Functional analysis of the promoter of the beta-microseminoprotein gene MSMB demonstrates the importance of a single nucleotide polymorphism in prostate cancer susceptibility

Two recent genome-wide association studies (GWAS) have independently identified a prostate cancer susceptibility locus on chromosome 10q11.2. The most significant single-nucleotide polymorphism (SNP) marker reported by both studies, rs10993994, is 57 bp centromeric of the first exon of the MSMB gene, which encodes beta-microseminoprotein (prostatic secretory protein 94, PSP94). This gene is a promising candidate gene for prostate cancer susceptibility because the protein, which is a member of immunoglobulin binding factor family, is already under investigation as a prostate cancer biomarker. To further explore the role of the MSMB/PSP94 locus on prostate cancer, we have performed fine-mapping using highly correlated tag SNP approach across the region defined by two independent GWAS with replication studies. After genotyping 13 tag SNPs from a ~65kb region of LD flanking rs10993994 SNPs in 6,118 prostate cancer cases and 6,105 controls of European origin from the Cancer Genetic Markers of Susceptibility (CGEMS) project, the T allele of rs10993994 remained the most strongly associated marker with prostate cancer risk. In follow-up functional analyses, promoter constructs with the C allele of rs10993994 display strong promoter activity. In electrophoretic mobility shift assays, the C allele of rs10993994 binds to the CREB transcription factor, whereas the T allele does not. Analysis of tumor cell lines including the NCI 60 panel indicated significantly higher levels of MSMB/PSP94 gene expression in cell lines with a CC or CT genotype compared to cell lines with a TT genotype. These findings were specific to the alleles of rs10993994 and were not observed for other SNPs determined by sequence analysis of the proximal promoter. MSMB/PSP94 expression is reported to be reduced during the progression of prostate cancer, and lower expression of MSMB/PSP94 is associated with the risk of prostate cancer. The present study suggests that rs10993994 is functionally important and perhaps accounts for the association with prostate cancer susceptibility. Together our mapping studies and functional analyses implicate regulation of expression of MSMB as the plausible mechanism accounting for the association identified at this locus.