Dysregulation of CELF4 splicing factor in pancreatic neuroendocrine tumors enhances aggressiveness and alters mTOR pathway and everolimus response

Abstract

Abstract Background Pancreatic neuroendocrine tumors (PanNETs) comprise a highly heterogeneous group of rare tumors, with growing incidence. Recent molecular analyses provided a precise picture of their genomic and epigenomic landscape. Splicing dysregulation is increasingly regarded as a novel cancer hallmark influencing all key tumor features. In this context, we have previously demonstrated that splicing machinery is markedly dysregulated in various cancers, including PanNETs. Here, we aimed to elucidate the molecular features and functional implications pertaining to one of the most altered splicing factors in PanNETs, CELF4. Methods CELF4 expression levels were determined in a cohort of 20 PanNET patients, comparing tumor and non-tumoral adjacent tissue, used as reference. RNA-Seq dataset was analyzed to explore CELF4-linked interrelations among clinical features, gene expression, and splicing event profiles. Two PanNET model cell lines, BON-1 and QGP-1, were employed to assess CELF4 function in vitro, including a detailed mTOR phospho-antibody array, and in vivo in BON-1-xenografted mice. Results PanNETs display markedly upregulated CELF4 expression levels, which closely associate with relevant malignancy features, specific expression of key tumor players (e.g., TP53), and distinct splicing event profiles. Functionally, modulation of CELF4 expression influenced PanNET cell lines proliferation in vitro, while CELF4 silencing in vivo reduced BON-1 xenograft tumor growth. Interestingly, CELF4 silencing enhanced the antiproliferative effect of the mTOR inhibitor everolimus in PanNET cells. Furthermore, detailed analysis of this core signaling pathway under CELF4 silencing showed changes in phosphorylation of the molecular components of the mTOR pathway. Conclusions Our results demonstrate that the splicing factor CELF4 is dysregulated in PanNETs, where it can influence tumor development and aggressiveness, likely by modulating mTOR pathway. These novel findings invite to explore in further detail this splicing factor as actionable therapeutic target in PanNETs.