Habano et al. BMC Cancer 2011, 11:81 http://www.biomedcentral.com/1471-2407/11/81 Page 4 of 10 Results Basal mRNA levels of the CYP3A4, PXR and VDR genes in the 6 colon cancer cell lines Real-time PCR analyses revealed that the basal levels of CYP3A4, PXR (exon 5-6), PXR (exon 1a-2) and VDR mRNA were heterogeneous among the 6 cell lines examined (Figure 2). The 6 cell lines were then classified into two groups (high or low expression cells) based on the basal level of PXR and CYP3A4 mRNA, because the 6 cell lines always showed either high PXR and CYP3A4 expression or low PXR and CYP3A4 expression. The levels of CYP3A4 and PXR transcripts on high expres- sion cells (LS180 and LoVo) were 7- to 35-fold and 40- to 5,000-fold higher than those on lower expression cells (Caco-2, HT29, HCT116 and SW48), respectively. These two groups also exhibited a difference in the basal level of the VDR transcript, although this differ- ence was not marked (3.5- to 6-fold). There was strong Figure 2 Basal expression profile of colon cancer cell lines. Basal levels of (a), PXR exon 5-6; (b), PXR exon 1a-2; (c), CYP3A4; and (d), VDR transcripts in LS180, LoVo, Caco-2, HT29, HCT116 and SW48 cells. The vertical axis indicates a relative transcript level (ratio to LS180 cells). The transcripts indicated by * (PXR exon 5-6 transcript in SW48 cells and CYP3A4 transcript in HCT116 cells) were not detected and we estimated the minimum detectable levels among gradually diluted calibration samples (0.00257 and 0.0399, respectively).