Abstract 2530: An analysis of correlative interactions between Plk1, Notch1 and FoxM1 in melanoma

Melanoma is one of the most aggressive forms of skin cancer, and existing therapies have not been effective in managing this neoplasm. Therefore, a deeper understanding of the mechanisms of melanoma development/progression is required. The goal of this study was to define the potential interactions between several key melanoma-linked proteins, namely Polo-like kinase 1 (Plk1; a cell cycle regulator involved in G2/M transition), Notch (Notch1; a type I transmembrane protein that decides cell fate during development), and forkhead box M1 (FoxM1; a transcription factor regulating S and G2/M phases of cell cycle) in human melanoma. Previously, we have shown that Plk1 is overexpressed in melanoma, and its inhibition results in G2/M phase arrest and apoptosis in multiple melanoma cells. Recent studies have shown that both Notch1 and FoxM1 may be involved in the pathogenesis of certain cancers, including melanoma. In this study, employing an in-house human tissue microarray (TMA) coupled with high-throughput, multispectral Vectra scanning and inForm analysis, we analyzed 126 clinical tissue specimens of normal skin and localized cutaneous melanoma. The TMA was co-immunostained for Plk1, Notch1, FoxM1, and the melanoma biomarker S100, followed by Vectra scanning and analyses with inForm software. Using this system, we determined the levels of Plk1, Notch1, and FoxM1 in both the nucleus and cytoplasm of melanoma cells which were positive for S100 staining. By applying statistical tools of Wilcoxon Signed-Rank Test and Pearson9s Correlation Coefficient in R programming, we found that while all the proteins are detected in both nucleus and cytoplasm, FoxM1 and Notch1 are enriched in the nucleus, and Plk1 is enriched in the cytoplasm. Visualization of the correlation coefficients on a heat-map showed that all 3 sets of proteins (Plk1:Notch1, Plk1:FoxM1, and Notch1:FoxM1) are positively correlated, with Plk1:Notch1 having the strongest correlation, and FoxM1 having a weaker correlation with the other two proteins. The associative relationship between Plk1 and Notch1 leads to the hypothesis that Plk1 and Notch1 may be positively correlated in melanoma. We further studied how Breslow thickness, a measure of melanoma aggressiveness, is related to Plk1, Notch1 and FoxM1. By analyzing the TMA cores with available clinical data, we found a positive correlation between Breslow thickness and Notch1, as well as Plk1. Interestingly, although Breslow thickness was significantly correlated with FoxM1 in the nucleus, no correlation was found in the cytoplasm, suggesting that FoxM1 levels may be independent of Plk1 and Notch1. Overall, our study found novel correlative interactions between Plk1 and Notch1 in melanoma, which may have relevance to melanoma progression. Additional studies are needed to validate our findings and dissect the possible interaction between Plk1 and Notch1 during melanoma development and progression. Citation Format: Shengqin Su, Chandra K. Singh, Mary A. Ndiaye, Vijayasaradhi Setaluri, Nihal Ahmad. An analysis of correlative interactions between Plk1, Notch1 and FoxM1 in 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 2530.