Abstract 4494: Tumor suppressive role of ZFP36L1 by suppressing HIF1α and Cyclin D1 in bladder and breast cancer

Abstract

Abstract AU-rich mRNAs are a class of mRNAs that contains AU-rich elements (AREs) motifs in their 3’UTR. The half-life and turnover of AU-rich mRNAs are tightly regulated by AREs-binding proteins, such as Zinc finger protein 36 C3H type-like 1 (ZFP36L1). ZFP36L1 is one of the RNA-binding proteins (RBPs), which consists of two tandemly repeated zinc finger motifs that specifically recognize AREs motifs and mediate mRNAs decay. However, our knowledge on role of ZFP36L1 in breast and bladder cancers and its downstream targets remains poorly elucidated. Here, we hypothesized that ZFP36L1 might degrade oncogenic mRNAs transcripts, thus leading to suppression of tumorigenesis. Our analysis of in silico data revealed that ZFP36L1 is significantly mutated or downregulated in a variety of cancers. The high proportion of inactivation mutation pattern as well as the Mutsig result suggest that it may act as an unappreciated tumor suppressor. Lower ZFP36L1 expression correlated with reduced survival in patients. Forced expression of ZFP36L1 markedly reduced cellular proliferation, invasiveness and migration in vitro, as well as tumor growth in vivo. In addition, microarray and RNA-seq data analysis showed that several important cancer-related candidates such as IL8 and HIF1α were significantly downregulated. Overexpression of ZFP36L1 reduced HIF1α mRNA and protein expression. Similarly, HIF1α forced expression also inhibited ZFP36L1 mRNA and protein, suggesting a feedback loop of HIF1α and ZFP36L1. Dual luciferase reporter assays and RNA Electro-mobility Shift Assay (REMSA) showed that only wild type ZFP36L1, but not different mutants of ZFP36L1, was able to bind directly and to degrade a HIF1α 3’UTR construct that contains AU-rich regions. Meanwhile, mRNA pull down assay demonstrated that ZFP36L1 protein recognized cell-cycle related transcripts. Overexpression of ZFP36L1 led to reduction of Cyclin D1 and phospho-Rb in protein expression. Furthermore, SILAC data unveiled interesting binding partners of ZFP36L1. Collectively, our findings propose that ZFP36L1 might have a critical tumor suppressive role in breast and bladder cancer by negatively regulating mRNA whose protein products cooperatively promote hypoxia and transition into S phase of cell cycle. Augmenting ZFP36L1 function might disable the cell cycle and proliferation of aggressive bladder tumors. Citation Format: Xin Yi Loh, Ling Wen Ding, H. Phillip Koeffler. Tumor suppressive role of ZFP36L1 by suppressing HIF1α and Cyclin D1 in bladder and breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 4494. doi:10.1158/1538-7445.AM2017-4494