title: Ubiquitinated or sumoylated retinoic acid receptor alpha determines its characteristic and interacting model with retinoid X receptor alpha in gastric and breast cancer cells.
abstract: Retinoic acid receptor alpha (RARalpha) plays an important role in mediating all-trans retinoic acid (ATRA) signals. In this study, we found that ATRA up-regulated RARalpha mRNA and protein expression in gastric cancer BGC-823 cells. However, in breast cancer MCF-7 cells it down-regulated RARalpha protein expression with no effect on its RARalpha mRNA. Immunoprecipitation/Western blot analysis showed that, although sumoylated and ubiquitinated RARalpha existed simultaneously in both cancer cell lines, ATRA exerted different regulatory effects on sumoylation and ubiquitination of RARalpha. In MCF-7 cells, ATRA treatment enhanced the ubiquitination of RARalpha and the subsequent degradation of RARalpha through the ubiquitin/proteasome pathway. This resulted in a reduction in the DNA binding activity of RARalpha/retinoid X receptor alpha (RXRalpha) heterodimer, the separation of RXRalpha from RARalpha and the translocation of RXRalpha from the nucleus to the cytoplasm. By contrast, in BGC-823 cells, ATRA augmented sumoylation, not ubiquitination, of RARalpha. The stability of sumoylated RARalpha was significantly stronger than in non-sumoylated RARalpha. These results also showed an increase in the DNA binding activity of the RARalpha/RXRalpha heterodimer and the stability of nuclear localization of this heterodimer, which normally facilitates the ATRA signal transduction. In conclusion, our results reveal a novel mechanism for the regulation of RARalpha-dependent signal transduction through the ubiquitin/proteasome pathway in breast cancer cells and the sumoylation pathway in gastric cancer cells.
authors.affiliation: Key Laboratory of the Ministry of Education for Cell Biology and Tumor Cell Engineering, School of Life Sciences, Xiamen University, Xiamen 361005, Fujian Province, China.
authors.forename: Qiao
authors.initials: Q
authors.lastname: Wu
authors.forename: Xiao-feng
authors.initials: XF
authors.lastname: Lin
authors.forename: Xiao-feng
authors.initials: XF
authors.lastname: Ye
authors.forename: Bing
authors.initials: B
authors.lastname: Zhang
authors.forename: Zhong
authors.initials: Z
authors.lastname: Xie
authors.forename: Wen-jin
authors.initials: WJ
authors.lastname: Su
mesh_terms: D001943:Breast Neoplasms / Q000378:metabolism*; D045744:Cell Line, Tumor; D019281:Dimerization; D005260:Female; D006801:Humans; D025821:Polyubiquitin / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D011499:Protein Processing, Post-Translational; D018168:Receptors, Retinoic Acid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000072482:Retinoic Acid Receptor alpha; D047490:Retinoid X Receptor alpha / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D025842:SUMO-1 Protein / Q000378:metabolism*; D013274:Stomach Neoplasms / Q000378:metabolism*; D014212:Tretinoin / Q000378:metabolism
chemical_list: D061988:Proteasome Inhibitors; C000607071:RARA protein, human; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D047490:Retinoid X Receptor alpha; D025842:SUMO-1 Protein; D025821:Polyubiquitin; D014212:Tretinoin; D046988:Proteasome Endopeptidase Complex