Abstract 143: The role of microRNAs in mediating the oncogenic effect of Notch signaling in melanoma

Abstract

Abstract Purpose. Dysregulated Notch signaling has been connected with a variety of cancers, including melanoma. We previously demonstrated that aberrant Notch signaling is a crucial oncogenic promoter in driving melanoma development and progression. However, the molecular mechanism underlying the oncogenic effect of Notch signaling on melanoma progression remains largely unknown, and we hypothesized it might be mediated in part through regulating miRNAs. We sought to identify these Notch-regulated miRNAs. Methods. Notch-regulated specific miRNAs were identified by examining miRNA profiles in response to Notch activation and inhibition in melanoma cells using RT2-PCRArray. Enforced activation and suppression of the Notch pathway were achieved by transducing melanoma cells with viral vectors encoding activated Notch1 (NIC) and dominant-negative Mastermind-like 1 (DN-MAML1), respectively. The role of specific miRNAs in mediating the oncogenic effect of Notch was studied by testing whether alteration of miRNA expression could reverse the oncogenic effect of the Notch signaling on promoting melanoma cell growth, survival, and colony-formation in vitro. The potential targets of the Notch-regulated specific miRNAs were investigated by testing several known Notch targets, including MAPK, Akt, Mel-CAM, N-cadherin and β-catenin. Results. It was found that hsa-let-7b and hsa-let-7d miRNAs respond to Notch activation specifically in primary melanoma cells. Hsa-let-7b and hsa-let-7d were down-regulated 3.9-fold and 3.1-fold respectively when the Notch1 pathway was constitutively activated, whereas such down-regulation could be completely reversed when Notch activation was suppressed by DN-MAML1. Overexpression of hsa-let-7b or hsa-let-7d was able to antagonize the Notch activation-induced melanoma cell colony-formation on soft-agar, yet did not affect melanoma cell growth and survival in vitro. Both hsa-let-7b and hsa-let-7d appeared to specifically modulate the Notch-induced Akt activation in melanoma cells as phosphorylation of Akt was attenuated by overexpression of either hsa-let-7b or hsa-let-7d, while other known Notch targets were not affected. Conclusions. The hsa-let-7b and hsa-let-7d were identified as Notch-regulated specific miRNAs in primary melanoma cells. Both hsa-let-7b and hsa-let-7d are responsible for mediating, in part, the oncogenic effect of aberrant Notch signaling on promoting melanoma progression, presumably through modulating Akt activation. Our findings not only uncovered a novel mechanism underlying the oncogenic effect of the Notch signaling on promoting melanoma progression, but also provided potential novel targets for melanoma diagnosis, prognosis and therapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 143. doi:10.1158/1538-7445.AM2011-143