Plakophilin 1 (PKP1), a member of the p120ctn subfamily of the armadillo (ARM)-repeat-containing proteins, is an important structural component of cell-cell adhesion scaffolds although it can also be ubiquitously found in the cytoplasm and the nucleus. RYBP (RING 1A and YY1 binding protein) is a multifunctional intrinsically disordered protein (IDP) best described as a transcriptional regulator. Both proteins are involved in the development and metastasis of several types of tumors. We studied the binding of the armadillo domain of PKP1 (ARM-PKP1) with RYBP by using in cellulo methods, namely immunofluorescence (IF) and proximity ligation assay (PLA), and in vitro biophysical techniques, namely fluorescence, far-ultraviolet (far-UV) circular dichroism (CD), and isothermal titration calorimetry (ITC). We also characterized the binding of the two proteins by using in silico experiments. Our results showed that there was binding in tumor and non-tumoral cell lines. Binding in vitro between the two proteins was also monitored and found to occur with a dissociation constant in the low micromolar range (~10 μM). Finally, in silico experiments provided additional information on the possible structure of the binding complex, especially on the binding ARM-PKP1 hot-spot. Our findings suggest that RYBP might be a rescuer of the high expression of PKP1 in tumors, where it could decrease the epithelial-mesenchymal transition in some cancer cells.

The study aimed to investigate the clinical significance of the interaction between hypoxia and the immune system in esophageal squamous cell carcinoma (ESCC) microenvironment. A comprehensive evaluation of 13 hypoxia phenotype-related genes (HPRs) was conducted using data from TCGA-ESCC and two GEO cohorts. Three distinct HPRclusters were identified, and the HPRscore was established as an independent prognostic factor (p = 0.001), with higher scores indicating poorer prognosis. The HPRscore was validated in various immunotherapy cohorts, demonstrating its efficacy in evaluating immunotherapy and chemotherapy outcomes. Additionally, phenome-wide association study (PheWAS) analysis showed that PKP1 had no significant correlation with other traits at the gene level. PKP1 was identified as a potential prognostic marker for ESCC, with upregulated expression observed in ESCC patients. In vitro experiments showed that the knockdown of PKP1 inhibited ESCC cell proliferation and migration. These findings suggest that the novel HPRscore and PKP1 may serve as prognostic tools and therapeutic targets for ESCC patients.

The incidence rate of melanoma varies across regions, with Europe, the United States, and Australia having 10-25, 20-30, and 50-60 cases per 1 00 000 people. In China, patients with melanoma exhibit different clinical manifestations, pathogenesis, and outcomes. Current treatments include surgery, adjuvant therapy, and immune checkpoint inhibitors. Nonetheless, complications may arise during treatment. Melanoma development is heavily reliant on cell adhesion molecules (CAMs), and studying these molecules could provide new research directions for metastasis and progression. CAMs include the integrin, immunoglobulin, selectin, and cadherin families, and they affect multiple processes, such as maintenance, morphogenesis, and migration of adherens junction. In this study, a cell adhesion-related risk prognostic signature was constructed using bioinformatics methods, and survival analysis was performed. Plakophilin 1 (PKP1) was observed to be crucial to the immune microenvironment and has significant effects on melanoma cell proliferation, migration, invasion, and the cell cycle. This signature demonstrates high reliability and has potential for clinical applications.

Immunotherapy is an individualized therapeutic strategy for nasopharyngeal carcinoma (NPC). However, few molecular targets are clinically satisfactory. This work aimed to integrate bulk and single-cell RNA sequencing data to identify novel biomarkers involved in NPC. We performed differentially expressed gene (DEG) analysis, Gene Ontology (GO) enrichment, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis, and immune cell infiltration analysis prior to correlation analysis of the identified genes and immune cells and further assessed the prognostic effects of the biomarkers and immune cells in NPC. As a result, PKP1, a potential molecular biomarker associated with immune infiltration, and tumor-infiltrating lymphocyte-B cells (TIL-Bs) were identified as promising therapeutic targets for NPC. Importantly, immunohistochemistry (IHC) validated that PKP1 protein expression was mainly found in NPC cells rather than noncancerous cells. In addition, the tumor microenvironment (TME) of NPC was characterized by the infiltration of more dendritic cells (DCs) and γδT cells but fewer B cells. Our results suggest that the interaction of PKP1 and TIL-B cells is involved in NPC development. It is possible that TIL-B cells produce immunoglobulin G (IgG) to tumor antigens, such as PKP1, or viral antigens, including EBV and HPV, to execute antitumor ability through DC and T cells. In response, NPC cells express proteins such as PKP1 (absent in normal nasopharynx) to induce myeloid-derived suppressor cell (MDSC) expansion, which subsequently impairs the proliferation of B cells and results in B-cell death by generating iNOS and NOX2. In summary, our findings provide a potential therapeutic strategy for NPC by disrupting the interaction of PKP1 and TIL-Bs in the TME.

OBJECTIVE: To identify the potential differential genes between primary and metastatic melanoma, screen out immune-related genes in core genes and analyze their immune correlation, thus searching for the early diagnostic biomarkers of cutaneous malignant melanoma (CMM) and the targets of curbing metastasis.
METHODS: We analyzed two microarray datasets (GSE8401 and GSE46517) derived from the Gene Expression Omnibus (GEO) database. Differentially expressed genes (DEGs) between primary and metastatic melanoma were screened out using the GEO2R tool. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis were performed to identify the functions and pathways of DEGs. We analyzed protein-protein interaction of these DEGs based on the Search Tool for the Retrieval of Interacting Genes database and showed by Cytoscape software. In addition, the online Gene Expression Profiling Interactive Analysis tool (GEPIA) was used to analyze the prognostic value of hub genes expressed in metastatic melanoma patients. Immune-related genes in hub genes were screened and further analyzed.
RESULTS: A total of 178 upregulated DEGs and 4 downregulated DEGs were identified. 23 terms and 4 pathways were confirmed related to metastatic melanoma. Ten hub genes with a high degree of connectivity were found. Overexpression of three hub genes (DSG1, FLG, PKP1) (P<0.01) was associated with metastasis and poor prognosis of CMM. Among them, the patients with overexpression of PKP1 suffered shorter survival. In addition, 2 immune-related genes (EGFR and CDH1) in hub genes were screened out and both of them were related to anti-tumor immunity, although their expression level did not affect the overall survival of CMM patients significantly.
CONCLUSIONS: Our study suggests that DSG1, FLG and PKP1 were overexpressed in metastatic melanoma compared with primary melanoma, and overexpression of these three genes was an unfavorable prognostic factor ifor CMM patients, which may indicate that they are associated with promoting metastasis of malignant melanoma. EGFR and CDH1 play a crucial role in anti-tumor immunity for CMM. Further research is needed to explore the value of these genes in the inhibition of metastasis and treatment of CMM.

OBJECTIVE: Malignant melanoma is a fatal cancer with high metastatic characteristics. Approximately 80% of skin cancer deaths are caused by metastatic melanoma. It has been established that the metastatic ability of melanoma is regulated by an intricate gene interconnection network. Thus, the aim of this study was to identify and validate hub genes associated with metastatic melanoma and to further illustrate its potential mechanisms.
METHODS: The method of weighted gene coexpression network analysis (WGCNA) was applied to explore potential regulatory targets and investigate the relationship between the key module and hub genes associated with the metastasis ability of melanoma.
RESULTS: In the turquoise module, 26 hub genes were initially selected, and 6 of them were identified as \"real\" hub genes with high connectivity in the protein-protein interaction network. In terms of validation, PKP1 had the highest correlation with metastasis among all the \"real\" hub genes. Data obtained from the GEPIA database and the Gene Expression Omnibus database showed a lower expression of PKP1 in melanoma tissues compared to normal skin tissues. The results also showed that PKP1 was downregulated in metastatic melanomas (n = 367) compared with primary melanomas (n = 103) in The Cancer Genome Atlas (TCGA) database (n = 470). Furthermore, an ROC curve showed that PKP1 expression had good power in the diagnostics of both primary melanoma (p =  5.30e-06, AUC = 0.8) and metastatic melanoma (p =  1.13e-10, AUC = 0.925). We also found that PKP1 could distinguish low- and high-grade of metastatic melanomas and was associated with inflammatory melanoma. Moreover, in a tumor-bearing mouse model, melanoma tissues also showed lower mRNA expression of PKP1 than the adjacent normal skin. Finally, Gene Set Enrichment Analysis indicated that the calcium signaling was significantly enriched in metastatic melanoma with highly expressed PKP1.
CONCLUSIONS: PKP1 was identified as a new potential tumor suppressor in human melanoma, likely through regulating calcium signaling pathways.

Plakophilin (PKP) 1 is frequently downregulated in prostate cancer and therefore may play a tumor-suppressive role. In the present study, we stably knocked down PKP1 in the non-neoplastic, prostatic BPH-1 cell line. In the PKP1-deficient cells, the expression of keratin 14 was lost, and the apoptosis rate was significantly reduced indicating that the cells acquired new biological capabilities. Moreover, we analyzed the gene expression profile of the PKP1-deficient BPH-1 cells. Among the genes that were significantly altered upon PKP1 knockdown, we noticed several extracellular matrix (ECM)-related genes and identified sparc/osteonectin, cwcv, and kazal-like domains proteoglycan 1 (SPOCK1/testican-1) as a gene of interest. SPOCK1 is a component of the ECM and belongs to a matricellular protein family named secreted protein, acidic, cysteine-rich (SPARC). The role of SPOCK1 in prostate cancer has not been clearly elucidated. We analyzed SPOCK1 mRNA expression levels in different cancer databases and characterized its expression in 136 prostatic adenocarcinomas by immunohistochemistry and western blot. SPOCK1 revealed a cytoplasmic localization in the glandular epithelium of the prostate and showed a significant upregulation of mRNA and protein in prostate tumor samples. Our findings support the hypothesis that PKP1 may have a tumor-suppressive function and suggest an important role of SPOCK1 in prostate tumor progression. Collectively, altered expression of PKP1 and SPOCK1 appears to be a frequent and critical event in prostate cancer.