Role of Lecithin: Retinol Acyltransferase (LRAT)-Mediated Esterification of Vitamin A in Regulating Human Breast Cancer Cell Proliferation and Differentiation

摘要

To understand the molecular mechanisms that mediate Lecithin:Retinol Acyltransferase (LRAT) transcription by Retinoic Acid (RA) in normal human mammary epithelial cells versus breast carcinoma cells, the authors isolated and characterized the promoter region of the human LRAT gene and tested its activity in normal mammary epithelial cells versus human breast carcinoma cells. Meanwhile, to determine if retinoic acid response gamma (RAR gamma) is involved in the regulation of LRAT gene expression, they tested LRAT mRNA levels in Wt and RAR gamma -/- F9 cells, an epithelial type of cell, which can synthesize retinyl esters. The RT-PCR analysis indicated that LRAT expression was lost in the MDA-MB-231 breast cancer cells. Surprisingly, they did not observe an RA-associated increase in LRAT mRNA levels in the HMEC cell line in culture. By using the MatInspector V2.2 computer program, they identified two conserved half-sites separated by four nucleotides(DR-4), as well as a DR-5 RARE in the 5' flanking region of the LRAT promoter region. They isolated the 2.3-kb 5'-flanking region of the human LRAT gene. The luciferase activity of this promoter region in MDA-MB-231 cells was one-sixth of that in HMEC cells at 48 hours, suggesting that this region harbors cis-elements contributing to the loss of LRAT expression in human breast cancer cells. RA treatment increases LRAT mRNA levels in F9 Wt cells at late times (72 hours). There was no apparent difference in the LRAT mRNA levels detected between the F9 Wt cells and F9 RAR gamma -/- cells, indicating that RAR gamma is not involved in the transcriptional regulation of the human LRAT gene.