title: Phosphorylated retinoid X receptor alpha loses its heterodimeric activity with retinoic acid receptor beta.
abstract: A malfunction in retinoid X receptor (RXR) alpha due to phosphorylation is associated with the development of hepatocellular carcinoma. However, the precise mechanisms by which phosphorylated RXRalpha loses its physiological function remain unclear. In the present study we examined whether phosphorylation of RXRalpha affects its dimeric activity. Fluorescence resonance energy transfer studies and immunoprecipitation assays showed that the physical interaction between RXRalpha and retinoic acid receptor beta was impaired when 293T cells were transfected with phosphomimic mutant RXRalpha (T82D/S260D), whereas this interaction was activated at a level similar to wild-type RXRalpha-transfected cells when the cells were transfected with an unphosphorylated mutant RXRalpha (T82A/S260A). Treating the T82A/S260A-transfected cells with retinoid resulted in a significant increase in the transcriptional activities of the retinoic acid receptor responsive element and RXR responsive element promoters, whereas these transcriptional activities did not increase in the T82D/S260D-transfected cells. Transfection with T82A/S260A enhanced both the inhibition of cell growth and the induction of apoptosis caused by retinoid, although the T82D/S260D-transfected cells lost their responsiveness to retinoid. Moreover, transfection with T82A/S260A caused an inhibition of cell growth and a reduction of colony-forming ability in soft agar in HuH7 human hepatocellular carcinoma cells. These findings suggest that phosphorylation of RXRalpha abolishes its ability to form homodimers and heterodimers with RXR and retinoic acid receptor beta, thus resulting in the loss of cell growth control and the acceleration of cancer development. In conclusion, the inhibition of RXRalpha phosphorylation and the restoration of its original function as a master regulator of nuclear receptors might therefore be an effective strategy for controlling cancer cell growth.
authors: Department of Medicine, Gifu University Graduate School of Medicine, Gifu, 501-1194, Japan.
authors: Kotaro
authors: K
authors: Yoshimura
authors: Yoshinori
authors: Y
authors: Muto
authors: Masahito
authors: M
authors: Shimizu
authors: Rie
authors: R
authors: Matsushima-Nishiwaki
authors: Masataka
authors: M
authors: Okuno
authors: Yukihiko
authors: Y
authors: Takano
authors: Hisashi
authors: H
authors: Tsurumi
authors: Soichi
authors: S
authors: Kojima
authors: Yukio
authors: Y
authors: Okano
authors: Hisataka
authors: H
authors: Moriwaki
mesh_terms: D017209:Apoptosis; D002455:Cell Division; D002460:Cell Line; D019281:Dimerization; D031541:Fluorescence Resonance Energy Transfer; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D007668:Kidney; D010766:Phosphorylation; D010957:Plasmids; D018168:Receptors, Retinoic Acid / Q000235:genetics* / Q000378:metabolism; D015183:Restriction Mapping; D000072482:Retinoic Acid Receptor alpha; D047490:Retinoid X Receptor alpha / Q000235:genetics* / Q000378:metabolism; D014162:Transfection
chemical_list: C000607071:RARA protein, human; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D047490:Retinoid X Receptor alpha