Frans-retinoic acid receptor

The physiological hormone for the RARs is all-frans-retinoic acid RA 221 and that for the RXRs is its geometric isomer, 9-czs-retinoic acid (9-czs-RA 222) [320]. However, these polyolefinic hormones are of only limited use in elucidating the precise biological roles of each receptor family. Synthetic ligands that specifically activate only the RXR or RAR hormonal pathway and which cannot be converted into forms that activate the other pathway would be of much greater use in this regard. 

Figure 4 Model of atRA biogeneration in mammals. REH, retinyl ester hydrolase (e.g., ES4 and ES10) TTR, transthyretin RAR-RXR, the heterodimer of retinoic acid receptors with retinoid X receptors atRCHO, all-frans-relinal atROH, all-frans-retinol CRBP(I), cellular retinol binding protein, type I LRAT, lecithin retinol acyltransferase SRBP, semm retinol binding protein. CRBP(I), CRABP(I), and CRABP(II) have been placed in the same cell for simplicity. This does not necessarily occur in vivo.

Figure 2.6. Interactions of all-frans- and 9-cw-retinoic acids (and other active retinoids) with retinoid receptors. COUP, chicken ovalbumin upstream promoter.

Sonneveld E, van den Brink CE, van der Leede BM, Schulkes RK, Petkovich M, van der Burg B, and van der Saag PT (1998) Human retinoic acid (RA) 4-hydroxylase (CYP26) is highly specific for all-frans-RA and can be induced through RA receptors in human breast and colon carcinoma cells. Cell Growth and Differentation 9,629-37. 

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