Epigenetic regulation of the ITGB4 gene in prostate cancer

Examination of epigenetic changes at the ITGB4 gene promoter reveals altered methylation at different stages of prostate tumour progression and these changes may, in part, explain the complex patterns of gene expression of this integrin observed. Transcriptional re-programming perturbs expression of cell adhesion molecules and underpins metastatic tumour cell behaviour. Decreasing expression of the cell adhesion molecule ITGB4, which encodes the beta subunit of the integrin, alpha6 beta4 (α6β4), has been correlated with increased tumour aggressiveness and metastasis in multiple tumour types including prostate cancer. Paradoxically, in vitro studies in tumour cell models demonstrate that ITGB4 mediates cell mobility and invasion. Herein we examined whether transcriptional re-programming by methylation influenced ITGB4 gene expression at different stages of prostate cancer progression. Bisulphite sequencing of a large CpG island in the ITGB4 gene promoter identified differentially methylated regions in prostate cancer cell lines representing a localised tumour (22Rv1), lymph node metastasis (LNCaP), and a bone metastasis (PC-3). The highest levels of methylation were observed in the CpG island surrounding the ITGB4 transcription start site in PC-3 cells, and this observation also correlated with higher gene expression of ITGB4 in these cells. Furthermore, PC-3 cells expressed two distinct transcripts, using an alternate transcription start site, which was not detected in other cell lines. In prostate tumour biopsy samples, patterns of methylation across the ITGB4 promoter were similar overall in matched primary and metastatic samples (n = 4 pairs), with a trend toward loss of methylation at specific sites in metastatic lesions.