Abstract 3541: Epigenetic regulation of KPC1 ubiquitin ligase has a regulatory role on the NF-κB pathway in metastatic melanoma

Purpose: Abnormal activation of the NF-κB pathway promotes a more aggressive phenotype of cutaneous malignant melanoma. Understanding the mechanisms regulating the NF-κB pathway in melanoma is of critical importance. KPC1 (RNF123) is an E3 ubiquitin ligase that leads to proteasomal processing of precursor NF-κB1 p105 into mature p50, one of the most important steps in the NF-κB pathway regulation. We demonstrated novel epigenetic mechanisms affecting KPC1 expression that lead to an abnormal activation of the NF-κB pathway, which was significant during tumor progression in melanoma patients. Experimental Design: Initially using melanoma cell lines, we investigated the functional interactions between KPC1 and NF-κB, and the epigenetic regulations of KPC1, including microRNA targeted interaction and DNA methylation. The clinical impact of KPC1 expression and these epigenetic regulations were further assessed in large cohorts of clinically well-annotated melanoma tissues (tissue micro-arrays; n=137, JWCI cohort; n=40) and melanoma TCGA database cohort (n=370). High-throughput RNA sequencing, reverse-phase protein array and human methylation 450k platform were utilized for comprehensive analyses. Results: Initially using metastatic melanoma cell lines, we verified that KPC1 promotes processing of NF-κB1 p105 into p50, thereby modulates NF-κB-target gene expression and suppresses melanoma cell proliferation. Concordantly in melanoma tissue, KPC1 expression was down-regulated in AJCC stage IV melanoma compared to early stages (JWCI cohort stage I/II p=0.013, stage III p=0.004), whereby low KPC1 expression was significantly associated with poor overall survival in stage IV melanoma (tissue micro-arrays, n=137, Hazard Ratio 1.810, p=0.006). Furthermore, epigenetic mechanisms regulating KPC1, particularly miR-155-5p and DNA methylation level at its promoter region, was shown to be significant in melanoma lines. This regulatory mechanism was validated in clinical melanoma tissues. High miR-155-5p expression, which is negatively regulated by its promoter DNA methylation level (melanoma TCGA database cohort; Pearson's r -0.455, p Conclusions: We identified miR-155-5p, which is epigenetically controlled by its promoter methylation, has a regulatory role on KPC1 expression. These interactions promote to down-regulation of KPC1 and abnormal NF-κB pathway activation, leading to highly proliferative melanoma cells and poor clinical outcomes. These findings suggest utility of KPC1 expression level for stratification of stage IV melanoma patients, and the importance of the miR-155-5p-KPC1-NF-κB-axis in controlling melanoma proliferation. Citation Format: Yuuki Iida, Aaron Ciechanover, Diego M. Marzese, Keisuke Hata, Matias Bustos, Shigeshi Ono, Jinhua Wang, Matthew P. Salomon, Kevin Tran, Yelena Kravtsova-Ivantsiv, Gordon B. Mills, Michael A. Davies, Dave S.B. Hoon. Epigenetic regulation of KPC1 ubiquitin ligase has a regulatory role on the NF-κB pathway in metastatic melanoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3541.