Vitamin cellular retinoid-binding proteins

The specific role of vitamin A in tissue differentiation has been an active area of research. The current thinking, developed in 1979, involves initial dehvery of retinol by holo-B >V (retinol-binding protein) to the cell cytosol (66). Retinol is then ultimately oxidized to retinoic acid and binds to a specific cellular retinoid-binding protein and is transported to the nucleus. Retinoic acid is then transferred to a nuclear retinoic acid receptor (RAR), which enhances the expression of a specific region of the genome. Transcription occurs and new proteins appear during the retinoic acid-induced differentiation of cells (56). 

Soprano DR (1994) Serum and cellular retinoid binding proteins. In Vitamin Receptors Vitamins and Ligands in Cell Communication, K Daksbinamurti (ed.), pp. 1-27. Cambridge, UK Cambridge University Press. 

A Role for Vitamin A and the Cellular Retinoid-Binding Proteins in Differentiation. 115... 

B. Are Cellular Retinoid-Binding Proteins Necessary for Vitamin A Action ... 

E Andersson, C Bjorklind, H Torma, A Vahlquist. The metabohsm of vitamin A to 3,4-didehydroretinol can be demonstrated in human keratinocytes, melanoma cells and HeLa cells, and is correlated to cellular retinoid-binding protein expression. Biochim Biophys Acta 1224 349-354, 1994. 

Eppinger TM, Buck J, Hammerling U (1993) Growth control or terminal differentiation endogenous production and differential activities of vitamin A metabolites in HL-60 cqWs. J Exp Med 178 1995-2005 Herr F, Ong DE (1992) Differential interaction of lecithin-retinol acyltransferase with cellular retinoid-binding proteins. Biochemistry 31 6748-6755... 

Preformed vitamin A, most often in the form of retinyi ester, or carotenoids are subject to emulsification and mised micelle formation by the action of bile salts before being transported into the intestinal cell. Here the retinyi esters are moved across the mucosal membrane and hydrolyzed to retinol within the cell to then be reesterified by cellular retinol-binding protein II and packaged into chylomicra, which then enter the mesenteric lymphatic system and pass mto the systemic circulation. A small amount of the ingested retinoid is also converted into retinoic acid in the intestinal cell. The efficiency of absorption of preformed vitamin A is high at between 70% and 90%. ... 

Vitamin A absorbs UV light between 300 and 350 nm. After acute exposure to UVA or UVB a dose-dependent decrease of vitamin A was shown in mouse59 and humans.84 UV irradiation markedly reduced mRNA and protein of the nuclear retinoid receptors RARy and RXRa in humans and led to a near loss of retinoic acid induction of the RAR/RXR target genes and the cellular retinoic acid binding protein II thus effectively causing additionally a functional vitamin A deficiency.85... 

Retinoids are differentiation agents related to or derivative of vitamin A. They bind to a cellular protein that facilitates their transfer from the cytoplasm to the nucleus where they are believed to increase DNA, RNA, and protein synthesis and to affect cellular mitosis. 

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