BACKGROUND: Chromosomal translocations between distinct gene loci are now recognized as a molecular hallmark of prostate cancer. More than 50% of all primary prostate cancers harbour an androgen induced TMPRSS2-ERG gene fusion. Recently, it has been noted that advanced prostate cancers have genomic re-arrangements that disrupt the DNA mismatch repair gene MSH2. To date it is unknown whether translocations in MSH2 occur via the same mechanism as TMPRSS2 and if they are androgen induced.
AIMS: To investigate MSH2 loss in a patient cohort and identify the frequency of translocation events involving MSH2. To use cell based assays to define the affect of androgens on the frequency of MSH2 gene translocations.
METHODS and RESULTS: Whole genome sequencing was conducted on a cohort of 7 prostate cancer patients, one patient was found to have a fusion gene incorporating MSH2. Validation was conducted on a cohort of 99 recurrent and 90 non-recurrent prostate cancer patients to investigate the presence of functional MSH2 protein by immunohistochemistry (IHC). 6 of our recurrent patients were found to have no staining whereas all non-recurrent patients showed staining. Additionally, 23 recurrent patients and only 5 non-recurrent patients were observed to have weak MSH2 staining. Multiplex ligation-dependent probe amplification (MLPA), and a novel PCR based targeted sequencing assay “HEPtad” were performed on the patients that showed no staining identifying copy number variation and break points. A break-apart fluorescence in situ hybridisation (FISH) assay was then applied to identify MSH2 translocations in all low/negative MSH2 patient samples, identifying an additional 7 patients with translocations in the MSH2 gene. We also used this FISH assay to investigate the effect androgens on the frequency of breaks in the MSH2 gene for LAPC4, PC3 and VCAP cell lines.