Epigenetic regulation of KPC1 ubiquitin ligase affects the NF-κB pathway in melanoma

Purpose: Abnormal activation of the NF-kB pathway induces a more aggressive phenotype of cutaneous melanoma. Understanding the mechanisms involved in melanoma NF-kB activation may identify novel targets for this pathway. KPC1, an E3 ubiquitin ligase, is a regulator of the NF-kB pathway. The objective of this study was to investigate the mechanisms regulating KPC1 expression and its clinical impact in melanoma. Experimental Design: The clinical impact of KPC1 expression and its epigenetic regulation were assessed in large cohorts of clinically well-annotated melanoma tissues (tissue microarrays; n ¼ 137, JWCI cohort; n ¼ 40) and The Cancer Genome Atlas database (TCGA cohort, n ¼ 370). Using melanoma cell lines, we investigated the functional interactions between KPC1 and NF-kB, and the epigenetic regulations of KPC1, including DNA methylation and miRNA expression. Results: We verified that KPC1 suppresses melanoma proliferation by processing NF-kB1 p105 into p50, thereby modulating NF-kB target gene expression. Concordantly, KPC1 expression was downregulated in American Joint Committee on Cancer stage IV melanoma compared with early stages (stage I/II P ¼ 0.013, stage III P ¼ 0.004), and low KPC1 expression was significantly associated with poor overall survival in stage IV melanoma (n ¼ 137; HR 1.810; P ¼ 0.006). Furthermore, our data showed that high miR-155-5p expression, which is controlled by DNA methylation at its promoter region (TCGA; Pearson's r 0.455; P < 0.001), is significantly associated with KPC1 downregulation (JWCI; P ¼ 0.028, TCGA; P ¼ 0.003). Conclusions: This study revealed novel epigenetic regulation of KPC1 associated with NF-kB pathway activation, promoting metastatic melanoma progression. These findings suggest the potential utility of KPC1 and its epigenetic regulation as theranostic targets.