HIP1 mediates oncogenic transformation and cancer progression through STAT3 signalling

Background: Huntingtin-interacting protein 1 (HIP1) is an adaptor protein involved in transcriptional regulation and receptor-mediated endocytosis. Overexpression of HIP1 transforms cell and is associated with, increasing grades of prostate cancer (CaP) and poor patient outcomes. However, the precise mechanism for the role of HIP1 in prostate cancer progression remains unknown. Methods: Using a phospho-kinase antibody array we identified changes in signalling associated with HIP1 overexpression PNT1 cells. For validation Western blots were used together with knockdown or inhibitor treatments and phenotypic assays for cellular transformation. The cell line was xenografted to assess tumour growth. Gene expression microarray analysis of the cell line was used to identify perturbations in transcript levels. Results: Here we demonstrate cellular transformation and phenotypic effects of HIP1 overexpression in a benign prostate epithelial cell line to be dependent on STAT3 signalling. In vivo xenografts confirmed the cellular transformation phenotype. Gene expression analysis revealed serum protein GDF15 to be a marker of prostate cancer tumorigenesis in our model. We present a HIP1-STAT3-GDF15 axis in our pre-clinical model that mediates cellular transformation and tumorigenesis. Conclusion: Our findings provide a model defining the functional effects of increased HIP1 expression in prostate tumorigenesis and progression. This model implicates increased STAT3 signalling in HIP1- dependent prostate carcinogenesis and identifies GDF15 as a secreted factor supporting this process. The role of HIP1-STAT3-GDF15 signalling may extend to other epithelial cancers shown to overexpress HIP1; such as gliomas, colon and breast cancer where STAT3 is an emerging oncology drug target.