Polymorphisms in the CRK gene and their association with breast cancer risk

Background

Recent findings suggest an important influence of the GH1/IGF1 axis in the development of breast cancer. By binding to its receptor, IGF-1 stimulates numerous downstream signaling proteins resulting in the regulation of cell proliferation, differentiation and apoptosis [1]. One member of this pathway is CRK (v-crk sarcoma virus CT10 oncogene homolog), which is tyrosine phosphorylated upon IGF-1 stimulation. CRK has been found to be overexpressed in various human tumor tissues and cell lines [2]. However, little is known about alterations in the genomic sequence of this gene.

Methods

We sequenced the promoter and the coding region of the CRK gene in a small sample set of 23 breast cancer samples. We confirmed a C to A polymorphism at nucleotide position 49 with a synonymous amino acid change at Arg17, which was in nearly 100% linkage to the promoter polymorphism C-289A, and we identified a novel polymorphic duplication of 22 bp in the promoter region. In the further analyses we used a TaqMan allelic discrimination assay for the Arg17 polymorphism and a fluorescent fragment analysis to detect the duplication in a sample set of 352 Polish familial breast cancer cases and 485 matched controls. We determined the genotype and haplotype frequencies and calculated the odds ratios with 95% confidence intervals.

Results

We did not observe any differences in the allele or genotype frequencies between the cases and controls for the duplication polymorphism. For the Arg17 polymorphism, the allele frequency of the A allele was slightly decreased among the cases compared with the controls (52.3% vs 56.0%, respectively), but the difference was not statistically significant. In the haplotype analysis, we observed a protective effect for the carriers of the Arg17 A and the duplication alleles (odds ratio = 0.17, 95% confidence interval = 0.03-0.76, P = 0.007).

Conclusions

CRK is a member of the GH1/IGF-1 pathway, whose members are often found to be overexpressed in human tumors. The, to our knowledge, novel 22 bp duplication in the promoter region results in multiplication of various putative transcription factor binding sites. This may lead to an altered expression of the CRK gene. In combination with the Arg17 A allele it showed a protective effect. The Arg17 polymorphism was in nearly 100% linkage with a polymorphism in the promoter, which also might have an effect on transcription. However, a functional analysis is needed to investigate the effect of these polymorphisms on the expression.