p38δ mitogen-activated protein kinase regulates the expression of tight junction protein ZO-1 in differentiating human epidermal keratinocytes

JNK inhibition enhances cell-cell adhesion impaired by desmoglein 3 gene disruption in keratinocytes

c-Jun NH2-terminal protein kinase (JNK) and p38 are stress-activated mitogen-activated protein kinases (MAPK) that are phosphorylated by various stimuli. It has been reported that the loss of desmoglein (DSG) 3, a desmosomal transmembrane core molecule, in keratinocytes impairs cell-cell adhesion accompanied by p38 MAPK activation. To understand the biological role of DSG3 in desmosomes and its relationship with stress-activated MAPKs, we established DSG3 knockout keratinocytes (KO cells). Wild-type cells showed a linear localization of DSG1 to cell-cell contacts, whereas KO cells showed a remarkable reduction despite the increased protein levels of DSG1. Cell-cell adhesion in KO cells was impaired over time, as demonstrated by dispase-based dissociation assays. The linear localization of DSG1 to cell-cell contacts and the strength of cell-cell adhesion were promoted by the pharmacological inhibition of JNK. Conversely, pharmacological activation of JNK, but not p38 MAPK, in wild-type cells reduced the linear localization of DSG1 in cell-cell contacts. Our data indicate that DSG1 and DSG2 in KO cells cannot compensate for the attenuation of cell-cell adhesion strength caused by DSG3 deficiency and that JNK inhibition restores the strength of cell-cell adhesion by increasing the linear localization of DSG1 in cell-cell contacts in KO cells. Inhibition of JNK signaling may improve cell-cell adhesion in diseases in which DSG3 expression is impaired.

Modulation of Bovine Endometrial Cell Receptors and Signaling Pathways as a Nanotherapeutic Exploration against Dairy Cow Postpartum Endometritis

Simple Summary

The provision of updated information on the molecular pathogenesis of bovine endometritis with host-pathogen interactions and the possibility of exploring the cellular sensors mechanism in a nanotechnology-based drug delivery system against persistent endometritis were reported in this review. The mechanism of Gram-negative bacteria and their ligands has been vividly explored, with the paucity of research detail on Gram-positive bacteria in bovine endometritis. The function of cell receptors, biomolecules proteins, and sensors were reportedly essential in transferring signals into cell signaling pathways to induce immuno-inflammatory responses by elevating pro-inflammatory cytokines. Therefore, understanding endometrial cellular components and signaling mechanisms across pathogenesis are essential for nanotherapeutic exploration against bovine endometritis. The nanotherapeutic discovery that could inhibit infectious signals at the various cell receptors and signal transduction levels, interfering with transcription factors activation and pro-inflammatory cytokines and gene expression, significantly halts endometritis.

Abstract

In order to control and prevent bovine endometritis, there is a need to understand the molecular pathogenesis of the infectious disease. Bovine endometrium is usually invaded by a massive mobilization of microorganisms, especially bacteria, during postpartum dairy cows. Several reports have implicated the Gram-negative bacteria in the pathogenesis of bovine endometritis, with information dearth on the potentials of Gram-positive bacteria and their endotoxins. The invasive bacteria and their ligands pass through cellular receptors such as TLRs, NLRs, and biomolecular proteins of cells activate the specific receptors, which spontaneously stimulates cellular signaling pathways like MAPK, NF-kB and sequentially triggers upregulation of pro-inflammatory cytokines. The cascade of inflammatory induction involves a dual signaling pathway; the transcription factor NF-κB is released from its inhibitory molecule and can bind to various inflammatory genes promoter. The MAPK pathways are concomitantly activated, leading to specific phosphorylation of the NF-κB. The provision of detailed information on the molecular pathomechanism of bovine endometritis with the interaction between host endometrial cells and invasive bacteria in this review would widen the gap of exploring the potential of receptors and signal transduction pathways in nanotechnology-based drug delivery system. The nanotherapeutic discovery of endometrial cell receptors, signal transduction pathway, and cell biomolecules inhibitors could be developed for strategic inhibition of infectious signals at the various cell receptors and signal transduction levels, interfering on transcription factors activation and pro-inflammatory cytokines and genes expression, which may significantly protect endometrium against postpartum microbial invasion.

Signaling pathways in human osteoclasts differentiation: ERK1/2 as a key player

Little is known about the signaling pathways involved in the differentiation of human osteoclasts. The present study evaluated the roles of the Ras/PI3K/Akt/mTOR, Ras/Raf/MEK1/2/ERK1/2, calcium-PKC, and p38 signaling pathways in human osteoclast differentiation. Mononuclear cells were isolated from the peripheral blood of control persons and patients with neurofibromatosis 1 (NF1), and the cells were differentiated into osteoclasts in the presence of signaling pathway inhibitors. Osteoclast differentiation was assessed using tartrate-resistant acid phosphatase 5B. Inhibition of most signaling pathways with chemical inhibitors decreased the number of human osteoclasts and disrupted F-actin ring formation, while the inhibition of p38 resulted in an increased number of osteoclasts, which is a finding contradictory to previous murine studies. However, the p38 inhibition did not increase the bone resorption capacity of the cells. Ras-inhibitor FTS increased osteoclastogenesis in samples from control persons, but an inhibitory effect was observed in NF1 samples. Inhibition of MEK, PI3K, and mTOR reduced markedly the number of NF1-deficient osteoclasts, but no effect was observed in control samples. Western blot analyses showed that the changes in the phosphorylation of ERK1/2 correlated with the number of osteoclasts. Our results highlight the fact that osteoclastogenesis is regulated by multiple interacting signaling pathways and emphasize that murine and human findings related to osteoclastogenesis are not necessarily equivalent.

Fas activation alters tight junction proteins in acute lung injury

Background:The acute respiratory distress syndrome (ARDS) is characterized by protein-rich oedema in the alveolar spaces, a feature in which Fas-mediated apoptosis of the alveolar epithelium has been involved. Objective:To determine whether Fas activation increases protein permeability by mechanisms involving disruption of the paracellular tight junction (TJ) proteins in the pulmonary alveoli. Methods: Protein permeability and the expression of TJ proteins were assessed in vivo in wild-type and Fas-deficient lpr mice 16 hours after the intratracheal instillation of recombinant human soluble Fas ligand (rh-sFasL), and at different time points in vitro in human pulmonary alveolar epithelial cells (HPAEpiC) exposed to rh-sFasL Results:Activation of the Fas pathway increased protein permeability in mouse lungs and altered the expression of the TJ proteins occludin and zonula occludens-1 in the alveolar-capillary membrane in vivo and in human alveolar epithelial cell monolayers in vitro. Blockade of caspase-3, but not inhibition of tyrosine kinase dependent pathways, prevented the alterations in TJ protein expression and permeability induced by the Fas/FasL system in human alveolar cell monolayers in vitro. We also observed that both the Fas-induced increase of protein permeability and disruption of TJ proteins occurred before cell death could be detected in the cell monolayers in vitro. Conclusion:Targeting caspase pathways could prevent the disruption of TJs and reduce the formation of lung oedema in the early stages of ARDS.

Anisomycin, a JNK and p38 activator, suppresses cell-cell junction formation in 2D cultures of K38 mouse keratinocyte cells and reduces claudin-7 expression, with an increase of paracellular permeability in 3D cultures

Keratinocytes in the oral mucosal epithelium, which is a non-keratinized stratified epithelium, are exposed to various stimuli from the oral cavity. JNK and p38 are stress-activated mitogen-activated protein kinases (MAPKs) that are phosphorylated by various stimuli and are involved in the assembly and disassembly of tight junctions (TJs) in keratinocytes. Therefore, we investigated the effects of stress-activated MAPKs on TJs in a mouse keratinocyte cell line during cell-cell junction formation in two-dimensional (2D) cultures or stratification to form non-keratinized epithelium in 3D cultures. In 2D cultures, calcium induced zipper-like staining for ZO-1 at 2 h and string-like staining for ZO-1 at 12 h, which indicated immature and mature cell-cell junctions, respectively. Anisomycin (AM), a JNK and p38 activator, inhibited formation of string-like staining for ZO-1, whereas inhibition of JNK, but not p38, after AM treatment restored string-like staining for ZO-1, although claudins (CLDNs) 4, 6, and 7 did not completely colocalize to ZO-1-positive sites. In 3D cultures, AM treatment for 2 weeks activated only p38, suppressed flattening of the superficial cells, removed CLDN7 from ZO-1-positive spots on the surface of 3D cultures, which represent TJs, and decreased transepithelial electrical resistance. Thus, short-term AM treatment inhibited maturation of cell-cell junctions by JNK, but not p38, activation. p38 activation by long-term AM treatment affected morphology of stratified structures and paracellular permeability, which was increased by CLDN7 removal from TJs. Various chronic stimuli that activate stress-activated MAPKs may weaken the keratinocyte barrier and be involved in TJ-related diseases.

Bridging the gap: Super-resolution microscopy of epithelial cell junctions

Cell junctions are critical for cell adhesion and communication in epithelial tissues. It is evident that the cellular distribution, size, and architecture of cell junctions play a vital role in regulating function. These details of junction architecture have been challenging to elucidate in part due to the complexity and size of cell junctions. A major challenge in understanding these features is attaining high resolution spatial information with molecular specificity. Fluorescence microscopy allows localization of specific proteins to junctions, but with a resolution on the same scale as junction size, rendering internal protein organization unobtainable. Super-resolution microscopy provides a bridge between fluorescence microscopy and nanoscale approaches, utilizing fluorescent tags to reveal protein organization below the resolution limit. Here we provide a brief introduction to super-resolution microscopy and discuss novel findings into the organization, structure and function of epithelial cell junctions.

Scaffolding proteins in the development and maintenance of the epidermal permeability barrier

The skin of mammals and other terrestrial vertebrates protects the organism against the external environment, preventing heat, water and electrolyte loss, as well as entry of chemicals and pathogens. Impairments in the epidermal permeability barrier function are associated with the genesis and/or progression of a variety of pathological conditions, including genetic inflammatory diseases, microbial and viral infections, and photodamage induced by UV radiation. In mammals, the outside-in epidermal permeability barrier is provided by the joint action of the outermost cornified layer, together with assembled tight junctions in granular keratinocytes found in the layers underneath. Tight junctions serve as both outside-in and inside-out barriers, and impede paracellular movements of ions, water, macromolecules and microorganisms. At the molecular level, tight junctions consist of integral membrane proteins that form an extracellular seal between adjacent cells, and associate with cytoplasmic scaffold proteins that serve as links with the actin cytoskeleton. In this review, we address the roles that scaffold proteins play specifically in the establishment and maintenance of the epidermal permeability barrier, and how various pathologies alter or impair their functions.

Expression of claudin-11 by tumor cells in cutaneous squamous cell carcinoma is dependent on the activity of p38δ

The incidence of cutaneous squamous cell carcinoma (cSCC) is rapidly increasing, and the prognosis of patients with metastatic disease is poor. There is an emerging need to identify molecular markers for predicting aggressive behaviour of cSCC. Here, we have examined the role of tight junction (TJ) components in the progression of cSCC. The expression pattern of mRNAs for TJ components was determined with RNA sequencing and oligonucleotide array-based expression analysis from cSCC cell lines (n=8) and normal human epidermal keratinocytes (NHEK, n=5). The expression of CLDN11 was specifically elevated in primary cSCC cell lines (n=5), but low or absent in metastatic cSCC cell lines (n=3) and NHEKs. Claudin-11 was detected in cell-cell contacts of primary cSCC cells in culture by indirect immunofluorescence analysis. Analysis of a large panel of tissue samples from sporadic UV-induced cSCC (n=65), cSCC in situ (n=56), actinic keratoses (n=31), seborrhoeic keratoses (n=7) and normal skin (n=16) by immunohistochemistry showed specific staining for claudin-11 in intercellular junctions of keratinizing tumor cells in well and moderately differentiated cSCCs, whereas no staining for claudin-11 was detected in poorly differentiated tumors. The expression of claudin-11 in cSCC cells was dependent on the activity of p38δ MAPK and knock-down of claudin-11 enhanced cSCC cell invasion. These findings provide evidence for the role of claudin-11 in regulation of cSCC invasion and suggest loss of claudin-11 expression in tumor cells as a biomarker for advanced stage of cSCC.

Diversity of actin architecture in human osteoclasts: network of curved and branched actin supporting cell shape and intercellular micrometer-level tubes

Osteoclasts are multinucleated bone-resorbing cells with a dynamic actin cytoskeleton. Osteoclasts are derived from circulating mononuclear precursors. Confocal and stimulated emission depletion (STED) super-resolution microscopy was used to investigate peripheral blood-derived human osteoclasts cultured on glass surfaces. STED and confocal microscopy demonstrated that the actin was curved and branched, for instance, in the vicinity of membrane ruffles. The overall architecture of the curved actin network extended from the podosomes to the top of the cell. The other novel finding was that a micrometer-level tube containing actin bridged the osteoclasts well above the level of the culture glass. The actin filaments of the tubes originated from the network of curved actin often surrounding a group of nuclei. Furthermore, nuclei were occasionally located inside the tubes. Our findings demonstrated the accumulation of c-Src, cortactin, cofilin, and actin around nuclei suggesting their role in nuclear processes such as the locomotion of nuclei. ARP2/3 labeling was abundant at the substratum level of osteoclasts and in the branched actin network, where it localized to the branching points. We speculate that the actin-containing tubes of osteoclasts may provide a means of transportation of nuclei, e.g., during the fusion of osteoclasts. These novel findings can pave the way for future studies aiming at the elucidation of the differentiation of multinucleated osteoclasts.

Aberrant expression of the tight junction molecules claudin-1 and zonula occludens-1 mediates cell growth and invasion in oral squamous cell carcinoma

We reported that altered cell contact mediated by E-cadherin is an initial event in the pathogenesis of oral epithelial malignancies. To assess other effects of cell adhesion, we examined the expression levels of tight junction (TJ) molecules in oral carcinoma in situ (CIS) and squamous cell carcinoma (SCC). To identify changes in the expression of TJ molecules, we conducted an analysis of the immunohistochemical profiles of claudin-1 (CLDN-1) and zonula occludens-1 (ZO-1) in surgical specimens acquired from patients with oral SCC containing foci of epithelial dysplasia or from patients with CIS. We used immunofluorescence, Western blotting, reverse-transcription polymerase chain reaction, and RNA interference to evaluate the functions of CLDN-1 and ZO-1 in cultured oral SCC cells. TJ molecules were not detected in normal oral epithelial tissues but were expressed in SCC/CIS cells. ZO-1 was localized within the nucleus of proliferating cells. When CLDN-1 expression was inhibited by transfecting cells with specific small interference RNAs, SCC cells dissociated, and their ability to proliferate and invade Matrigel was inhibited. In contrast, although RNA interference-mediated inhibition of ZO-1 expression did not affect cell morphology, it inhibited cell proliferation and invasiveness. Our findings indicated that the detection of TJ molecules in the oral epithelia may serve as a marker for the malignant phenotype of cells in which CLDN-1 regulates proliferation and invasion.

Immunosuppressant MPA Modulates Tight Junction through Epigenetic Activation of MLCK/MLC-2 Pathway via p38MAPK

BACKGROUND

Mycophenolic acid (MPA) is an important immunosuppressive drug (ISD) prescribed to prevent graft rejection in the organ transplanted patients, however, its use is also associated with adverse side effects like sporadic gastrointestinal (GI) disturbances. Recently, we reported the MPA induced tight junctions (TJs) deregulation which involves MLCK/MLC-2 pathway. Here, we investigated the global histone acetylation as well as gene-specific chromatin signature of several genes associated with TJs regulation in Caco-2 cells after MPA treatment.

RESULTS

The epigenetic analysis shows that MPA treatment increases the global histone acetylation levels as well as the enrichment for transcriptional active histone modification mark (H3K4me3) at promoter regions of p38MAPK, ATF-2, MLCK, and MLC-2. In contrast, the promoter region of occludin was enriched for transcriptional repressive histone modification mark (H3K27me3) after MPA treatment. In line with the chromatin status, MPA treatment increased the expression of p38MAPK, ATF-2, MLCK, and MLC-2 both at transcriptional and translational level, while occludin expression was negatively influenced. Interestingly, the MPA induced gene expression changes and functional properties of Caco-2 cells could be blocked by the inhibition of p38MAPK using a chemical inhibitor (SB203580).

CONCLUSIONS

Collectively, our results highlight that MPA disrupts the structure of TJs via p38MAPK-dependent activation of MLCK/MLC-2 pathway that results in decreased integrity of Caco-2 monolayer. These results led us to suggest that p38MAPK-mediated lose integrity of epithelial monolayer could be the possible cause of GI disturbance (barrier dysfunction) in the intestine, leading to leaky style diarrhea observed in the organ-transplanted patients treated with MPA.

Temporal Identification of Dysregulated Genes and Pathways in Clear Cell Renal Cell Carcinoma Based on Systematic Tracking of Disrupted Modules

Objective. The objective of this work is to identify dysregulated genes and pathways of ccRCC temporally according to systematic tracking of the dysregulated modules of reweighted Protein-Protein Interaction (PPI) networks. Methods. Firstly, normal and ccRCC PPI network were inferred and reweighted based on Pearson correlation coefficient (PCC). Then, we identified altered modules using maximum weight bipartite matching and ranked them in nonincreasing order. Finally, gene compositions of altered modules were analyzed, and pathways enrichment analyses of genes in altered modules were carried out based on Expression Analysis Systematic Explored (EASE) test. Results. We obtained 136, 576, 693, and 531 disrupted modules of ccRCC stages I, II, III, and IV, respectively. Gene composition analyses of altered modules revealed that there were 56 common genes (such as MAPK1, CCNA2, and GSTM3) existing in the four stages. Besides pathway enrichment analysis identified 5 common pathways (glutathione metabolism, cell cycle, alanine, aspartate, and glutamate metabolism, arginine and proline metabolism, and metabolism of xenobiotics by cytochrome P450) across stages I, II, III, and IV. Conclusions. We successfully identified dysregulated genes and pathways of ccRCC in different stages, and these might be potential biological markers and processes for treatment and etiology mechanism in ccRCC.

Transcriptional regulators of claudins in epithelial tight junctions

Human gastrointestinal tract is covered by a monolayer of specialized epithelial cells that constitute a protective barrier surface to external toxic and infectious agents along with metabolic and digestive functions. Intercellular junctions, among epithelial cells, such as desmosomes, adherens, gap, and tight junctions (TJs), not only provide mechanical integrity but also limit movement of molecules across the monolayer. TJ is a complex structure composed of approximately 35 different proteins that interact with each other at the apical side of two adjacent epithelial cells. Claudin family proteins are important members of TJ with so far 24 known isoforms in different species. Claudins are structural proteins of TJ that help to control the paracellular movement by forming fence and barrier across the epithelial monolayer. Altered function of claudins is implicated in different form of cancers, inflammatory bowel diseases (IBDs), and leaky diarrhea. Based on their significant role in the molecular architecture of TJ, diversity, and disease association, further understanding about claudin family proteins and their genetic/epigenetic regulators is indispensable.

p38 Mitogen-activated protein kinase and c-Jun NH2-terminal protein kinase regulate the accumulation of a tight junction protein, ZO-1, in cell-cell contacts in HaCaT cells

To investigate the involvement of stress-activated protein kinases, JNK and p38 MAPK, in the assembly of tight junctions in keratinocytes, we treated HaCaT cells with various combinations of SP600125 (an inhibitor of JNK), SB202190 (an inhibitor of p38 MAPK) and anisomycin (an activator of both JNK and p38 MAPK) and examined the localization of ZO-1, an undercoat constitutive protein of the tight junction. Short-term (8h) incubation with SP600125, SB202190 or anisomycin induced the accumulation of ZO-1 in the cell-cell contacts, with reduced ZO-1 staining in the cytoplasm, while only long-term (24h) incubation with SP600125 induced the accumulation of ZO-1. SP600125, SB202190 or SP600125 plus SB202190 treatment induced thin linear staining for ZO-1 in the cell-cell contacts. Anisomycin treatment induced thick and irregular linear staining for ZO-1, while anisomycin plus SP600125 treatment induced zipper-like staining for ZO-1. Anisomycin plus SB202190 treatment or anisomycin plus both SP600125 and SB202190 treatment for 8h failed to lead to the accumulation of ZO-1 in cell-cell contacts, but induced thin linear staining with several gaps 16 h after removal of these agents. These results suggest that the localization of ZO-1 in cell-cell contacts is differently regulated by activation and inhibition of JNK and/or p38 MAPK depending on the incubation period.

p38δ MAPK: Emerging Roles of a Neglected Isoform

p38δ mitogen activated protein kinase (MAPK) is a unique stress responsive protein kinase. While the p38 MAPK family as a whole has been implicated in a wide variety of biological processes, a specific role for p38δ MAPK in cellular signalling and its contribution to both physiological and pathological conditions are presently lacking. Recent emerging evidence, however, provides some insights into specific p38δ MAPK signalling. Importantly, these studies have helped to highlight functional similarities as well as differences between p38δ MAPK and the other members of the p38 MAPK family of kinases. In this review we discuss the current understanding of the molecular mechanisms underlying p38δ MAPK activity. We outline a role for p38δ MAPK in important cellular processes such as differentiation and apoptosis as well as pathological conditions such as neurodegenerative disorders, diabetes, and inflammatory disease. Interestingly, disparate roles for p38δ MAPK in tumour development have also recently been reported. Thus, we consider evidence which characterises p38δ MAPK as both a tumour promoter and a tumour suppressor. In summary, while our knowledge of p38δ MAPK has progressed somewhat since its identification in 1997, our understanding of this particular isoform in many cellular processes still strikingly lags behind that of its counterparts.