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- [␥-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 promoterdependent 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.
INTRODUCTIONThe androgen receptor (AR) belongs to the superfamily of nuclear receptors that are ligand-activated transcription factors capable of regulating transcription of genes containing appropriate response elements, usually within or around the proximal promoter regions (Beato et al., 1995;Quigley et al., 1995;Perlmann and Evans, 1997). After hormone binding, the receptors associate with their cognate DNA motifs and modulate transcription initiation. Nuclear receptors may interact directly with the basal transcription factors associated with RNA polymerase II, such as TFIIB (Ing et al., 1992;Blanco et al., 1995;Hadzic et al., 1995), TFIIF (McEwan and Gustafsson, 1997), and TFIIH (Lee et al., 2000), or elicit their actions indirectly via auxiliary regulatory proteins, called coactivators and corepressors (Torchia et al., 1998;Freedman, 1999;McKenna et al., 1999;Glass and Rosenfeld, 2000).DNA is folded in the nucleus into a tight chromatin structure that often renders important regulatory sequences inaccessible for sequence-specific transcription factors, including steroid receptors (Kingston et al., 1996;Näär et al., 2001). As a consequence, different chromatin-modifying complexes are required to counteract this repressive effect (Bjö rklund et al., 1999;Kingston and Narlikar, 1999;Lemon and Freedman, 1999;Vignali et al., 2000). The protein complexes can be classified into two main categories: 1) ATP-dependent chromatin-remodeling complexes, which use the energy of ATP hydrolysis to alter the association of histones with DNA; and 2) complexes that alter chromatin by covalent modification of its components. These modifications include histone acetylation, methylation, phosphorylation, and ADP-ribosylation. Yeast SWI/SNF was the first ATP-dependent complex shown to facilitate the function of gene regulatory proteins in a...