Long Noncoding Rna Ovaal Promotes Melanoma Cell Proliferation Through Translational Suppression Of P27

Abstract Evading apoptosis and limitless replicative potential are two hallmarks of malignant cells. Here we report that melanoma cells surviving the induction of apoptosis by TNF-related apoptosis-inducing ligand (TRAIL) or the Mcl-1 inhibitor UMI-77 have even higher proliferative potential, and that this is associated with the increased expression of the long noncoding RNA (lncRNA) OVAAL which competes with p27 mRNA for binding to polypyrimidine tract binding protein 1 (PTBP1) and thus represses p27 mRNA translation. Prolonged exposure to TRAIL or Mcl-1 resulted in stable melanoma cell populations with increased proliferation activity. Comparative RNA-seq analysis identified OVAAL as the most significantly upregulated lncRNA in melanoma cells resistance to TRAIL and Mcl-1. ShRNA knockdown of OVVAL reversed the increased proliferative potential of resistant cells, and also inhibited proliferation in a subset of parental melanoma cell lines that constitutively expressed relatively high levels of OVAAL. RNA pulldown followed by Mass Spectrometry analysis revealed that among proteins that were physically associated with OVAAL was a protein called PTBP1 that bound to and enhanced the activity of the internal ribosomal entry site (IRES) in the 5' untranslated region (5'-UTR) of p27 mRNA. Indeed, OVAAL knockdown resulted in an increase in the association between PTBP1 and p27 IRES leading to upregulation of the p27 protein, whereas overexpression of OVAAL caused reduction in binding of PTBP1 to the IRES of p27. Furthermore, co-knockdown of PTBP1 abolished upregulation of p27 triggered by OVAAL knockdown. These results suggest that OVAAL competes with p27 mRNA for binding to PTBP1 and thus inhibits p27 expression and promotes cell proliferation. This was substantiated by binding assays using in vitro-synthesized biotin-labelled OVAAL, p27 IRES and purified PTBP1 in a cell-free system. Our results showed that the increased c-Myc activity was responsible for upregulation of OVAAL in melanoma cells selected for resistance to apoptosis induced by TRAIL or UMI-77. Collectively, these results identify the expression of OVAAL as an important mechanism promoting melanoma cell proliferation, with potential implications for targeting OVAAL in combination with apoptosis-inducing therapeutics in the treatment of melanoma. Citation Format: YUNA YUAN ZHANG, Xu Guang Yan, Margaret Farrelly, Hamed Yari, Yuchen Feng, Ting La, Hessam Tabatabaee, Lei Jin, Xu Dong Zhang. Long noncoding RNA OVAAL promotes melanoma cell proliferation through translational suppression of p27 [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 2451.