DEFINITION
Retinoic acid is a metabolite of vitamin A (retinol) that mediates part of the functions of vitamin A required for growth and development.
![](http://www.nature.com/onc/journal/v25/n38/images/1209679f3.gif)
The more active forms are all-trans-RA and 7-cis-RA
SYNTHESIS AND TURNOVER
![](https://external-content.duckduckgo.com/iu/?u=http%3A%2F%2Fblogs.uw.edu%2Fni2%2Ffiles%2F2014%2F03%2FRA-homeostasis.png&f=1&nofb=1)
![](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fmedia.springernature.com%2Ffull%2Fspringer-static%2Fimage%2Fart%253A10.1186%252F2045-3701-2-11%2FMediaObjects%2F13578_2011_Article_52_Fig2_HTML.jpg&f=1&nofb=1)
![](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.researchgate.net%2Fpublication%2F221755976%2Ffigure%2Ffig1%2FAS%3A305504761991168%401449849419335%2FMetabolism-of-vitamin-A-retinol-to-all-trans-retinoic-acid-RA-and-the-mechanism-of.png&f=1&nofb=1)
![](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.researchgate.net%2Fprofile%2FEun-Jung-Rhee%2Fpublication%2F228072448%2Ffigure%2Ffig1%2FAS%3A202899176071168%401425386341949%2FThe-chemical-structures-of-retinoids_Q640.jpg&f=1&nofb=1)
![](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.researchgate.net%2Fprofile%2FKazunari_Sei%2Fpublication%2F231589894%2Ffigure%2Ffig1%2FAS%3A393518519472147%401470833534834%2FSchematic-Representation-of-the-Metabolism-of-Retinoids-and-Activation-of-RAR-Signaling.png&f=1&nofb=1)
![](https://external-content.duckduckgo.com/iu/?u=https%3A%2F%2Fwww.molfunction.com%2Fimages%2Frxr-rar.jpg&f=1&nofb=1)
![](http://www.nature.com/ng/journal/v31/n1/images/ng877-I1.gif)
The main enzymes involved in RA metabolism are
- the alcohol dehydrogenase ALDH1 (AL1A1_HUMAN, Retinal dehydrogenase 1) e ALDH2 (ALDH2_HUMAN, Aldehyde dehydrogenase, mitochondrial)
- the cytochrome P450 Cyp26 whose main function is to degrade endogenous all-trans retinoic acid (Retinoid metabolism: a balancing act, 2002)
Kegg's Pathways
Autocrine and/or paracrine effects
Retinoic acid in the development, regeneration and maintenance of the nervous system, 2007
![](http://www.nature.com/nrg/journal/v9/n7/images/nrg2340-i1.jpg)
Retinoic acid in development: towards an integrated view, 2008
CELLULAR FUNCTIONS
cellular localization,
![](http://www.igbmc.fr/recherche/Dep_BCD/Eq_PDoll/images/Box2.gif)
Vi sono due isomeri dell’RA biologicamente attivi: il trans-RA e il 9-cis-RA. (more info) L’RA si lega a due proteine citosoliche CRABP I e CRABP II. La prima è espressa ubiquitariamente mentre la seconda quasi esclusivamente a livello cutaneo.
Il complesso RA-CRBP trasloca nel nucleo e lega il retinoid-dependent nuclear receptor; questo recettore esiste in due forme: RAR e RXR entrambe appartenenti alla famiglia dei recettori nucleari per gli ormoni e in grado di agire come fattori di trascrizione.
biological function
![](http://img504.imageshack.us/img504/5938/meccvitaiq5.jpg)
REGULATION
DIAGNOSTIC USE
Effect of 9-cis-Retinoic Acid on Growth and RXR Expression in Human Breast Cancer Cells, 1995
- Our results show that: (1) the growth of ER+/RA-sensitive breast cancer cells is inhibited by treatment with 9-cis-RA by blocking entry into S phase; (2) both ER+/RA-sensitive and ER-/RA-resistant breast cancer cell lines express RXR-α and RXR-β mRNAs but not RXR-γ however, levels of these transcripts did not correlate with the RA response; and (3) levels of RXR-α and RXR-β mRNA were not significantly altered following treatment with either all-trans-RA or 9-cis-RA. These results suggest that the mechanism responsible for the retinoid sensitivity of breast cancer cells does not involve transcriptional modulation of the RXRs by RA.