Associations of a polymorphism in the ornithine decarboxylase gene with colorectal cancer survival.

PURPOSE

Activity of ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis, is required for normal growth and is elevated in many cancers, including colorectal cancer. We examined associations of the +316 ODC1 single nucleotide polymorphism (SNP) with colorectal cancer-specific survival among colorectal cancer cases, and then investigated its functional significance in colon cancer cells.

EXPERIMENTAL DESIGN

The study included 400 incident stage I-III colorectal cancer cases from the population-based University of California Irvine Gene-Environment Study of Familial Colorectal Cancer (diagnosed from 1994 to 1996 with follow-up through March 2008). The primary outcome was colorectal cancer-specific survival dependent on ODC1 (rs2302615) genotype (GG versus GA/AA). In human colon cancer cell lines, ODC1 allele-specific binding of E-box transcription factors was determined via Western blotting and chromatin immunoprecipitation assays. ODC1 allele-specific promoter activity was determined using promoter constructs in combination with vectors expressing either the transcriptional activator c-MYC or the repressor MAD1.

RESULTS

Genotype-specific survival differences were observed among colorectal cancer cases: compared with cases with the ODC1 GG genotype (hazards ratio, 1; reference) the adjusted colorectal cancer-specific survival hazards ratio was 2.02 (95% confidence interval, 1.17-3.50) for ODC1 GA/AA cases (P = 0.012). In colon cancer cells, the ODC1 SNP, flanked by two E-boxes, predicts ODC1 promoter activity. The E-box activator c-MYC and repressors MAD1 and MAD4 preferentially bind to ODC1 minor A-alleles, compared with major G-alleles, in cultured cells.

CONCLUSIONS

These results have implications for conditional regulation of polyamine homeostasis and suggest a model in which the ODC1 SNP may be protective for colon adenoma recurrence and detrimental for survival after colon cancer diagnosis.