Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:1.17.1.4 (xanthine dehydrogenase)
 1,236 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The seeming impairment of retinoid metabolism in human breast tumor cells has been attributed to the lower expression of cellular retinol binding proteins (CRBPs), of alcohol/retinol dehydrogenases, or aldehyde/retinaldehyde dehydrogenases. In a previous study we indicated that xanthine dehydrogenase (XDH) is able to oxidize actively both all-trans-retinol (t-ROL) bound to the CRBP (holo-CRBP) and all-trans-retinaldehyde (t-RAL) to all-trans-retinoic acid (t-RA) in human mammary epithelial cells (HMEC). Since both XDH and CRBP are required for the biosynthesis of t-RA, we have inspected their bioavailability in both estrogen-responsive and nonresponsive human mammary epithelial cancer cells. The XDH activity, as assessed in the crude and purified extracts of both MCF7 and MDA-MB 231 cells by measuring the substrate t-RAL (that unlike t-ROL does not need CRBP), was 6 to 10 times lower than that previously encountered in normal HMEC. In addition, CRBP expression was absent in either cell line. Based on this preliminary evidence, we propose here that the low levels of XDH activity and the associated absence of CRBP in both MCF7 and MDA-MB 231 human breast cancer cells might be responsible for the retinoic acid deficiency observed in these cell model systems. This defect may be the crux of the impairment to stem cell differentiation and, hence, may be primarily implicated in human mammary carcinogenesis.
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PMID:Low levels of both xanthine dehydrogenase and cellular retinol binding protein are responsible for retinoic acid deficiency in malignant human mammary epithelial cells. 1925 Feb 15

The retinoic acid deficiency in breast tumour epithelial cells has been ascribed to an insufficient expression of either the enzyme(s) involved in its biosynthesis or the cellular retinol binding protein (CRBP) or both. In an attempt to define the mechanisms underpinning retinoic acid deficiency in these cell model systems, we have investigated the potential regulatory effect of oestrogen (17beta-estradiol) on one key player in retinoic acid biosynthesis, the xanthine dehydrogenase (XDH). This enzyme is consistently expressed and very active in non-malignant human mammary epithelial cells (HMEC), as opposed to tumour MDA-MB231 and MCF7 cells. In these latter two cell lines, as opposed to HMEC cells, we observe a residual ability of XDH to produce retinoic acid from retinaldehyde and the inability to use retinol, as a consequence of a deficit in CRBP. In addition, estradiol treatment of MDA-MB231 and MCF7 cells decreases protein expression and activity of the enzyme, with no modification of the mRNA transcript levels, eventually leading to deteriorate further retinoic acid production.
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PMID:Estradiol decreases xanthine dehydrogenase enzyme activity and protein expression in non-tumorigenic and malignant human mammary epithelial cells. 1969 77