REV-ERBβ is the prominent variant in various cancer cells. (a) REV-ERBα and REV-ERBβ relative expression in breast cancer BT-474 and primary human mammary epithelial HMEC cells was determined by quantitative reverse transcriptase–PCR (qRT–PCR). GAPDH expression was used as normalizer and the REV-ERBα relative expression was set to 1. Shown as mean±s.e.m., n=6. **P<0.01 and ***P<0.001, β versus α variant. (b) BT-474 and HMEC cells were circadian synchronized by dexamethasone (DEX) treatment for 2 h and the relative expression of REV-ERBα and REV-ERBβ was evaluated at the indicated post-treatment time points (circadian time=CT). CT8 has been chosen as the first point for the analysis to avoid the interference of the DEX response in the early time of synchronization.20 (c and d) The expression of REV-ERBα (c) and REV-ERBβ (d) in BT-474, SK-BR-3, MDA-MB-361 and MCF-7 breast cancer cells relative to their levels in normal HMEC cells was determined by qRT–PCR. GAPDH expression was used as the normalizer and the REV-ERB variant relative expression in HMEC cells was set to 1. Shown as mean±s.e.m., n=6. ***P<0.001, cancer versus normal HMEC cells. ###P<0.001, ERBB2-negative MCF-7 versus ERBB2-positive BT-474, SK-BR-3 and MDA-MB-361 cells. (e) Relative abundance of REV-ERBα and REV-ERBβ in non-cancer human mammary epithelial HMEC cells and in breast cancer cell lines with a different ERBB2 and ER status was evaluated by qRT–PCR. Presented as mean of the percentage of each isoform expression contribution to the total REV-ERBs expression (n=6, s.e.m.<3%). The ERBB2 and ER status of each cell line is indicated at the right. (f) Relative abundance of REV-ERBα and REV-ERBβ in liver, prostate, melanoma and colon cancer cell lines. (g) Relative abundance of REV-ERBα and REV-ERBβ in the OriGene Healthy tissues cDNA collection, which contains cDNA of various tissues pooled from multiple healthy individuals of different ethnicity to avoid detection of individual differences. (h) Relative abundance of REV-ERBα and REV-ERBβ in OriGene breast tumor cDNA samples. Information on age, ethnicity, tissue of origin/finding, ERBB2 and ER status are reported for each sample. Dashed line refers to the REV-ERBα percentage in normal tissue.