Differential expression of p120-catenin 1 and 3 isoforms in epithelial tissues

Delta-catenin is required for cell proliferation in virus positive Merkel cell carcinoma cell lines but not in human fibroblasts

Merkel cell carcinoma (MCC) is a highly aggressive neuroendocrine skin cancer often driven by the integration of Merkel cell polyomavirus (MCPyV) into the host genome and the persistent expression of its viral oncoproteins, small tumor (ST) antigen and truncated large tumor (t-LT) antigen. While human fibroblasts support MCPyV replication, the cell of origin for MCC remains unknown. We hypothesized that MCPyV initially replicates in fibroblasts but, in rare cases, infects Merkel cell progenitors, contributing to MCC development. Using TurboID mass spectrometry, we identified δ-catenin as a novel ST interactor in fibroblasts. However, while ST binds δ-catenin in fibroblasts, this interaction is absent in virus-positive (VP)-MCC cell lines. Despite this, δ-catenin is essential for VP-MCC, but not for fibroblast, cell proliferation. We found that fibroblasts predominantly express δ-catenin isoform 1, whereas VP-MCC cells mainly express isoform 3. Overexpression of isoform 1 in VP-MCC failed to restore ST binding. δ-catenin promotes VP-MCC proliferation by regulating cell cycle gene expression through its interaction with Kaiso, a transcriptional repressor. Additionally, we found that LSD1 (KDM1A) regulates δ-catenin isoform 3 expression by modulating ESRP1, a δ-catenin splicing factor. Our findings reveal novel host factors involved in MCPyV infection and MCC tumorigenesis, suggesting that the host cell supporting viral replication and the MCC cell of origin may be distinct cell types.

Epithelial-mesenchymal transition in age-associated thymic involution: Mechanisms and therapeutic implications

The thymus is a critical immune organ with endocrine and immune functions that plays important roles in the physiological and pathological processes of the body. However, with aging, the thymus undergoes degenerative changes leading to decreased production and output of naive T cells and the secretion of thymic hormones and related cytokines, thereby promoting the occurrence and development of various age-associated diseases. Therefore, identifying essential processes that regulate age-associated thymic involution is crucial for long-term control of thymic involution and age-associated disease progression. Epithelial-mesenchymal transition (EMT) is a well-established process involved in organ aging and functional impairment through tissue fibrosis in several organs, such as the heart and kidney. In the thymus, EMT promotes fibrosis and potentially adipogenesis, leading to thymic involution. This review focuses on the factors involved in thymic involution, including oxidative stress, inflammation, and hormones, from the perspective of EMT. Furthermore, current interventions for reversing age-associated thymic involution by targeting EMT-associated processes are summarized. Understanding the key mechanisms of thymic involution through EMT as an entry point may promote the development of new therapies and clinical agents to reverse thymic involution and age-associated disease.

Regulation of Epithelial-Mesenchymal Transitions by Alternative Splicing: Potential New Area for Cancer Therapeutics

The epithelial-mesenchymal transition (EMT) is a complicated biological process in which cells with epithelial phenotype are transformed into mesenchymal cells with loss of cell polarity and cell-cell adhesion and gain of the ability to migrate. EMT and the reverse mesenchymal-epithelial transitions (METs) are present during cancer progression and metastasis. Using the dynamic switch between EMT and MET, tumour cells can migrate to neighbouring organs or metastasize in the distance and develop resistance to traditional chemotherapy and targeted drug treatments. Growing evidence shows that reversing or inhibiting EMT may be an advantageous approach for suppressing the migration of tumour cells or distant metastasis. Among different levels of modulation of EMT, alternative splicing (AS) plays an important role. An in-depth understanding of the role of AS and EMT in cancer is not only helpful to better understand the occurrence and regulation of EMT in cancer progression, but also may provide new therapeutic strategies. This review will present and discuss various splice variants and splicing factors that have been shown to play a crucial role in EMT.

Role of the blood-spinal cord barrier: An adheren junction regulation mechanism that promotes chronic postsurgical pain

Chronic postsurgical pain (CPSP) is a serious postoperative complication with high incidence, and its pathogenesis involves neuroimmune interactions and the breakdown of the blood-spinal cord barrier (BSCB), the decreased level of adheren junction (AJ)-related proteins is an important cause of BSCB injury. Vascular endothelial-cadherin (VE-cadherin) and p120 catenin (p120) constitute the endothelial barrier adheren junction. The Src/p120/VE-cadherin pathway is involved in the regulation of the endothelial barrier function. However, the role of the BSCB-AJ regulatory mechanism in CPSP has not been reported. In this study, we established a skin/muscle incision and retraction (SMIR) model and evaluated the paw withdrawal threshold (PWT), the effects of an Src inhibitor and p120 knockdown on p-Src, p120 and VE-cadherin expression, as well as BSCB-AJ function in rat spinal cord were observed to explore the regulation of BSCB-AJ function by the p-Src/p120/VE-cadherin pathway in promoting SMIR-induced CPSP. The levels of p-Src, p120 and VE-cadherin in the spinal cord were detected by Western blot. Meanwhile, BSCB permeability test was used to detect the changes in BCSB function. Finally, the spatial and temporal localization of p120 in spinal cord was detected by immunofluorescence. Our findings indicated that p-Src/p120/VE-cadherin could induce BSCB-AJ dysfunction and promote the development of CPSP.

The global Protein-RNA interaction map of ESRP1 defines a post-transcriptional program that is essential for epithelial cell function

The epithelial splicing regulatory proteins, ESRP1 and ESRP2, are essential for mammalian development through the regulation of a global program of alternative splicing of genes involved in the maintenance of epithelial cell function. To further inform our understanding of the molecular functions of ESRP1, we performed enhanced crosslinking immunoprecipitation coupled with high-throughput sequencing (eCLIP) in epithelial cells of mouse epidermis. The genome-wide binding sites of ESRP1 were integrated with RNA-Seq analysis of alterations in splicing and total gene expression that result from epidermal ablation of Esrp1 and Esrp2. These studies demonstrated that ESRP1 functions in splicing regulation occur primarily through direct binding in a position-dependent manner to promote either exon inclusion or skipping. In addition, we also identified widespread binding of ESRP1 in 3' and 5' untranslated regions (UTRs) of genes involved in epithelial cell function, suggesting that its post-transcriptional functions extend beyond splicing regulation.

p120 regulates E-cadherin expression in nasal epithelial cells in chronic rhinosinusitis

BACKGROUND

The epithelial barrier plays an important role in the regulation of immune homeostasis. The effect of the immune environment on E-cadherin has been demonstrated in previous studies. This discovery prompted new research on the targeting mechanism of E-cadherin in chronic rhinosinusitis (CRS).

METHODS

E-cadherin and p120 expression was determined by quantitative RT-PCR, and western blot. The interaction between E-cadherin and p120 was assessed by immunofluorescence staining and coimmunoprecipitation assays. Human nasal epithelial cells (HNECs) were cultured with submerged methods and transfected with p120-specific small interfering RNA. In other experiments, HNECs differentiated with the air-liquid interface (ALI) method were stimulated with various cytokines and Toll-like receptor (TLR) agonists. The barrier properties of differentiated HNECs were determined by assessing fluorescent dextran permeability.

RESULTS

E-cadherin and p120 expression was decreased in HNECs from patients with CRS, and the p120 protein expression level was positively correlated with that of E-cadherin. Two isoforms of p120 (p120-1 and p120-3) were expressed in HNECs, with p120-3 being the main isoform. Knocking down p120 in HNECs cultured under submerged conditions significantly reduced the E-cadherin protein expression. The Rac1 inhibitor NSC23766 reversed the protein expression of E-cadherin in p120 knockdown experiments. Inflammatory mediators, including IL-4, TNF-α, TGF- β, LPS and IFN-Î, reduced E-cadherin and p120 protein expression and increased paracellular permeability. Dexamethasone abolished the downregulation of E-cadherin and p120 caused by inflammatory mediators.

CONCLUSIONS

p120 is involved in regulating E-cadherin protein expression in CRS. Dexamethasone may alleviate the reduction in E-cadherin and p120 protein expression caused by inflammatory mediators.

A cell-to-patient machine learning transfer approach uncovers novel basal-like breast cancer prognostic markers amongst alternative splice variants

BACKGROUND

Breast cancer is amongst the 10 first causes of death in women worldwide. Around 20% of patients are misdiagnosed leading to early metastasis, resistance to treatment and relapse. Many clinical and gene expression profiles have been successfully used to classify breast tumours into 5 major types with different prognosis and sensitivity to specific treatments. Unfortunately, these profiles have failed to subclassify breast tumours into more subtypes to improve diagnostics and survival rate. Alternative splicing is emerging as a new source of highly specific biomarkers to classify tumours in different grades. Taking advantage of extensive public transcriptomics datasets in breast cancer cell lines (CCLE) and breast cancer tumours (TCGA), we have addressed the capacity of alternative splice variants to subclassify highly aggressive breast cancers.

RESULTS

Transcriptomics analysis of alternative splicing events between luminal, basal A and basal B breast cancer cell lines identified a unique splicing signature for a subtype of tumours, the basal B, whose classification is not in use in the clinic yet. Basal B cell lines, in contrast with luminal and basal A, are highly metastatic and express epithelial-to-mesenchymal (EMT) markers, which are hallmarks of cell invasion and resistance to drugs. By developing a semi-supervised machine learning approach, we transferred the molecular knowledge gained from these cell lines into patients to subclassify basal-like triple negative tumours into basal A- and basal B-like categories. Changes in splicing of 25 alternative exons, intimately related to EMT and cell invasion such as ENAH, CD44 and CTNND1, were sufficient to identify the basal-like patients with the worst prognosis. Moreover, patients expressing this basal B-specific splicing signature also expressed newly identified biomarkers of metastasis-initiating cells, like CD36, supporting a more invasive phenotype for this basal B-like breast cancer subtype.

CONCLUSIONS

Using a novel machine learning approach, we have identified an EMT-related splicing signature capable of subclassifying the most aggressive type of breast cancer, which are basal-like triple negative tumours. This proof-of-concept demonstrates that the biological knowledge acquired from cell lines can be transferred to patients data for further clinical investigation. More studies, particularly in 3D culture and organoids, will increase the accuracy of this transfer of knowledge, which will open new perspectives into the development of novel therapeutic strategies and the further identification of specific biomarkers for drug resistance and cancer relapse.

Collective invasion induced by an autocrine purinergic loop through connexin-43 hemichannels

Progression of epithelial cancers predominantly proceeds by collective invasion of cell groups with coordinated cell-cell junctions and multicellular cytoskeletal activity. Collectively invading breast cancer cells express the gap junction protein connexin-43 (Cx43), yet whether Cx43 regulates collective invasion remains unclear. We here show that Cx43 mediates gap-junctional coupling between collectively invading breast cancer cells and, via hemichannels, adenosine nucleotide/nucleoside release into the extracellular space. Using molecular interference and rescue strategies, we identify that Cx43 hemichannel function, but not intercellular communication, induces leader cell activity and collective migration through the engagement of the adenosine receptor 1 (ADORA1) and AKT signaling. Accordingly, pharmacological inhibition of ADORA1 or AKT signaling caused leader cell collapse and halted collective invasion. ADORA1 inhibition further reduced local invasion of orthotopic mammary tumors in vivo, and joint up-regulation of Cx43 and ADORA1 in breast cancer patients correlated with decreased relapse-free survival. This identifies autocrine purinergic signaling, through Cx43 hemichannels, as a critical pathway in leader cell function and collective invasion.

P120 Catenin Isoforms Differentially Associate with Breast Cancer Invasion and Metastasis

Tumor metastasis is the endpoint of tumor progression and depends on the ability of tumor cells to locally invade tissue, transit through the bloodstream and ultimately to colonize secondary organs at distant sites. P120 catenin (p120) has been implicated as an important regulator of metastatic dissemination because of its roles in cell–cell junctional stability, cytoskeletal dynamics, growth and survival. However, conflicting roles for p120 in different tumor models and steps of metastasis have been reported, and the understanding of p120 functions is confounded by the differential expression of p120 isoforms, which differ in N-terminal length, tissue localization and, likely, function. Here, we used in silico exon expression analyses, in vitro invasion assays and both RT-PCR and immunofluorescence of human tumors. We show that alternative exon usage favors expression of short isoform p120-3 in 1098 breast tumors and correlates with poor prognosis. P120-3 is upregulated at the invasive front of breast cancer cells migrating as collective groups in vitro. Furthermore, we demonstrate in histological sections of 54 human breast cancer patients that p120-3 expression is maintained throughout the metastatic cascade, whereas p120-1 is differentially expressed and diminished during invasion and in metastases. These data suggest specific regulation and functions of p120-3 in breast cancer invasion and metastasis.