Apolipoprotein M increases the expression of vitamin D receptor mRNA in colorectal cancer cells detected with duplex fluorescence reverse transcription-quantitative polymerase chain reaction.

Apolipoprotein M (ApoM) and the vitamin D receptor (VDR) are apolipoproteins predominantly presenting in high-density lipoprotein (HDL) and a karyophilic protein belonging to the steroid­thyroid receptor superfamily, respectively. Previous studies have demonstrated that ApoM and VDR are associated with cholesterol metabolism, immune and colorectal cancer regulation. In order to investigate whether ApoM affected the expression of VDR in colorectal cancer cells, a single­tube duplex fluorescence reverse transcription­quantitative polymerase chain reaction (RT­qPCR) system was developed to simultaneously detect the mRNA levels of VDR and GAPDH in HT­29 cells overexpressing ApoM. The results demonstrated that the amplification products were confirmed as the specific fragment of VDR/GAPDH using the DNA sequencing instrument. The sensitivity, linear range, correlation coefficient, amplification efficiency, intra­assay and inter­assay coefficients of variation were 40 copies/µl, 4.00x101­4.00x105 copies/µl, 0.999, 92.42%, 0.09­0.34% and 0.32­0.65% for VDR, and 40 copies/µl, 4.00x101­4.00x105 copies/µl, 0.999, 98.07%, 0.19­0.43% and 0.40­0.75% for GAPDH, respectively. The results indicated that the expression of VDR mRNA was significantly higher in HT­29 cells overexpressing ApoM, compared with the negative control group (P<0.05). In conclusion, the current study successfully developed the single­tube duplex RT­qPCR to simultaneously detect VDR and GAPDH expression in colorectal cancer cells. The methodology results demonstrated that the duplex RT­qPCR system with high sensitivity and specificity could ensure the objectivity and credibility of the detection. The present study confirmed that ApoM significantly increased the expression of VDR in HT­29 cells. In addition, it was hypothesized that ApoM may be involved in antineoplastic activity via the upregulation of VDR expression, which may provide novel directions for the investigation of ApoM in cancer.

17ß-estradiol regulates the expression of apolipoprotein M through estrogen receptor α-specific binding motif in its promoter.

BACKGROUND: We have previously demonstrated that estrogen could significantly enhance expression of apolipoprotein M (apoM), whereas the molecular basis of its mechanism is not fully elucidated yet. To further investigate the mechanism behind the estrogen induced up-regulation of apoM expression. RESULTS: Our results demonstrated either free 17ß-estradiol (E2) or membrane-impermeable bovine serum albumin-conjugated E2 (E2-BSA) could modulate human apoM gene expression via the estrogen receptor alpha (ER-α) pathway in the HepG2 cells. Moreover, experiments with the luciferase activity analysis of truncated apoM promoters could demonstrate that a regulatory region (from-1580 to -1575 bp (-GGTCA-)) upstream of the transcriptional start site of apoM gene was essential for the basal transcriptional activity that regulated by the ER-α. With the applications of an electrophoresis mobility shift assay and a chromatin immunoprecipitation assay, we could successfully identify a specific ER-α binding element in the apoM promoter region. CONCULSION: In summary, the present study indicates that 17ß-estradiol induced up-regulation of apoM in HepG2 cells is through an ER-α-dependent pathway involving ER-α binding element in the promoter of the apoM gene.

[Apolipoprotein M expression in human colorectal cancer tissues and its clinicopathological relevance].

OBJECTIVE: To investigate the mRNA and protein expression levels of apolipoprotein M (apoM) in the human colorectal cancer tissues, and to explore its clinical relevance. METHODS: Real-time PCR was carried out to determine the mRNA expression levels both in cancer tissue and its adjacent normal tissue from 20 patients with colorectal cancer. Immunohistochemistry was also carried out to determine the protein levels in 23 colorectal biopsy samples (7 normal mucosa, 6 inflammatory mucosa and 10 polyp tissues) and 20 cases of colorectal cancer tissues as well as the adjacent normal tissues. RESULTS: Real-time PCR result showed that apoM mRNA level in the colorectal cancer tissues was significantly lower than that in their adjacent normal tissues (0.05±0.01 vs. 0.19±0.05, P<0.05). ApoM mRNA level in colorectal cancer tissues was statistically significant higher in the patients with lymph node metastasis as compared to the patients without lymph node metastasis (P<0.01). The median value of apoM protein in cancer tissues was 5.50, which was significantly lower than that in the adjacent normal tissues (10.5, P<0.05), inflammatory mucosa tissues (9.75, P<0.05), polyp tissues (11.0, P<0.01) and normal mucosa (10.5, P<0.05). No significant association was observed between the apoM protein level and the clinicopathological parameters of patients. CONCLUSIONS: Both apoM mRNA and protein expression levels in colorectal cancer tissues are significantly decreased in contrast to normal and benign colorectal tissues. The apoM mRNA expression in colorectal cancer tissues is closely associated with nodal metastasis.