p21WAF1/CIP1 is a common transcriptional target of retinoid receptors: pleiotropic regulatory mechanism through retinoic acid receptor (RAR)/retinoid X receptor (RXR) heterodimer and RXR/RXR homodimer.
The divergent response and the molecular mechanisms underlying the anti-cancer effects of retinoid X receptor (RXR) ligand (rexinoid) therapy are poorly understood. This study demonstrates that ligand-activated RXR homodimer facilitated G(1) arrest by up-regulation of p21 in vitro and in vivo but failed to induce G(1) arrest when p21 expression was blocked by p21 small interfering RNA. RXR ligand-dependent p21 up-regulation was transcriptionally controlled through the direct binding of RXR homodimers to two consecutive retinoid X response elements in the p21 promoter. Structural overlap of a retinoic acid response element with these retinoid X response elements led to a high affinity binding of retinoic acid receptor/RXR heterodimer to the retinoic acid response element, resulting in the prevention of RXR ligand-mediated p21 transactivation. These data show that p21 is a potential and novel molecular target for RXR ligand-mediated anti-cancer therapy and that the expression level of retinoic acid receptor and RXR in tumors may be crucial to induce p21-mediated cell growth arrest in RXR ligand therapy.
NCI, National Institutes of Health, Bethesda, Maryland 20892-4255, USA. Takemi.Tanaka@uth.tmc.edu
Takemi
T
Tanaka
Kwang S
KS
Suh
Angela M
AM
Lo
Luigi M
LM
De Luca
D000818:Animals; D002453:Cell Cycle; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D019281:Dimerization; D005260:Female; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D011485:Protein Binding; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D047488:Retinoid X Receptors / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors