Plakophilin 3 phosphorylation by ribosomal S6 kinases supports desmosome assembly

Plakophilin 4 controls the spatio-temporal activity of RhoA at adherens junctions to promote cortical actin ring formation and tissue tension

Plakophilin 4 (PKP4) is a component of cell-cell junctions that regulates intercellular adhesion and Rho-signaling during cytokinesis with an unknown function during epidermal differentiation. Here we show that keratinocytes lacking PKP4 fail to develop a cortical actin ring, preventing adherens junction maturation and generation of tissue tension. Instead, PKP4-depleted cells display increased stress fibers. PKP4-dependent RhoA localization at AJs was required to activate a RhoA-ROCK2-MLCK-MLC2 axis and organize actin into a cortical ring. AJ-associated PKP4 provided a scaffold for the Rho activator ARHGEF2 and the RhoA effectors MLCK and MLC2, facilitating the spatio-temporal activation of RhoA signaling at cell junctions to allow cortical ring formation and actomyosin contraction. In contrast, association of PKP4 with the Rho suppressor ARHGAP23 reduced ARHGAP23 binding to RhoA which prevented RhoA activation in the cytoplasm and stress fiber formation. These data identify PKP4 as an AJ component that transduces mechanical signals into cytoskeletal organization.

Desmosomes at a glance

Desmosomes are relatives of ancient cadherin-based junctions, which emerged late in evolution to ensure the structural integrity of vertebrate tissues by coupling the intermediate filament cytoskeleton to cell-cell junctions. Their ability to dynamically counter the contractile forces generated by actin-associated adherens junctions is particularly important in tissues under high mechanical stress, such as the skin and heart. Much more than the simple cellular 'spot welds' depicted in textbooks, desmosomes are in fact dynamic structures that can sense and respond to changes in their mechanical environment and external stressors like ultraviolet light and pathogens. These environmental signals are transmitted intracellularly via desmosome-dependent mechanochemical pathways that drive the physiological processes of morphogenesis and differentiation. This Cell Science at a Glance article and the accompanying poster review desmosome structure and assembly, highlight recent insights into how desmosomes integrate chemical and mechanical signaling in the epidermis, and discuss desmosomes as targets in human disease.

Experimentally validated oxidative stress -associated prognostic signatures describe the immune landscape and predict the drug response and prognosis of SKCM

Background

Skin Cutaneous Melanoma (SKCM) incidence is continually increasing, with chemotherapy and immunotherapy being among the most common cancer treatment modalities. This study aims to identify novel biomarkers for chemotherapy and immunotherapy response in SKCM and explore their association with oxidative stress.

Methods

Utilizing TCGA-SKCM RNA-seq data, we employed Weighted Gene Co-expression Network Analysis (WGCNA) and Protein-Protein Interaction (PPI) networks to identify six core genes. Gene co-expression analysis and immune-related analysis were conducted, and specific markers associated with oxidative stress were identified using Gene Set Variation Analysis (GSVA). Single-cell analysis revealed the expression patterns of Oxidative Stress-Associated Genes (OSAG) in the tumor microenvironment. TIDE analysis was employed to explore the association between immune therapy response and OSAG, while CIBERSORT was used to analyze the tumor immune microenvironment. The BEST database demonstrated the impact of the Oxidative Stress signaling pathway on chemotherapy drug resistance. Immunohistochemical staining and ROC curve evaluation were performed to assess the protein expression levels of core genes in SKCM and normal samples, with survival analysis utilized to determine their diagnostic value.

Results

We identified six central genes associated with SKCM metastasis, among which the expression of DSC2 and DSC3 involved in the oxidative stress pathway was closely related to immune cell infiltration. DSC2 influenced drug resistance in SKMC patients. Furthermore, downregulation of DSC2 and DSC3 expression enhanced the response of SKCM patients to immunotherapy.

Conclusion

This study identified two Oxidative Stress-Associated genes as novel biomarkers for SKCM. Additionally, targeting the oxidative stress pathway may serve as a new strategy in clinical practice to enhance SKCM chemotherapy and sensitivity.

Role and function of plakophilin 3 in cancer progression and skin disease

Plakophilin 3 (PKP3), a component of desmosome, is aberrantly expressed in many kinds of human diseases, especially in cancers. Through direct interaction, PKP3 binds with a series of desmosomal proteins, such as desmoglein, desmocollin, plakoglobin, and desmoplakin, to initiate desmosome aggregation, then promotes its stability. As PKP3 is mostly expressed in the skin, loss of PKP3 promotes the development of several skin diseases, such as paraneoplastic pemphigus, pemphigus vulgaris, and hypertrophic scar. Moreover, accumulated clinical data indicate that PKP3 dysregulates in diverse cancers, including breast, ovarian, colon, and lung cancers. Numerous lines of evidence have shown that PKP3 plays important roles in multiple cellular processes during cancer progression, including metastasis, invasion, tumor formation, autophagy, and proliferation. This review examines the diverse functions of PKP3 in regulating tumor formation and development in various types of cancers and summarizes its detailed mechanisms in the occurrence of skin diseases.

Photobiomodulation Facilitates Rat Cutaneous Wound Healing by Promoting Epidermal Stem Cells and Hair Follicle Stem Cells Proliferation

BACKGROUND

Cutaneous wound healing represents a common fundamental phenomenon requiring the participation of cells of distinct types and a major concern for the public. Evidence has confirmed that photobiomodulation (PBM) using near-infrared (NIR) can promote wound healing, but the  cells involved and the precise molecular mechanisms remain elusive.

METHODS

Full-thickness skin defects with a diameter of 1.0 cm were made on the back of rats and randomly divided into the control group, 10 J, 15 J, and 30 J groups. The wound healing rate at days 4, 8, and 12 postoperatively was measured. HE and Masson staining was conducted to reveal the histological characteristics. Immunofluorescence staining was performed to label the epidermal stem cells (ESCs) and hair follicle stem cells (HFSCs). Western blot was performed to detect the expressions of proteins associated with ESCs and HFSCs. Cutaneous wound tissues were collected for RNA sequencing. Gene ontology and the Kyoto Encyclopedia of Genes and Genomes analysis was performed, and the hub genes were identified using CytoHubba and validated by qRT-PCR.

RESULTS

PBM can promote reepithelialization, extracellular matrix deposition, and wound healing, increase the number of KRT14+/PCNA+ ESCs and KRT15+/PCNA+ HFSCs, and upregulate the protein expression of P63, Krt14, and PCNA. Three hundred and sixty-six differentially expressed genes (DEGs) and 7 hub genes including Sox9, Krt5, Epcam, Cdh1, Cdh3, Dsp, and Pkp3 were identified. These DEGs are enriched in skin development, cell junction, and cadherin binding involved in cell-cell adhesion etc., while these hub genes are related to skin derived stem cells and cell adhesion.

CONCLUSION

PBM accelerates wound healing by enhancing reepithelialization through promoting ESCs and HFSCs proliferation and elevating the expression of genes associated with stem cells and cell adhesion. This may provide a valuable alternative strategy to promote wound healing and reepithelialization by modulating the proliferation of skin derived stem cells and regulating genes related to cell adhesion.

Plakophilin 3 facilitates G1/S phase transition and enhances proliferation by capturing RB protein in the cytoplasm and promoting EGFR signaling

Plakophilin 3 (PKP3) is a component of desmosomes and is frequently overexpressed in cancer. Using keratinocytes either lacking or overexpressing PKP3, we identify a signaling axis from ERK to the retinoblastoma (RB) protein and the E2F1 transcription factor that is controlled by PKP3. RB and E2F1 are key components controlling G1/S transition in the cell cycle. We show that PKP3 stimulates the activity of ERK and its target RSK1. This inhibits expression of the transcription factor RUNX3, a positive regulator of the CDK inhibitor CDKN1A/p21, which is also downregulated by PKP3. Elevated CDKN1A prevents RB phosphorylation and E2F1 target gene expression, leading to delayed S phase entry and reduced proliferation in PKP3-depleted cells. Elevated PKP3 expression not only increases ERK activity but also captures phosphorylated RB (phospho-RB) in the cytoplasm to promote E2F1 activity and cell-cycle progression. These data identify a mechanism by which PKP3 promotes proliferation and acts as an oncogene.

The Desmosome-Keratin Scaffold Integrates ErbB Family and Mechanical Signaling to Polarize Epidermal Structure and Function

While classic cadherin-actin connections in adherens junctions (AJs) have ancient origins, intermediate filament (IF) linkages with desmosomal cadherins arose in vertebrate organisms. In this mini-review, we discuss how overlaying the IF-desmosome network onto the existing cadherin-actin network provided new opportunities to coordinate tissue mechanics with the positioning and function of chemical signaling mediators in the ErbB family of receptor tyrosine kinases. We focus in particular on the complex multi-layered outer covering of the skin, the epidermis, which serves essential barrier and stress sensing/responding functions in terrestrial vertebrates. We will review emerging data showing that desmosome-IF connections, AJ-actin interactions, ErbB family members, and membrane tension are all polarized across the multiple layers of the regenerating epidermis. Importantly, their integration generates differentiation-specific roles in each layer of the epidermis that dictate the form and function of the tissue. In the basal layer, the onset of the differentiation-specific desmosomal cadherin desmoglein 1 (Dsg1) dials down EGFR signaling while working with classic cadherins to remodel cortical actin cytoskeleton and decrease membrane tension to promote cell delamination. In the upper layers, Dsg1 and E-cadherin cooperate to maintain high tension and tune EGFR and ErbB2 activity to create the essential tight junction barrier. Our final outlook discusses the emerging appreciation that the desmosome-IF scaffold not only creates the architecture required for skin's physical barrier but also creates an immune barrier that keeps inflammation in check.

Desmosomes as Signaling Hubs in the Regulation of Cell Behavior

Desmosomes are intercellular junctions, which preserve tissue integrity during homeostatic and stress conditions. These functions rely on their unique structural properties, which enable them to respond to context-dependent signals and transmit them to change cell behavior. Desmosome composition and size vary depending on tissue specific expression and differentiation state. Their constituent proteins are highly regulated by posttranslational modifications that control their function in the desmosome itself and in addition regulate a multitude of desmosome-independent functions. This review will summarize our current knowledge how signaling pathways that control epithelial shape, polarity and function regulate desmosomes and how desmosomal proteins transduce these signals to modulate cell behavior.

Identification of lymphocyte cell-specific protein-tyrosine kinase (LCK) as a driver for invasion and migration of oral cancer by tumor heterogeneity exploitation

BACKGROUND

Cancer metastases are the main cause of lethality. The five-year survival rate for patients diagnosed with advanced stage oral cancer is 30%. Hence, the identification of novel therapeutic targets is an urgent need. However, tumors are comprised of a heterogeneous collection of cells with distinct genetic and molecular profiles that can differentially promote metastasis making therapy development a challenging task. Here, we leveraged intratumoral heterogeneity in order to identify drivers of cancer cell motility that might be druggable targets for anti-metastasis therapy.

METHODS

We used 2D migration and 3D matrigel-based invasion assays to characterize the invasive heterogeneity among and within four human oral cancer cell lines in vitro. Subsequently, we applied mRNA-sequencing to map the transcriptomes of poorly and strongly invasive subclones as well as primary tumors and matched metastasis.

RESULTS

We identified SAS cells as a highly invasive oral cancer cell line. Clonal analysis of SAS yielded a panel of 20 subclones with different invasive capacities. Integrative gene expression analysis identified the Lymphocyte cell-specific protein-tyrosine kinase (LCK) as a druggable target gene associated with cancer cell invasion and metastasis. Inhibition of LCK using A-770041 or dasatinib blocked invasion of highly aggressive SAS cells. Interestingly, reduction of LCK activity increased the formation of adherens junctions and induced cell differentiation.

CONCLUSION

Analysis of invasive heterogeneity led to the discovery of LCK as an important regulator of motility in oral cancer cells. Hence, small molecule mediated inhibition of LCK could be a promising anti-metastasis therapy option for oral cancer patients.