Associations of two-pore domain potassium channels and triple negative breast cancer subtype in The Cancer Genome Atlas: systematic evaluation of gene expression and methylation.

OBJECTIVES

It is unclear whether 2-pore domain potassium channels are novel molecular markers with differential expression related to biologically aggressive triple-negative type breast tumors. Our objective was to systematically evaluate associations of 2-pore domain potassium channel gene expression and DNA methylation with triple-negative subtype in The Cancer Genome Atlas invasive breast cancer dataset. Methylation and expression data for all fifteen 2-pore domain potassium family genes were examined for 1040 women, and associations with triple-negative subtype (vs. luminal A) were evaluated using age/race adjusted generalized-linear models, with Bonferroni-corrected significance thresholds. Subtype associated CpG loci were evaluated for functionality related to expression using Spearman's correlation.

RESULTS

Overexpression of KCNK5, KCNK9 and KCNK12, and underexpression of KCNK6 and KCNK15, were significantly associated with triple-negative subtype (Bonferroni-corrected p < 0.0033). A total of 195 (114 hypomethylated and 81 hypermethylated) CpG loci were found to be significantly associated with triple-negative subtype (Bonferroni-corrected p < 8.22 × 10). Significantly negatively correlated expression patterns that were differentially observed in triple-negative vs. luminal A subtype were demonstrated for: KCNK2 (gene body: cg04923840, cg13916421), KCNK5 (gene body: cg05255811, cg18705155, cg09130674, cg21388745, cg00859574) and KCNK9 (TSS1500: cg21415530, cg12175729; KCNK9/TRAPPC9 intergenic region: cg17336929, cg25900813, cg03919980). CpG loci listed for KCNK5 and KCNK9 all showed relative hypomethylation for probability of triple-negative vs. luminal A subtype. Triple-negative subtype was associated with distinct 2-pore domain potassium channel expression patterns. Both KCNK5 and KCNK9 overexpression appeared to be functionally related to CpG loci hypomethylation.