TGFß-induced lncRNA LINC00313 activates Wnt signalling and promotes cholangiocarcinoma progression
Cholangiocarcinoma (CCA) is a devastating liver cancer characterized by high aggressiveness and resistance to therapy, which results to poor prognosis. Signals imposed by oncogenic pathways, such as transforming growth factor ß (TGFß) frequently contribute to CCA development. In this study, we explored novel effectors of the TGFß pathway in CCA by gene expression profiling. We identified the long non-coding RNA LINC00313 as a novel target gene of TGFß signalling in CCA cells. TGFß induced LINC00313 expression in a TßRI/Smad-dependent manner. Subcellular fractionation showed that LINC00313 is a predominantly nuclear lncRNA. By integrating RNA-seq and ATAC-seq data from LINC00313 over-expressing cells, we observed that LINC00313 regulates the expression of several genes involved in the Wnt signalling pathway. As a proof of concept, we focused on the gene encoding transcription factor 7 (TCF7), a major effector that drives transcription of Wnt-target genes. LINC00313 gain of function resulted in increased TCF7 expression, while its loss of function diminished basal or TGFß-induced TCF7 expression levels. Interestingly, LINC00313 enhanced basal or chemically induced TCF/LEF-dependent transcriptional responses, promoted colony-forming capacities of CCA cells in vitro and accelerated tumor growth in vivo. We also report that genes associated with LINC00313 over-expression recapitulate poor prognosis human CCA associated with a reduced overall survival and KRAS mutations. To decipher the underlying molecular functions of LINC00313, we identified its interacting proteins by performing an unbiased RNA pull-down assay followed by mass spectrometry. We demonstrated that actin-like 6A (ACTL6A), a subunit of the SWI/SNF chromatin remodelling complex specifically binds to LINC00313 and impacts TCF7 expression and TCF/LEF signalling output. Thus, we propose a model whereby TGFß induces LINC00313, in order to regulate the expression of a subset of target genes, such as TCF7 possibly in co-operation with the SWI/SNF chromatin remodelling complex, via establishing direct interaction with ACTL6A. By regulating key genes of the Wnt pathway, LINC00313 fine-tunes Wnt/TCF/LEF-dependent transcriptional responses and boosts cholangiocarcinogenesis.