FOSL1 promotes cholangiocarcinoma via transcriptional effectors that could be therapeutically targeted.

BACKGROUND AND AIMS Cholangiocarcinoma (CCA) is a neoplasia of the biliary tract driven by genetic, epigenetic and transcriptional mechanisms. Here, we investigated the role of the transcription factor FOSL1, as well as its downstream transcriptional effectors, in the development and progression of CCA. METHODS FOSL1 was investigated in human CCA clinical samples. Genetic inhibition of FOSL1 in human and mouse CCA cell lines was performed in in vitro and in vivo models using constitutive and inducible shRNAs. Conditional FOSL1 ablation was done using a genetically engineered mouse (GEM) model of CCA (mutant KRAS and Trp53 knockout). Follow-up RNA and ChIP sequencing analyses were carried out and validation of downstream targets using genetic and pharmacological inhibitory approaches was done. RESULTS An inter-species analysis of FOSL1 in CCA was conducted. First, FOSL1 was found highly upregulated in human and mouse CCA, and associated with poor patients' survival. Pharmacological inhibition of different signalling pathways in CCA cells converged on the regulation of FOSL1 expression. Functional experiments showed that FOSL1 is required for cell proliferation and cell cycle progression in vitro, and for tumour growth and tumour maintenance in vivo using both orthotopic and subcutaneous xenograft models. Likewise, FOSL1 genetic abrogation in a GEM model of CCA extended mice survival by decreasing the oncogenic potential of transformed cholangiocytes. RNA and ChIP sequencing studies identified direct and indirect transcriptional effectors such as HMGCS1 and AURKA, whose genetic and pharmacological inhibition phenocopied FOSL1 loss. CONCLUSIONS Our data illustrate the functional and clinical relevance of FOSL1 in CCA and unveil potential targets amenable to pharmacological inhibition that could serve for the implementation of novel therapeutic strategies. LAY SUMMARY Understanding the molecular mechanisms involved in CCA development and progression stands as a critical step for the development of novel therapies. Through an inter-species approach, this study provides evidence of the clinical and functional role of the transcription factor FOSL1 in CCA. Moreover, it unveils FOSL1 downstream effectors that are susceptible to pharmacological inhibition, thus providing new opportunities for therapeutic intervention.