NSW increased risk of breast cancer in women who carried the heterozygote genotype of CRY2rs2292912 (OR = 1.98, 95% CI = 1.14-3.44) or carried at least one minor allele of RORA rs1482057 (OR = 2.20, 95% CI = 1.10-4.37).
Out of 17 genes investigated, 15 were found to be significantly associated with the risk of cancer: four genes were shared by all three malignancies (ARNTL, CLOCK, RORA and RORB), two by breast and lung cancer (CRY1 and CRY2) and three by prostate and lung cancer (NPAS2, NR1D1 and PER3), whereas four genes were specific for lung cancer (ARNTL2, CSNK1E, NR1D2 and PER2) and two for breast cancer (PER1, RORC).
Our data mining in TCGA breast cancer cohort (TCGA-BRCA) showed that the luminal A subtype of breast cancer had the highest CRY2 expression, while the basal-like subtype had the lowest CRY2 expression.
These findings suggest that the core circadian gene CRY2 is associated with breast cancer progression and prognosis, and that knockdown of CRY2 causes the epigenetic dysregulation of genes involved in cancer-relevant pathways, which provide further evidence supporting a role of the circadian system in breast tumorigenesis.
Associations between seven polymorphisms in circadian genes (CLOCK, NPAS2, ARTNL, PER2 and CRY2), genes of melatonin biosynthesis and signaling (AANAT and MTNR1B) and breast cancer were analyzed with conditional logistic regression models, adjusted for potential confounders for 1022 cases and 1014 controls.
We also observed a lower risk of breast cancer in carriers of the CRY2 CC genotype who were ER-positive than in those who were ER-negative (OR = 0.15, 95% CI = 0.04-0.67).
We silenced CRY2 in breast cancer cell lines (MCF-7) using small-interfering oligos (siRNA) and measured the impact of CRY2 knockdown on a number of cancer-relevant parameters.