Microtubule disruption in keratinocytes induces cell-cell adhesion through activation of endogenous E-cadherin

Electrotaxis evokes directional separation of co-cultured keratinocytes and fibroblasts

Bioelectric communication plays a significant role in several cellular processes and biological mechanisms, such as division, differentiation, migration, cancer metastasis, and wound healing. Ion flow across cellular walls leads to potential gradients and subsequent formation of constant or time-varying electric fields(EFs), which regulate cellular processes. An EF is natively generated towards the wound center during epithelial wound healing, aiming to align and guide cell migration, particularly of macrophages, fibroblasts, and keratinocytes. While this phenomenon, known as electrotaxis or galvanotaxis, has been extensively investigated across many cell types, it is typically explored one cell type at a time, which does not accurately represent cellular interactions during complex biological processes. Here we show the co-cultured electrotaxis of epidermal keratinocytes and dermal fibroblasts with a salt-bridgeless microfluidic approach for the first time. The electrotactic response of these cells was first assessed in mono-culture to establish a baseline, resulting in the characteristic cathodic migration for keratinocytes and anodic for fibroblasts. Both cell types retained their electrotactic properties in co-culture leading to clear cellular partition even in the presence of cellular collisions. The methods leveraged here pave the way for future co-culture electrotaxis experiments where the concurrent influence of cell types can be thoroughly investigated.

Hemidesmosome-Related Keratin Filament Bundling and Nucleation

The epithelial cytoskeleton encompasses actin filaments, microtubules, and keratin intermediate filaments. They are interconnected and attached to the extracellular matrix via focal adhesions and hemidesmosomes. To study their interplay, we inhibited actin and tubulin polymerization in the human keratinocyte cell line HaCaT by latrunculin B and nocodazole, respectively. Using immunocytochemistry and time-lapse imaging of living cells, we found that inhibition of actin and tubulin polymerization alone or in combination induced keratin network re-organization albeit differently in each situation. Keratin filament network retraction towards the nucleus and formation of bundled and radial keratin filaments was most pronounced in latrunculin-B treated cells but less in doubly-treated cells and not detectable in the presence of nocodazole alone. Hemidesmosomal keratin filament anchorage was maintained in each instance, whereas focal adhesions were disassembled in the absence of actin filaments. Simultaneous inhibition of actin and tubulin polymerization, therefore, allowed us to dissect hemidesmosome-specific functions for keratin network properties. These included not only anchorage of keratin filament bundles but also nucleation of keratin filaments, which was also observed in migrating cells. The findings highlight the fundamental role of hemidesmosomal adhesion for keratin network formation and organization independent of other cytoskeletal filaments pointing to a unique mechanobiological function.

PI3 Kinase Pathway and MET Inhibition is Efficacious in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive cancer that is commonly associated with prior asbestos exposure. Receptor tyrosine kinases (RTKs) such as MET and its downstream target PI3K are overexpressed and activated in a majority of MPMs. Here, we studied the combinatorial therapeutic efficacy of the MET/ALK inhibitor crizotinib, with either a pan-class I PI3K inhibitor, BKM120, or with a PI3K/mTOR dual inhibitor, GDC-0980, in mesothelioma. Cell viability results showed that MPM cells were highly sensitive to crizotinib, BKM120 and GDC-0980 when used individually and their combination was more effective in suppressing growth. Treatment of MPM cells with these inhibitors also significantly decreased cell migration, and the combination of them was synergistic. Treatment with BKM120 alone or in combination with crizotinib induced G2-M arrest and apoptosis. Both crizotinib and BKM120 strongly inhibited the activity of MET and PI3K as evidenced by the decreased phosphorylation of MET, AKT and ribosomal S6 kinase. Using a PDX mouse model, we showed that a combination of crizotinib with BKM120 was highly synergetic in inhibiting MPM tumor growth. In conclusion our findings suggest that dual inhibition of PI3K and MET pathway is an effective strategy in treating MPM as compared to a single agent.

Stathmin destabilizing microtubule dynamics promotes malignant potential in cancer cells by epithelial-mesenchymal transition

BACKGROUND

Stathmin is a ubiquitous cytosolic regulatory phosphoprotein and is overexpressed in different human malignancies. The main physiological function of stathmin is to interfere with microtubule dynamics by promoting depolymerization of microtubules or by preventing polymerization of tubulin heterodimers. Stathmin plays important roles in regulating many cellular functions as a result of its microtubule-destabilizing activity. Currently, the critical roles of stathmin in cancer cells, as well as in lymphocytes have been valued. This review discusses stathmin and microtubule dynamics in cancer development, and hypothesizes their possible relationship with epithelial-mesenchymal transition (EMT).

DATA SOURCES

A PubMed search using such terms as "stathmin", "microtubule dynamics", "epithelial-mesenchymal transition", "EMT", "malignant potential" and "cancer" was performed to identify relevant studies published in English. More than 100 related articles were reviewed.

RESULTS

The literature clearly documented the relationship between stathmin and its microtubule-destabilizing activity of cancer development. However, the particular mechanism is poorly understood. Microtubule disruption is essential for EMT, which is a crucial process during cancer development. As a microtubule-destabilizing protein, stathmin may promote malignant potential in cancer cells by initiating EMT.

CONCLUSIONS

We propose that there is a stathmin-microtubule dynamics-EMT (S-M-E) axis during cancer development. By this axis, stathmin together with its microtubule-destabilizing activity contributes to EMT, which stimulates the malignant potential in cancer cells.

Adhesive interactions of N-cadherin limit the recruitment of microtubules to cell–cell contacts through organization of actomyosin

Adhesive interactions of cadherins induce crosstalk between adhesion complexes and the actin cytoskeleton, allowing strengthening of adhesions and cytoskeletal organization. The underlying mechanisms are not completely understood, and microtubules (MTs) might be involved, as for integrin-mediated cell–extracellular-matrix adhesions. Therefore, we investigated the relationship between N-cadherin and MTs by analyzing the influence of N-cadherin engagement on MT distribution and dynamics. MTs progressed less, with a lower elongation rate, towards cadherin adhesions than towards focal adhesions. Increased actin treadmilling and the presence of an actomyosin contractile belt, suggested that actin relays inhibitory signals from cadherin adhesions to MTs. The reduced rate of MT elongation, associated with reduced recruitment of end-binding (EB) proteins to plus ends, was alleviated by expression of truncated N-cadherin, but was only moderately affected when actomyosin was disrupted. By contrast, destabilizing actomyosin fibers allowed MTs to enter the adhesion area, suggesting that tangential actin bundles impede MT growth independently of MT dynamics. Blocking MT penetration into the adhesion area strengthened cadherin adhesions. Taken together, these results establish a crosstalk between N-cadherin, F-actin and MTs. The opposing effects of cadherin and integrin engagement on actin organization and MT distribution might induce bias of the MT network during cell polarization.

CLASP2 interacts with p120-catenin and governs microtubule dynamics at adherens junctions

The microtubule plus end–binding protein CLASP2 localizes to adherens junctions via direct interaction with p120-catenin and is required for adherens junction stability.

Classical cadherins and their connections with microtubules (MTs) are emerging as important determinants of cell adhesion. However, the functional relevance of such interactions and the molecular players that contribute to tissue architecture are still emerging. In this paper, we report that the MT plus end–binding protein CLASP2 localizes to adherens junctions (AJs) via direct interaction with p120-catenin (p120) in primary basal mouse keratinocytes. Reductions in the levels of p120 or CLASP2 decreased the localization of the other protein to cell–cell contacts and altered AJ dynamics and stability. These features were accompanied by decreased MT density and altered MT dynamics at intercellular junction sites. Interestingly, CLASP2 was enriched at the cortex of basal progenitor keratinocytes, in close localization to p120. Our findings suggest the existence of a new mechanism of MT targeting to AJs with potential functional implications in the maintenance of proper cell–cell adhesion in epidermal stem cells.

Noncentrosomal microtubules and type II myosins potentiate epidermal cell adhesion and barrier formation

Noncentrosomal microtubules recruit myosin II to the cell cortex in order to engage adherens junctions and increase tight junction formation, resulting in an increase in mechanical integrity of cell sheets.

During differentiation, many cells reorganize their microtubule cytoskeleton into noncentrosomal arrays. Although these microtubules are likely organized to meet the physiological roles of their tissues, their functions in most cell types remain unexplored. In the epidermis, differentiation induces the reorganization of microtubules to cell–cell junctions in a desmosome-dependent manner. Here, we recapitulate the reorganization of microtubules in cultured epidermal cells. Using this reorganization assay, we show that cortical microtubules recruit myosin II to the cell cortex in order to engage adherens junctions, resulting in an increase in mechanical integrity of the cell sheets. Cortical microtubules and engaged adherens junctions, in turn, increase tight junction function. In vivo, disruption of microtubules or loss of myosin IIA and B resulted in loss of tight junction–mediated barrier activity. We propose that noncentrosomal microtubules act through myosin II recruitment to potentiate cell adhesion in the differentiating epidermis, thus forming a robust mechanical and chemical barrier against the external environment.

The biomechanical properties of 3d extracellular matrices and embedded cells regulate the invasiveness of cancer cells

The malignancy of tumors depends on the biomechanical properties of cancer cells and their microenvironment, which enable cancer cells to migrate through the connective tissue, transmigrate through basement membranes and endothelial monolayers and form metastases in targeted organs. The current focus of cancer research is still based on biological capabilities such as molecular genetics and gene signaling, but these approaches ignore the mechanical nature of the invasion process of cancer cells. This review will focus on how structural, biochemical and mechanical properties of extracellular matrices (ECMs), and adjacent cells regulate the invasiveness of cancer cells. In addition, it presents how cancer cells create their own microenvironment by restructuring of the ECM and by interaction with stromal cells, which then further contribute to the progression of cancer disease. Finally, this review will point out that mechanical properties are a critical determinant for the efficiency of cancer cell invasion and the progression of cancer which might affect the future development of new cancer treatments.

KazrinE is a desmosome-associated liprin that colocalises with acetylated microtubules

Kazrin is a widely expressed, evolutionarily conserved cytoplasmic protein that binds the cytolinker protein periplakin. Multiple functions of kazrin have been reported, including regulation of desmosome assembly, embryonic tissue morphogenesis and epidermal differentiation. Here, we identify kazrinE as a kazrin isoform that contains a liprin-homology domain (LHD) and forms complexes with kazrinA, kazrinB and kazrinC. As predicted from the presence of the LHD, kazrinE can associate with the leukocyte common antigen-related (LAR) protein tyrosine phosphatase in a phosphorylation-dependent manner. When overexpressed in epidermal keratinocytes, kazrinE induces changes in cell shape and stimulates terminal differentiation. Like the other kazrin isoforms, kazrinE localises to the nucleus and desmosomes. However, in addition, kazrinE associates with stabilised microtubules via its LHD. During terminal differentiation, the keratinocyte microtubule network undergoes extensive reorganisation; in differentiating keratinocytes, endogenous kazrinE colocalises with microtubules, but periplakin does not. We speculate that the kazrinE-microtubule interaction contributes to the mechanism by which kazrin regulates desmosome formation and epidermal differentiation.

Integrin beta3 down-regulates invasive features of ovarian cancer cells in SKOV3 cell subclones

PURPOSE

To investigate the role of integrin beta3 in invasive features of ovarian cancer SKOV3 cells, by comparing different metastatic subclones.

METHODS

In the present study, two cell subclones, termed as S1 and S21, which possessed high and low metastatic potential, respectively, were isolated and established from human ovarian cancer parental cell line SKOV3 by the limited dilution method. The expressions of integrin alphav, integrin alphavbeta3, integrin beta3, E-cadherin, FAK and ILK in the two cell subclones were compared by means of real-time RT-PCR or flow cytometry. Subsequently, S21 was transfected with siRNA for integrin beta3 and the effects of transfection were examined by methyl thiazolyl tetrazolium (MTT) assay, colony formation assay, Matrigel invasion assay and cell migration assay.

RESULTS

The expressions of integrin alphavbeta3, integrin beta3 and E-cadherin were markedly down-regulated in S1; however, there were no significant differences in the expressions of integrin alphav, FAK and ILK beta. Of note, more than 70% knockdown of integrin beta3 expression was obtained by siRNA technique. The integrin beta3-siRNA-transfected cells showed significant increases in cell proliferation, cell migration and invasive activity in contrast with the mock-transfected cells. The expressions of integrin alphavbeta3 and E-cadherin were lower in the integrin beta3-siRNA-transfected cells compared to the mock control.

CONCLUSION

Integrin beta3, like E-cadherin, may be also a suppressor gene down-regulating invasive features of ovarian cancer cells in SKOV3 cell subclones.

Building epithelial tissues from skin stem cells

The skin epidermis and its appendages provide a protective barrier that guards against loss of fluids, physical trauma, and invasion by harmful microbes. To perform these functions while confronting the harsh environs of the outside world, our body surface undergoes constant rejuvenation through homeostasis. In addition, it must be primed to repair wounds in response to injury. The adult skin maintains epidermal homeostasis, hair regeneration, and wound repair through the use of its stem cells. What are the properties of skin stem cells, when do they become established during embryogenesis, and how are they able to build tissues with such remarkably distinct architectures? How do stem cells maintain tissue homeostasis and repair wounds and how do they regulate the delicate balance between proliferation and differentiation? What is the relationship between skin cancer and mutations that perturbs the regulation of stem cells? In the past 5 years, the field of skin stem cells has bloomed as we and others have been able to purify and dissect the molecular properties of these tiny reservoirs of goliath potential. We report here progress on these fronts, with emphasis on our laboratory's contributions to the fascinating world of skin stem cells.

Areca nut extract represses migration and differentiation while activating matrix metalloproteinase-9 of normal gingival epithelial cells

BACKGROUND AND OBJECTIVE

Areca (betel) chewing is associated with an increase in the incidence of periodontal diseases. Aberrations in matrix metalloproteinase (MMP) expression have been reported to be associated with periodontal disease. This study investigated the effects of areca nut extract on MMP activity and the phenotype of human gingival epithelial cells.

MATERIAL AND METHODS

Reverse transcription-polymerase chain reaction, western blotting and gelatin zymography were used to assay MMPs. Cell viability, mobility and detachment assays were performed to characterize the phenotypic impact. Confocal microscopy was employed to evaluate cell aggregation and the distribution of E-cadherin and F-actin.

RESULTS

Treatment of gingival epithelial cells with 10 microg/mL of areca nut extract reduced its cell viability. Treatment with 5 and 10 microg/mL of areca nut extract for 24 h activated MMP-9 but not MMP-2 in gingival epithelial cells. This activation could be nuclear factor-kappaB dependent and was abrogated by 10 microM curcumin. Areca nut extract also reduced the migration and detachment of gingival epithelial cells. The differentiated cell-cell contact of gingival epithelial cells was markedly impaired by areca nut extract. This was accompanied by a disruption of distribution of E-cadherin and F-actin.

CONCLUSION

The areca nut extract-mediated activation of MMP-9 in gingival epithelial cells could signify a potential periodontal pathogenesis in areca chewers. The areca nut extract-mediated inhibition of cell viability and migration, together with the changed aggregation in gingival epithelial cells, suggests that impairment of the re-epithelization underlies the process and this, in turn, might exacerbate gingival inflammation.

Stem cells, phenotypic inversion, and differentiation

Stem cells possess the potential to cure a myriad of ailments ranging from congenital diseases to illnesses acquired through the physiological process of aging. In the adult, these cells are extremely rare and often difficult to isolate in numbers sufficient to apply to medical treatment. Ex vivo expansion of these cells will be required for most meaningful interventions. The discovery of stem/progenitor cell inversion offers a new avenue for obtaining sufficient numbers of stem cells. Adult progenitor cells are much more common than quiescent stem cells and can be isolated with minimal interventions; therefore, inversion of progenitors to stem cells may become a feasible approach for therapeutic purposes. Stem cells are known to possess few mitochondria, and mitochondrial biogenesis is required for stem cell differentiation. The microtubule cytoskeleton is a major regulator for mitochondrial biogenesis. Investigations in the area of controlling cell differentiation and inducing phenotypic inversion, possibly through manipulation of mitochondrial biogenesis, may contribute to stem cell-based therapies.

Microtubule dynamics and Rac-1 signaling independently regulate barrier function in lung epithelial cells

Cadherin-mediated cell-cell adhesion controls the morphology and function of epithelial cells and is a critical component of the pathology of chronic inflammatory disorders. Dynamic interactions between cadherins and the actin cytoskeleton are required for stable cell-cell contact. Besides actin, microtubules also target intercellular, cadherin-based junctions and contribute to their formation and stability. Here, we studied the role of microtubules in conjunction with Rho-like GTPases in the regulation of lung epithelial barrier function using real-time monitoring of transepithelial electrical resistance. Unexpectedly, we found that disruption of microtubules promotes epithelial cell-cell adhesion. This increase in epithelial barrier function is accompanied by the accumulation of beta-catenin at cell-cell junctions, as detected by immunofluorescence. Moreover, we found that the increase in cell-cell contact, induced by microtubule depolymerization, requires signaling through a RhoA/Rho kinase pathway. The Rac-1 GTPase counteracts this pathway, because inhibition of Rac-1 signaling rapidly promotes epithelial barrier function, in a microtubule- and RhoA-independent fashion. Together, our data suggest that microtubule-RhoA-mediated signaling and Rac-1 control lung epithelial integrity through counteracting independent pathways.

Expression of E-cadherin in cervical lymph nodes from primary oral squamous cell carcinoma patients

BACKGROUND

Oral squamous cell carcinoma (OSCC) is the most common malignant tumor in oral and maxillofacial region with poor prognosis. E-cadherin plays a key role in cell-to-cell adhesion. E-cadherin expression in the metastatic cervical lymph node, especially in the micrometastatic cervical lymph node has seldom been reported in OSCC patients.

OBJECTIVE

To investigate the E-cadherin expression in cervical lymph nodes from OSCC patients as well as its clinical significance.

DESIGN

Thirty-three OSCC patients were involved in this study; among them, there were 28 males and 5 females, the age ranged from 34 to 78 years (mean 58.8 years). The most suspicious metastatic cervical lymph node (total 99 lymph nodes) from three cervical regions of each OSCC patient was selected for detection of E-cadherin using routine pathological examination and immunohistochemistry.

RESULTS

Increased E-cadherin expression in the metastatic cervical lymph nodes was detected, which was diagnosed by routine pathological examination using HE staining. However, in the micrometastatic cervical lymph node, E-cadherin expression was negative. The survival rate of OSCC patients correlated with decreased E-cadherin expression (P=0.001), N stage (P=0.024) and tumor recurrence (P<0.001). Tumor recurrence is the only independent factor on the prognosis (RR=20.83 and P=0.014).

CONCLUSIONS

Decreased E-cadherin expression in cancerous tissue correlates with the poor prognosis of OSCC patients. Detection of E-cadherin expression is useful to confirm the cervical lymph node metastasis and maybe useless to detect the cervical lymph node micrometastasis; further studies are encouraged to reveal the detail mechanism of E-cadherin expression in formation of lymph node metastatic focus.

Upregulation of class II beta-tubulin expression in differentiating keratinocytes

The diverse functions of microtubules (MT) in different cells and tissues may be facilitated by compositional changes in tubulin isotypes. We obtained partial cDNA clones of class II beta-tubulin from a library of differentiating normal human epidermal keratinocytes (NHEK) cells, whereas screening via subtractive hybridization for genes involved in calcium-induced keratinocyte differentiation. Analysis of the isotypic composition of beta-tubulin from NHEK cells revealed elevations in class II beta-tubulin concentrations at both protein and message levels during cell differentiation, resulting in increased rates of incorporation of class II beta-tubulin into MT. Immunohistochemistry of normal and pathologic skin tissues showed that class II beta-tubulin occurred in the granular layer of the epidermis and in differentiated areas of carcinomas. Class II beta-tubulin was, however, not observed in the uppermost granular and cornified layers of normal epidermis. Further experiments showed that MT were likely to decay in the final stage of terminal differentiation during formation of the cornified envelope. Our results suggest that there is differential modulation of MT composition and stability during keratinocyte differentiation.

Motility of endodermal epithelial cells plays a major role in reorganizing the two epithelial layers in Hydra

Cell-cell interactions and cell rearrangements play important roles during development. Aggregates of Hydra cells reorganize into the two epithelial layers and subsequently form a normal animal. Examination of the formation of the two layers under various situations, indicates that the motility of endodermal epithelial cells, but not the differential adhesive forces of the two types of epithelial cells, plays the critical role in setting up the two epithelial layers. (1) When aggregates of ectodermal cells and of endodermal cells were placed in direct contact, the endodermal cells migrated into the interior of the ectodermal aggregate. This process was completely inhibited by cytochalasin B although initial firm attachment between the two aggregates was not blocked. (2) A single endodermal epithelial cell placed in contact with an ectodermal aggregate, actively extended pseudopod-like structures and migrated toward the center of the ectodermal aggregate. In contrast, an ectodermal epithelial cell remained in contact with an endodermal aggregate and never exhibited migratory behavior. Cytochalasin treatment of only endodermal epithelial cells abolished the migration. (3) One to 4 endodermal epithelial cells and/or ectodermal epithelial cells were placed in contact with one another forming up to 4-cell aggregates. Endodermal epithelial cells exhibited high motility that can be attributed to the migratory movement described above. Finally, formation of actin bundles, as visualized with rhodamine-phalloidin, was always correlated with pseudopod formation in endodermal epithelial cells during early and mid stages of aggregate formation.

Epithelial barrier function: assembly and structural features of the cornified cell envelope

Terminally differentiating stratified squamous epithelial cells assemble a specialized protective barrier structure on their periphery termed the cornified cell envelope (CE). It is composed of numerous structural proteins that become cross-linked by several transglutaminase enzymes into an insoluble macromolecular assembly. Several proteins are involved in the initial stages of CE assembly, but only certain proteins from a choice of more than 20 different proteins are used in the final stages of CE reinforcement, apparently to meet tissue-specific requirements. In addition, a variable selection of proteins may be upregulated in response to genetic defects of one of the CE proteins or tissue injury, in an effort to maintain an effective barrier. Additionally, in the epidermis and hair fiber cuticle, a layer of lipids is covalently attached to the proteins, which provides essential water barrier properties. Here we describe our current understanding of CE structure, a possible mechanism of its assembly, and various disorders that cause a defective barrier.

Cell-cell adhesion and RhoA-mediated actin polymerization are independent phenomena in microtubule disrupted keratinocytes

E-cadherin-mediated adherens junction formation and maintenance are thought to involve actin filament rearrangements through the action of small GTPases. Recently, we demonstrated that microtubule disruption in normal human epidermal keratinocytes grown in low calcium media conditions induces cell-cell adhesion by redistribution of endogenous E-cadherin, and it promotes stress fiber formation. This actin rearrangement was apparently mediated by RhoA activation. This model system therefore provides a tool with which to dissect relationships between cell-cell adhesion and Rho-mediated stress fiber formation. In this study, we have demonstrated in normal human epidermal keratinocytes that disruption of actin structures including stress fibers does not interfere with E-cadherin redistribution during microtubule-induced cell-cell adhesion. Moreover, this cell-cell adhesion could not be blocked by RhoA inactivation at the level for inhibition of stress fiber formation. Additionally, in the immortalized HaCaT keratinocyte cell line, which does not undergo cell-cell adhesion after microtubule disruption in low calcium conditions, expression of dominant-active RhoA could induce stress fiber formation without inducing adhesion. On the other hand, a variant of the HaCaT cell line, HC-R1, showed microtubule-disruption-induced cell-cell adhesion without stress fiber formation. Together, our results suggest that, in keratinocytes, the process of cell adhesion can occur independently of RhoA-mediated stress fiber formation.