Song Liang-Nian, Herrell Roger, Byers Stephen, Shah Salimuddin, Wilson Elizabeth M, Gelmann Edward P
Department of Oncology, Lombardi Cancer Center, Georgetown University School of Medicine, Washington, D.C. 20007-2197, USA.
Mol Cell Biol. 2003 Mar;23(5):1674-87. doi: 10.1128/MCB.23.5.1674-1687.2003.
Beta-catenin is a multifunctional molecule that is activated by signaling through WNT receptors. beta-Catenin can also enhance the transcriptional activity of some steroid hormone receptors such as the androgen receptor and retinoic acid receptor alpha. Androgens can affect nuclear translocation of beta-catenin and influence its subcellular distribution. Using mammalian two-hybrid binding assays, analysis of reporter gene transcription, and coimmunoprecipitation, we now show that beta-catenin binds to the androgen receptor ligand-binding domain (LBD) and modulates the transcriptional effects of TIF2 and the androgen receptor N-terminal domain (NTD). In functional assays, beta-catenin bound to androgen receptor only in the presence of ligand agonists, not antagonists. Beta-catenin binding to the androgen receptor LBD was independent of and cooperative with the androgen receptor NTD and the p160 coactivator TIF2, both of which bind to the activation function 2 (AF-2) region of the androgen receptor. Different mutations of androgen receptor helix 3 amino acids disrupted binding of androgen receptor NTD and beta-catenin. beta-Catenin, androgen receptor NTD, and TIF2 binding to the androgen receptor LBD were affected similarly by a subset of helix 12 mutations, but disruption of two sites on helix 12 affected only binding of beta-catenin and not of TIF2 or the androgen receptor NTD. Mutational disruption of each of five LXXLL peptide motifs in the beta-catenin armadillo repeats did not disrupt either binding to androgen receptor or transcriptional coactivation. ICAT, an inhibitor of T-cell factor 4 (TCF-4), and E-cadherin binding to beta-catenin also blocked binding of the androgen receptor LBD. We also demonstrated cross talk between the WNT and androgen receptor signaling pathways because excess androgen receptor could interfere with WNT signaling and excess TCF-4 inhibited the interaction of beta-catenin and androgen receptor. Taken together, the data show that beta-catenin can bind to the androgen receptor LBD and modulate the effects of the androgen receptor NTD and TIF2 on transcription.
β-连环蛋白是一种多功能分子，可通过WNT受体信号传导被激活。β-连环蛋白还可增强某些类固醇激素受体的转录活性，如雄激素受体和视黄酸受体α。雄激素可影响β-连环蛋白的核转位并影响其亚细胞分布。我们通过哺乳动物双杂交结合试验、报告基因转录分析和免疫共沉淀，发现β-连环蛋白可与雄激素受体配体结合域（LBD）结合，并调节TIF2和雄激素受体N端结构域（NTD）的转录效应。在功能试验中，β-连环蛋白仅在存在配体激动剂而非拮抗剂的情况下与雄激素受体结合。β-连环蛋白与雄激素受体LBD的结合独立于雄激素受体NTD和p160共激活因子TIF2，且与之协同，二者均与雄激素受体的激活功能2（AF-2）区域结合。雄激素受体螺旋3氨基酸的不同突变破坏了雄激素受体NTD与β-连环蛋白的结合。螺旋12的一部分突变对β-连环蛋白、雄激素受体NTD和TIF2与雄激素受体LBD的结合影响相似，但螺旋12上两个位点的破坏仅影响β-连环蛋白的结合，而不影响TIF2或雄激素受体NTD的结合。β-连环蛋白犰狳重复序列中五个LXXLL肽基序的突变均未破坏其与雄激素受体的结合或转录共激活。T细胞因子4（TCF-4）的抑制剂ICAT以及E-钙黏蛋白与β-连环蛋白的结合也阻断了雄激素受体LBD的结合。我们还证明了WNT和雄激素受体信号通路之间存在相互作用，因为过量的雄激素受体可能干扰WNT信号传导，而过量的TCF-4会抑制β-连环蛋白与雄激素受体的相互作用。综上所述，数据表明β-连环蛋白可与雄激素受体LBD结合，并调节雄激素受体NTD和TIF2对转录的影响。
