Epigenetic Regulation of KPC1 Ubiquitin Ligase Affects the NF-κB Pathway in Melanoma

Abstract

<b>Purpose:</b> Abnormal activation of the NF-κB pathway induces a more aggressive phenotype of cutaneous melanoma. Understanding the mechanisms involved in melanoma NF-κB activation may identify novel targets for this pathway. KPC1, an E3 ubiquitin ligase, is a regulator of the NF-κB pathway. The objective of this study was to investigate the mechanisms regulating KPC1 expression and its clinical impact in melanoma.<b>Experimental Design:</b> The clinical impact of KPC1 expression and its epigenetic regulation were assessed in large cohorts of clinically well-annotated melanoma tissues (tissue microarrays; <i>n</i> = 137, JWCI cohort; <i>n</i> = 40) and The Cancer Genome Atlas database (TCGA cohort, <i>n</i> = 370). Using melanoma cell lines, we investigated the functional interactions between KPC1 and NF-κB, and the epigenetic regulations of KPC1, including DNA methylation and miRNA expression.<b>Results:</b> We verified that KPC1 suppresses melanoma proliferation by processing NF-κB1 p105 into p50, thereby modulating NF-κB target gene expression. Concordantly, KPC1 expression was downregulated in American Joint Committee on Cancer stage IV melanoma compared with early stages (stage I/II <i>P</i> = 0.013, stage III <i>P</i> = 0.004), and low KPC1 expression was significantly associated with poor overall survival in stage IV melanoma (<i>n</i> = 137; HR 1.810; <i>P</i> = 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 <i>r</i> -0.455; <i>P</i> < 0.001), is significantly associated with KPC1 downregulation (JWCI; <i>P</i> = 0.028, TCGA; <i>P</i> = 0.003).<b>Conclusions:</b> This study revealed novel epigenetic regulation of KPC1 associated with NF-κB pathway activation, promoting metastatic melanoma progression. These findings suggest the potential utility of KPC1 and its epigenetic regulation as theranostic targets. <i>Clin Cancer Res; 23(16); 4831-42. ©2017 AACR</i>.