Dach1-Variant 4 Plays an Oncogenic Role and Promotes Radioresistance in Prostate Cancer

Background: Human Dachshund homologue 1 (DACH1) is involved in carcinogenesis with opposite roles reported in different tumor types. Four alternatively spliced transcripts encoding different DACH1 isoforms were described but their specific role in human cancers is still unknown. Prostate cancer (PCa) is a heterogeneous disease with a very wide variability, so there is yet a relevant need to find new diagnostic and therapeutic biomarkers to make a safe clinical evaluation. It is well known that the differential expression of protein isoforms can induce distinct transcriptional programs with opposing effects on tumor progression and therapy. Thus, in this study we aimed to correlate the functional role of DACH1 with its splicing variants expression in PCa.Methods: The expression and functional role of DACH1 splicing variants in PCa were investigated using tumor (PC3) and normal (RWPE-1) cell lines, patient biopsies and TCGA dataset. Flow-cytometry, western blots and RT-qPCR were used for in vitro molecular characterization; invasion, adhesion, clonogenic assays and cell cycle analysis for functional characterization. Immunohystochemistry and western blot were performed on human PCa biopsies.Results: RT-qPCR and Western Blot revealed that DACH1-positive PC3 cells predominantly expressed DACH1 variant 4 (DACH1-v4), whereas RWPE-1 cells mostly expressed DACH1 variant 3. Stable DACH1-v4 overexpression enhanced the transformed phenotype of PC3 cells by inducing proliferation, colony formation, invasion ability, epithelial to mesenchymal transition. Given its intrinsic radioresistance, PCa frequently recurs after radiotherapy. Of note, DACH1-v4-overexpressing PC3 cells displayed higher radioresistant behavior. Overexpression of DACH1-v4 also transformed RWPE-1 cells to oncogenic phenotype, suggesting a pro-oncogenic role for this specific isoform. PCa biopsies analysis showed DACH1 nuclear staining enhanced throughout the increase of the tumor grade. Remarkably, tumor glands were found to express a long DACH1 variant, while normal prostate tissue expressed the short DACH1 isoform, in line with data from TCGA-PRAD analysis and our data in RWPE-1 cells. Conclusions: Our findings highlight the oncogenic role of DACH1-v4 in PCa and suggest that the longer DACH1 variants could be associated to pro-tumor function, while the shortest DACH1 variant would perform tumor suppression. The expression of specific DACH1 isoforms could represent a novel diagnostic/prognostic marker in PCa.