Lin Feng, Kolluri Siva Kumar, Chen Guo-quan, Zhang Xiao-kun
Burnham Institute, Cancer Center, La Jolla, California 92037, USA.
J Biol Chem. 2002 Jun 14;277(24):21414-22. doi: 10.1074/jbc.M201885200. Epub 2002 Apr 4.
Retinoids are therapeutically effective in the treatment of various cancers, and some of the therapeutic action of retinoids can be ascribed to their potent inhibition of AP-1 activity that regulates transcription of genes associated with cell growth. We recently reported that the expression of orphan receptor chicken ovalbumin upstream promoter-transcription factor (COUP-TF) plays a role in mediating the growth inhibitory effect of trans-retinoic acid (trans-RA) in cancer cells. To gain insight into the molecular mechanism by which COUP-TF regulates trans-RA activity, we evaluated the effect of COUP-TF on antagonism of AP-1 activity by trans-RA. Our results demonstrated a positive correlation between COUP-TF expression and the ability of trans-RA to inhibit AP-1 activity in various cancer cell lines. In transient transfection assay, expression of COUP-TF strongly inhibited tumor promoter 12-O-tetradecanoylphorbol-13-acetate-induced AP-1 transactivation activity and transactivation of c-Jun/c-Fos in both a trans-RA-dependent and -independent manner. In vitro studies demonstrated that the addition of COUP-TF inhibited c-Jun DNA binding through a direct protein-protein interaction that is mediated by the DNA binding domain of COUP-TF and the leucine zipper of c-Jun. Stable expression of COUP-TF in COUP-TF-negative MDA-MB231 breast cancer cells restored the ability of trans-RA to inhibit 12-O-tetradecanoylphorbol-13-acetate-induced c-Jun expression. The effect of COUP-TF in enhancing the trans-RA-induced antagonism of AP-1 activity required expression of retinoic acid receptors (RARs), since stable expression of COUP-TF in COUP-TF-negative HT-1376 bladder cancer cells, which do not express RARalpha and RARbeta, failed to restore trans-RA-induced AP-1 repression. Thus, COUP-TF, through its physical interaction with AP-1, promotes anticancer effects of retinoids by potentiating their anti-AP-1 activity.
维甲酸在多种癌症的治疗中具有治疗效果，维甲酸的一些治疗作用可归因于其对AP-1活性的强效抑制，而AP-1活性可调节与细胞生长相关基因的转录。我们最近报道，孤儿受体鸡卵清蛋白上游启动子转录因子（COUP-TF）的表达在介导反式维甲酸（trans-RA）对癌细胞的生长抑制作用中发挥作用。为深入了解COUP-TF调节反式维甲酸活性的分子机制，我们评估了COUP-TF对反式维甲酸拮抗AP-1活性的影响。我们的结果表明，在各种癌细胞系中，COUP-TF表达与反式维甲酸抑制AP-1活性的能力之间存在正相关。在瞬时转染实验中，COUP-TF的表达以反式维甲酸依赖性和非依赖性方式强烈抑制肿瘤启动子12-氧十四烷酰佛波醇-13-乙酸酯诱导的AP-1反式激活活性以及c-Jun/c-Fos的反式激活。体外研究表明，添加COUP-TF通过由COUP-TF的DNA结合结构域和c-Jun的亮氨酸拉链介导的直接蛋白质-蛋白质相互作用抑制c-Jun与DNA的结合。在COUP-TF阴性的MDA-MB231乳腺癌细胞中稳定表达COUP-TF可恢复反式维甲酸抑制12-氧十四烷酰佛波醇-13-乙酸酯诱导的c-Jun表达的能力。COUP-TF增强反式维甲酸诱导的AP-1活性拮抗作用的效果需要视黄酸受体（RARs）的表达，因为在不表达RARα和RARβ的COUP-TF阴性HT-1376膀胱癌细胞中稳定表达COUP-TF未能恢复反式维甲酸诱导的AP-1抑制。因此，COUP-TF通过与AP-1的物理相互作用，增强维甲酸的抗AP-1活性，从而促进维甲酸的抗癌作用。
