Direct channeling of retinoic acid between cellular retinoic acid-binding protein II and retinoic acid receptor sensitizes mammary carcinoma cells to retinoic acid-induced growth arrest.
Cellular retinoic acid-binding protein II (CRABP-II) is an intracellular lipid-binding protein that associates with retinoic acid with a subnanomolar affinity. We previously showed that CRABP-II enhances the transcriptional activity of the nuclear receptor with which it shares a common ligand, namely, the retinoic acid receptor (RAR), and we suggested that it may act by delivering retinoic acid to this receptor. Here, the mechanisms underlying the effects of CRABP-II on the transcriptional activity of RAR and the functional consequences of these effects were studied. We show that CRABP-II, a predominantly cytosolic protein, massively undergoes nuclear localization upon binding of retinoic acid; that it interacts with RAR in a ligand-dependent fashion; and that, in the presence of retinoic acid, the CRABP-II-RAR complex is a short-lived intermediate. The data establish that potentiation of the transcriptional activity of RAR stems directly from the ability of CRABP-II to channel retinoic acid to the receptor. We demonstrate further that overexpression of CRABP-II in MCF-7 mammary carcinoma cells dramatically enhances their sensitivity to retinoic acid-induced growth inhibition. Conversely, diminished expression of CRABP-II renders these cells retinoic acid resistant. Taken together, the data unequivocally establish the function of CRABP-II in modulating the RAR-mediated biological activities of retinoic acid.
Budhu
Anuradha S
AS
Division of Nutritional Sciences, Cornell University, Ithaca, New York 14853, USA.
Noy
Noa
N
D000818:Animals; D001693:Biological Transport, Active; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D019556:COS Cells; D002455:Cell Division / Q000187:drug effects; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008024:Ligands; D051379:Mice; D008954:Models, Biological; D018168:Receptors, Retinoic Acid / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D014212:Tretinoin / Q000378:metabolism* / Q000494:pharmacology*
D008024:Ligands; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; C082927:retinoic acid binding protein I, cellular; C082928:retinoic acid binding protein II, cellular; D014212:Tretinoin