Novel ATPase of SNF2-like Protein Family Interacts with Androgen Receptor and Modulates Androgen-dependent Transcription

Nuclear receptors, including the androgen receptor (AR), regulate target cell transcription through interaction with auxiliary proteins to modify chromatin structure. We describe herein a novel AR-interacting protein, termed ARIP4, that has structural features typical of the SNF2-like protein family. With regard to the Snf2 domain, the closest homolog of ARIP4 is the ATRX protein. ARIP4 is a nuclear protein and comprises 1466 amino acids. It interacts with AR in vitro and in cultured yeast and mammalian cells. ARIP4 can be labeled with 8-azido-[γ-(32)P]ATP and exhibits DNA-dependent ATPase activity. Like several ATP-dependent chromatin remodeling proteins, ARIP4 generates superhelical torsion within linear DNA fragments in an ATP-dependent manner. With a stably integrated target promoter, ARIP4 elicits a modest enhancement of AR-dependent transactivation. In transient cotransfection assays, ARIP4 modulates AR function in a promoter-dependent manner; it enhances receptor activity on minimal promoters, but does not activate more complex promoters. ARIP4 mutants devoid of ATPase activity fail to alter DNA topology and behave as trans-dominant negative regulators of AR function in transient assays.

核受体（Nuclear receptors）包括雄激素受体（androgen receptor, AR），可通过与辅助蛋白相互作用以改变染色质结构，从而调控靶细胞的转录过程。本文报道了一种被命名为ARIP4的新型AR互作蛋白，其具备SNF2样蛋白家族典型的结构特征。就Snf2结构域而言，ARIP4的最近同源物为ATRX蛋白。ARIP4属于核蛋白，全长包含1466个氨基酸，可在体外、培养的酵母及哺乳动物细胞中与AR发生相互作用。ARIP4可被8-azido-[γ-(32)P]ATP标记，并展现出依赖DNA的ATP酶活性。与诸多依赖ATP的染色质重塑蛋白类似，ARIP4能够以ATP依赖的方式在线性DNA片段内产生超螺旋扭转力。在搭载稳定整合靶启动子的体系中，ARIP4可轻度增强AR依赖的反式激活活性。在瞬时共转染实验中，ARIP4以启动子依赖的方式调控AR功能：其可在最小启动子上增强受体活性，但无法激活更为复杂的启动子。缺失ATP酶活性的ARIP4突变体无法改变DNA拓扑结构，且在瞬时实验中可作为AR功能的反式显性负调控因子发挥作用。