 cells to impact in vitro macrophage proliferation. Overall, surface coatings had different cell-specific effects on EV secretion and in vitro functional capacity, thus highlighting the potential of substrate coatings to further the development of clinical EV production systems.

CEBP-β and PLK1 as Potential Mediators of the Breast Cancer/Obesity Crosstalk: In Vitro and In Silico Analyses

Over the last two decades, obesity has reached pandemic proportions in several countries, and expanding evidence is showing its contribution to several types of malignancies, including breast cancer (BC). The conditioned medium (CM) from mature adipocytes contains a complex of secretes that may mimic the obesity condition in studies on BC cell lines conducted in vitro. Here, we report a transcriptomic analysis on MCF-7 BC cells exposed to adipocyte-derived CM and focus on the predictive functional relevance that CM-affected pathways/processes and related biomarkers (BMs) may have in BC response to obesity. CM was demonstrated to increase cell proliferation, motility and invasion as well as broadly alter the transcript profiles of MCF-7 cells by significantly modulating 364 genes. Bioinformatic functional analyses unraveled the presence of five highly relevant central hubs in the direct interaction networks (DIN), and Kaplan-Meier analysis sorted the CCAAT/enhancer binding protein beta (CEBP-β) and serine/threonine-protein kinase PLK1 (PLK1) as clinically significant biomarkers in BC. Indeed, CEBP-β and PLK1 negatively correlated with BC overall survival and were up-regulated by adipocyte-derived CM. In addition to their known involvement in cell proliferation and tumor progression, our work suggests them as a possible "deus ex machina" in BC response to fat tissue humoral products in obese women.

Design, Synthesis and Antitumor Activity of FAK/PLK1 Dual Inhibitors with Quinazolinone as the Skeleton

Febrifugine is a kind of quinazolinone compound with high biological activity from a Chinese herb called Chang Shan (Dichroa febrifuga). Febrifugine and its derivatives possess extensive biological activities, some of which exhibited anti-tumor activities as FAK inhibitors. However, they are not very effective at inhibiting tumor metastasis, perhaps because tumors gain energy through compensatory activation of other signaling pathways that promote cell migration and invasion. Therefore, seventeen novel febrifugine derivatives with quinazolinone skeleton were designed, synthesized and acted as potential FAK/PLK1 dual inhibitors. These compounds were determined by ¹ H-NMR, ¹³ C-NMR and MS. Most of the compounds exhibited good inhibitory activity against cancer cell lines by computer-assisted screening, antitumor activity test and FAK/PLK1 inhibitory activity test, wherein compound 3b was screened as a high-efficiency lead compound.

Contribution of integrin adhesion to cytokinetic abscission and genomic integrity

Recent research shows that integrin-mediated adhesion contributes to the regulation of cell division at two key steps: the formation of the mitotic spindle at the mitotic entry and the final cytokinetic abscission at the mitotic exit. Failure in either of these processes will have a direct impact on the other in each round of the cell cycle and on the genomic integrity. This review aims to present how integrin signals are involved at these cell cycle stages under normal conditions and some safety mechanisms that may counteract the generation of aneuploid cells in cases of defective integrin signals.

Cell Cycle Regulation by Integrin-Mediated Adhesion

Cell cycle and cell adhesion are two interdependent cellular processes regulating each other, reciprocally, in every cell cycle phase. The cell adhesion to the extracellular matrix (ECM) via integrin receptors triggers signaling pathways required for the cell cycle progression; the passage from the G1 to S phase and the completion of cytokinesis are the best-understood events. Growing evidence, however, suggests more adhesion-dependent regulatory aspects of the cell cycle, particularly during G2 to M transition and early mitosis. Conversely, the cell cycle machinery regulates cell adhesion in manners recently shown driven mainly by cyclin-dependent kinase 1 (CDK1). This review summarizes the recent findings regarding the role of integrin-mediated cell adhesion and its downstream signaling components in regulating the cell cycle, emphasizing the cell cycle progression through the G2 and early M phases. Further investigations are required to raise our knowledge about the molecular mechanisms of crosstalk between cell adhesion and the cell cycle in detail.

Integrin-Mediated Adhesion Promotes Centrosome Separation in Early Mitosis

Integrin-mediated adhesion to the extracellular matrix is a key regulator of the cell cycle, as demonstrated for the passage of the G1/S checkpoint and the completion of cytokinetic abscission. Here, integrin-dependent regulation of the cell cycle in G2 and early M phases was investigated. The progression through the G2 and M phases was monitored by live-cell imaging and immunofluorescence staining in adherent and non-adherent fibroblast cells. Non-adherent cells, as well as adherent cells lacking FAK activity due to suppressed expression or pharmacological inhibition, exhibited a prolonged G2 phase and severely defect centrosome separation, resulting in delayed progress through the early mitotic stages. The activation of the critical mitotic regulator PLK1 and its indirect target Eg5, a kinesin-family motor protein driving the centrosome separation, were reduced in the cells lacking FAK activity. Furthermore, the absence of integrin adhesion or FAK activity destabilized the structural integrity of centrosomes and often caused detachment of pericentriolar material from the centrioles. These data identify a novel adhesion-dependent mechanism by which integrins via FAK and PLK1 contribute to the regulation of the cell cycle in the G2 and early M phases, and to the maintenance of genome integrity.

Mechanistic roles of tyrosine phosphorylation in reversible amyloids, autoinhibition, and endosomal membrane association of ALIX

Human apoptosis-linked gene-2 interacting protein X (ALIX), a versatile adapter protein, regulates essential cellular processes by shuttling between late endosomal membranes and the cytosol, determined by its interactions with Src kinase. Here, we investigate the molecular basis of these transitions and the effects of tyrosine phosphorylation on the interplay between structure, assembly, and intramolecular and intermolecular interactions of ALIX. As evidenced by transmission electron microscopy, fluorescence and circular dichroism spectroscopy, the proline-rich domain of ALIX, which encodes binding epitopes of multiple cellular partners, formed rope-like β-sheet–rich reversible amyloid fibrils that dissolved upon Src-mediated phosphorylation and were restored on protein-tyrosine phosphatase 1B–mediated dephosphorylation of its conserved tyrosine residues. Analyses of the Bro1 domain of ALIX by solution NMR spectroscopy elucidated the conformational changes originating from its phosphorylation by Src and established that Bro1 binds to hyperphosphorylated proline-rich domain and to analogs of late endosomal membranes via its highly basic surface. These results uncover the autoinhibition mechanism that relocates ALIX to the cytosol and the diverse roles played by tyrosine phosphorylation in cellular and membrane functions of ALIX.

[CEP55 may be a potential therapeutic target for non-obstructive azoospermia with maturation arrest]

OBJECTIVE

To explore the effect of small interfering RNA (siRNA)-mediated CEP55 gene silencing on the proliferation of mouse spermatogonia.

METHODS

Six patients with azoospermia diagnosed to have maturation arrest (3 cases) or normal spermatogenesis (3 cases) based on testicular biopsy between January 1 and December 31, 2017 in our center were examined for differential proteins in the testicular tissue using isobaric tags for relative and absolute quantitation (iTRAQ), and CEP55 was found to differentially expressed between the two groups of patients. We constructed a CEP55 siRNA for transfection in mouse spermatogonia and examined the inhibitory effects on CEP55 expressions using Western blotting and qPCR. The effect of CEP55 gene silencing on the proliferation of mouse spermatogonia was evaluated with CCK8 assay.

RESULTS

In the testicular tissues from the 6 patients with azoospermia, iTRAQ combined with LC/MS/MS analysis identified over two hundred differentially expressed proteins, among which CEP55 showed the most significant differential expression between the patients with maturation arrest and those with normal spermatogenesis. The cell transfection experiment showed that compared with the cells transfected with the vehicle or the negative control sequence, the mouse spermatogonia transfected with CEP55 siRNA showed significantly lowered expressions of CEP55 mRNA and protein (P < 0.05) and significantly decreased proliferation rate as shown by CCK8 assay (P < 0.05).

CONCLUSIONS

CEP55 may play a key role in spermatogenesis and may serve as a potential therapeutic target for non-obstructive azoospermia with maturation arrest.

Two NEMO-like Ubiquitin-Binding Domains in CEP55 Differently Regulate Cytokinesis

CEP55 regulates the final critical step of cell division termed cytokinetic abscission. We report herein that CEP55 contains two NEMO-like ubiquitin-binding domains (UBDs), NOA and ZF, which regulate its function in a different manner. In vitro studies of isolated domains showed that NOA adopts a dimeric coiled-coil structure, whereas ZF is based on a UBZ scaffold. Strikingly, CEP55 knocked-down HeLa cells reconstituted with the full-length CEP55 ubiquitin-binding defective mutants, containing structure-guided mutations either in NOA^CEP55 or ZF^CEP55 domains, display severe abscission defects. In addition, the ZF^CEP55 can be functionally replaced by some ZF-based UBDs belonging to the UBZ family, indicating that the essential function of ZF^CEP55 is to act as ubiquitin receptor. Our work reveals an unexpected role of CEP55 in non-degradative ubiquitin signaling during cytokinetic abscission and provides a molecular basis as to how CEP55 mutations can lead to neurological disorders such as the MARCH syndrome.

Traction forces at the cytokinetic ring regulate cell division and polyploidy in the migrating zebrafish epicardium

Epithelial repair and regeneration are driven by collective cell migration and division. Both cellular functions involve tightly controlled mechanical events, but how physical forces regulate cell division in migrating epithelia is largely unknown. Here we show that cells dividing in the migrating zebrafish epicardium exert large cell-extracellular matrix (ECM) forces during cytokinesis. These forces point towards the division axis and are exerted through focal adhesions that connect the cytokinetic ring to the underlying ECM. When subjected to high loading rates, these cytokinetic focal adhesions prevent closure of the contractile ring, leading to multi-nucleation through cytokinetic failure. By combining a clutch model with experiments on substrates of different rigidity, ECM composition and ligand density, we show that failed cytokinesis is triggered by adhesion reinforcement downstream of increased myosin density. The mechanical interaction between the cytokinetic ring and the ECM thus provides a mechanism for the regulation of cell division and polyploidy that may have implications in regeneration and cancer.

Septin and Ras regulate cytokinetic abscission in detached cells

Background

Integrin-mediated adhesion is normally required for cytokinetic abscission, and failure in the process can generate potentially oncogenic tetraploid cells. Here, detachment-induced formation of oncogenic tetraploid cells was analyzed in non-transformed human BJ fibroblasts and BJ expressing SV40LT (BJ-LT) ± overactive HRas.

Results

In contrast to BJ and BJ-LT cells, non-adherent BJ-LT-Ras cells recruited ALIX and CHMP4B to the midbody and divided. In detached BJ and BJ-LT cells regression of the cytokinetic furrow was suppressed by intercellular bridge-associated septin; after re-adhesion these cells divided by cytofission, however, some cells became bi-nucleated because of septin reorganization and furrow regression. Adherent bi-nucleated BJ cells became senescent in G1 with p21 accumulation in the nucleus, apparently due to p53 activation since adherent bi-nucleated BJ-LT cells passed through next cell cycle and divided into mono-nucleated tetraploids; the two centrosomes present in bi-nucleated BJ cells fused after furrow regression, pointing to the PIDDosome pathway as a possible mechanism for the p53 activation.

Conclusions

Several mechanisms prevent detached normal cells from generating tumor-causing tetraploid cells unless they have a suppressed p53 response by viruses, mutation or inflammation. Importantly, activating Ras mutations promote colony growth of detached transformed cells by inducing anchorage-independent cytokinetic abscission in single cells.

Connections between the cell cycle, cell adhesion and the cytoskeleton

Cell division, the purpose of which is to enable cell replication, and in particular to distribute complete, accurate copies of genetic material to daughter cells, is essential for the propagation of life. At a morphological level, division not only necessitates duplication of cellular structures, but it also relies on polar segregation of this material followed by physical scission of the parent cell. For these fundamental changes in cell shape and positioning to be achieved, mechanisms are required to link the cell cycle to the modulation of cytoarchitecture. Outside of mitosis, the three main cytoskeletal networks not only endow cells with a physical cytoplasmic skeleton, but they also provide a mechanism for spatio-temporal sensing via integrin-associated adhesion complexes and site-directed delivery of cargoes. During mitosis, some interphase functions are retained, but the architecture of the cytoskeleton changes dramatically, and there is a need to generate a mitotic spindle for chromosome segregation. An economical solution is to re-use existing cytoskeletal molecules: transcellular actin stress fibres remodel to create a rigid cortex and a cytokinetic furrow, while unipolar radial microtubules become the primary components of the bipolar spindle. This remodelling implies the existence of specific mechanisms that link the cell-cycle machinery to the control of adhesion and the cytoskeleton. In this article, we review the intimate three-way connection between microenvironmental sensing, adhesion signalling and cell proliferation, particularly in the contexts of normal growth control and aberrant tumour progression. As the morphological changes that occur during mitosis are ancient, the mechanisms linking the cell cycle to the cytoskeleton/adhesion signalling network are likely to be primordial in nature and we discuss recent advances that have elucidated elements of this link. A particular focus is the connection between CDK1 and cell adhesion. This article is part of a discussion meeting issue 'Forces in cancer: interdisciplinary approaches in tumour mechanobiology'.

Regulating a key mitotic regulator, polo-like kinase 1 (PLK1)

During cell division, duplicated genetic material is separated into two distinct daughter cells. This process is essential for initial tissue formation during development and to maintain tissue integrity throughout an organism's lifetime. To ensure the efficacy and efficiency of this process, the cell employs a variety of regulatory and signaling proteins that function as mitotic regulators and checkpoint proteins. One vital mitotic regulator is polo-like kinase 1 (PLK1), a highly conserved member of the polo-like kinase family. Unique from its paralogues, it functions specifically during mitosis as a regulator of cell division. PLK1 is spatially and temporally enriched at three distinct subcellular locales; the mitotic centrosomes, kinetochores, and the cytokinetic midbody. These localization patterns allow PLK1 to phosphorylate specific downstream targets to regulate mitosis. In this review, we will explore how polo-like kinases were originally discovered and diverged into the five paralogues (PLK1-5) in mammals. We will then focus specifically on the most conserved, PLK1, where we will discuss what is known about how its activity is modulated, its role during the cell cycle, and new, innovative tools that have been developed to examine its function and interactions in cells.

Src activation by Chk1 promotes actin patch formation and prevents chromatin bridge breakage in cytokinesis

In cytokinesis with chromatin bridges, cells delay abscission and retain actin patches at the intercellular canal to prevent chromosome breakage. In this study, we show that inhibition of Src, a protein-tyrosine kinase that regulates actin dynamics, or Chk1 kinase correlates with chromatin breakage and impaired formation of actin patches but not with abscission in the presence of chromatin bridges. Chk1 is required for optimal localization and complete activation of Src. Furthermore, Chk1 phosphorylates human Src at serine 51, and phosphorylated Src localizes to actin patches, the cell membrane, or the nucleus. Nonphosphorylatable mutation of S51 to alanine reduces Src catalytic activity and impairs formation of actin patches, whereas expression of a phosphomimicking Src-S51D protein rescues actin patches and prevents chromatin breakage in Chk1-deficient cells. We propose that Chk1 phosphorylates Src-S51 to fully induce Src kinase activity and that phosphorylated Src promotes formation of actin patches and stabilizes chromatin bridges. These results identify proteins that regulate formation of actin patches in cytokinesis.

MicroRNA-144-3p inhibits cell proliferation and induces cell apoptosis in prostate cancer by targeting CEP55

Previous research reported that miR-144-3p functions as tumor suppressor in several tumors, including glioblastoma and hepatocelluar carcinoma, but the role of miR-144-3p in prostate cancer (PCa) remains unclear. In this study, we aimed to analyze the role of miR-144-3p in PCa. By RT-qPCR, we found that expression of miR-144-3p was markedly down-regulated in PCa tissues and cell lines compared with that in paired adjacent normal tissues and normal cell lines. Moreover, miR-144-3p overexpression in PC-3 and DU145 cells by transfection with miR-144-3p mimics significantly inhibited cell proliferation and in vitro by MTT, colony formation assays and suppressed tumor growth in vivo by nude mice model. Flow cytometry analysis further demonstrated that forced expression of miR-144-3p induced cell cycle G1/S phase arrest and apoptosis. Moreover, centrosomal protein of 55 (CEP55) was confirmed as a direct target of miR-144-3p by bioinformatics analysis and luciferase reporter assays. Overexpression of miR-144-3p decreased the CEP5 mRNA and protein levels in PC-3 and DU145 cells. Using Oncomine database analysis, we further found the expression of CEP55 was significantly upregulated in PCa tissues. In addition, knockdown of CEP55 elicited similar effects with miR-144-3p overexpression in PCa cells. Taken together, our results demonstrate that miR-144-3p functions as a tumor suppressor in PCa by downregulating CEP55, supporting the targeting miR-144-3p might be a potentially effective therapeutic approach for PCa.

Cell-intrinsic and -extrinsic mechanisms promote cell-type-specific cytokinetic diversity

Cytokinesis, the physical division of one cell into two, is powered by constriction of an actomyosin contractile ring. It has long been assumed that all animal cells divide by a similar molecular mechanism, but growing evidence suggests that cytokinetic regulation in individual cell types has more variation than previously realized. In the four-cell Caenorhabditis elegans embryo, each blastomere has a distinct cell fate, specified by conserved pathways. Using fast-acting temperature-sensitive mutants and acute drug treatment, we identified cell-type-specific variation in the cytokinetic requirement for a robust formin^CYK-1-dependent filamentous-actin (F-actin) cytoskeleton. In one cell (P2), this cytokinetic variation is cell-intrinsically regulated, whereas in another cell (EMS) this variation is cell-extrinsically regulated, dependent on both Src^SRC-1 signaling and direct contact with its neighbor cell, P2. Thus, both cell-intrinsic and -extrinsic mechanisms control cytokinetic variation in individual cell types and can protect against division failure when the contractile ring is weakened.

The successful division of one cell into two is essential for all organisms to live, grow and reproduce. For an animal cell, the nucleus – the compartment containing the genetic material – must divide before the surrounding material. The rest of the cell, called the cytoplasm, physically separates later in a process known as cytokinesis.

Cytokinesis in animal cells is driven by the formation of a ring in the middle of the dividing cell. The ring is composed of myosin motor proteins and filaments made of a protein called actin. The movements of the motor proteins along the filaments cause the ring to contract and tighten. This pulls the cell membrane inward and physically pinches the cell into two. For a long time, the mechanism of cytokinesis was assumed to be same across different types of animal cell, but later evidence suggested otherwise. For example, in liver, heat and bone cells, cytokinesis naturally fails during development to create cells with two or more nuclei. If a similar ‘failure’ happened in other cell types, it could lead to diseases such as cancers or blood disorders. This raised the question: what are the molecular mechanisms that allow cytokinesis to happen differently in different cell types?

Davies et al. investigated this question using embryos of the worm Caenorhabditis elegans at a stage in their development when they consist of just four cells. The proteins forming the contractile ring in this worm are the same as those in humans. However, in the worm, the contractile ring can easily be damaged using chemical inhibitors or by mutating the genes that encode its proteins.

Davies et al. show that when the contractile ring was damaged, two of the four cells in the worm embryo still divided successfully. This result indicates the existence of new mechanisms to divide the cytoplasm that allow division even with a weak contractile ring. In a further experiment, the embryos were dissected to isolate each of the four cells. Davies et al. saw that one of the two dividing cells could still divide on its own, while the other cell could not. This shows that this new method of cytokinesis is regulated both by factors inherent to the dividing cell and by external signals from other cells. Moreover, one of these extrinsic signals was found to be a signaling protein that had previously been implicated in human cancers.

Future work will determine if these variations in cytokinesis between the different cell types found in the worm apply to humans too; and, more importantly from a therapeutic standpoint, if these new mechanisms exist in human cancers.

Prognostic significance of Cep55 in oral squamous cell carcinoma

Objective:

Currently, oral squamous cell carcinoma (OSCC) is one of the most fatal cancers of all head and neck malignancies. Despite advancements in therapy, the mortality and morbidity remain high. Hence, it is essential to identify useful prognostic markers for high-risk individuals with OSCC to decide on treatment protocols. Centrosomal protein 55 ( Cep55), a regulator of the cell cycle, has been considered to play a role in carcinogenesis. Although there are numerous studies on its role in various other epithelial cancers such as breast, ovarian and lung cancers, its significance in the behaviour of OSCC is yet to be studied. The present study aimed to study Cep55 expression in OSCC and correlate with the tumour characteristics and patient survival.

Materials and Methods:

Forty pathologically diagnosed cases of OSCC were included in the study: 20 each of early and advanced OSCC cases. Formalin-fixed paraffin-embedded archival samples were used. The sections were immunohistochemically stained with Cep55 antibody. The expression levels of Cep55 were correlated with clinical parameters and disease outcome.

Results:

A higher expression of Cep55 was observed in advanced stage compared to early stage of OSCC. The Cep55 expression showed no significant relation with respect to clinical staging, pathological grading and site, except for tongue. Cep55 overexpression is significantly associated with poor survival.

Conclusion:

The present study suggests that Cep55 could play an important role in determining the biological behaviour and survival of OSCC patients independent of tumour staging and pathological grading. Thus, assessment of Cep55 expression could navigate the surgeons to plan an appropriate treatment.

Targeting forkhead box M1 transcription factor in breast cancer

Breast cancer continues to be the most commonly diagnosed malignancy and second most common cause of cancer-related deaths among women in the United States. Improved understanding of the molecular heterogeneity of breast tumors and the approval of multiple targeted therapies have revolutionized the treatment landscape and long-term survival rates for patients with breast cancer. Despite the development of highly effective targeted agents, drug resistance and disease progression remain major clinical concerns. Improved understanding of the molecular mechanisms mediating drug resistance will allow new treatments to be developed. The forkhead box M1 (FoxM1) transcription factor is overexpressed in breast cancer and strongly associated with resistance to targeted therapies and chemotherapy. FoxM1 regulates all hallmarks of cancer, including proliferation, mitosis, EMT, invasion, and metastasis. Inhibition of FoxM1 transcription factor function is a potential strategy for overcoming breast cancer progression. In this research update, we review the role of FoxM1 in breast cancer and pharmacological approaches for blocking FoxM1 transcription factor function. Future preclinical studies should evaluate combination drug strategies to inhibit FoxM1 function and upstream kinase signaling pathways as potential strategies to treat resistant and metastatic breast cancers.

Tension-induced cytokinetic abscission in human fibroblasts

Previous studies have shown that cytokinetic abscission at the end of mitosis is executed by the ESCRT machinery in mammalian cells, and that the process is dependent on adhesion-induced integrin signalling via a FAK-PLK1-CEP55-TSG101/Alix-CHMP4B pathway. The present study identified an alternative abscission mechanism driven by mechanical force. In the absence of integrin signals (non-adherent conditions), cytokinesis in non-transformed human fibroblasts proceeds to CEP55 accumulation at the midbody, but after prolonged time (>3 hours) the major midbody components Aurora B, MKLP1 and CEP55 were no longer detected in the area. Upon adhesion to fibronectin, such cells were able to complete abscission without re-appearance of midbody proteins. Live-cell imaging revealed that re-plating on stiff fibronectin matrix (64 KPa) allowed >95% of the cells to complete abscission within 9 hours while the corresponding number was 40% on soft fibronectin matrix (0.5 KPa). The cells re-plated on poly-L-lysine were not able to generate tension and did not divide. Thus, mechanical tension can cause cytokinetic abscission by stretching of the intercellular bridge between the two daughter cells until it eventually ruptures without the involvement of ESCRT complexes. Importantly, regression of the cleavage furrow and formation of bi-nucleated cells did not occur in most of the suspension-treated mitotic cells after re-plating on fibronectin. Septin, which stabilizes the membrane associated with the midbody, was found to remain along the ingressed membrane, suggesting that this filament system maintains the membrane bridge although the midbody had dissolved, thereby preventing regression and allowing tension to act on the narrow intercellular bridge.

Involvement of PUMA in pericyte migration induced by methamphetamine

Mounting evidence indicates that methamphetamine causes blood-brain barrier damage, with emphasis on endothelial cells. The role of pericytes in methamphetamine-induced BBB damage remains unknown. Our study demonstrated that methamphetamine increased the migration of pericytes from the endothelial basement membrane. However, the detailed mechanisms underlying this process remain poorly understood. Thus, we examined the molecular mechanisms involved in methamphetamine-induced pericyte migration. The results showed that exposure of C3H/10T1/2 cells and HBVPs to methamphetamine increased PUMA expression via activation of the sigma-1 receptor, MAPK and Akt/PI3K pathways. Moreover, methamphetamine treatment resulted in the increased migration of C3H/10T1/2 cells and HBVPs. Knockdown of PUMA in pericytes transduced with PUMA siRNA attenuated the methamphetamine-induced increase in cell migration through attenuation of integrin and tyrosine kinase mechanisms, implicating a role of PUMA in the migration of C3H/10T1/2 cells and HBVPs. This study has demonstrated that methamphetamine-mediated pericytes migration involves PUMA up-regulation. Thus, targeted studies of PUMA could provide insights to facilitate the development of a potential therapeutic approach for alleviation of methamphetamine-induced pericyte migration.