Molecular Cloning and Characterization of CAPER, a Novel Coactivator of Activating Protein-1 and Estrogen Receptors

Abstract

Transcriptional coactivators either bridge transcription factors and the components of the basal transcription apparatus and/or remodel the chromatin structures. We isolated a novel nuclear protein based on its interaction with the recently described general coactivator activating signal cointegrator-2 (ASC-2). This protein CAPER (for coactivator of activating protein-1 (AP-1) and estrogen receptors (ERs)) selectively bound, among the many transcription factors we tested, the AP-1 component c-Jun and the estradiol-bound ligand binding domains of ER␣ and ER␤. Interestingly, CAPER exhibited a cryptic autonomous transactivation function that becomes activated only in the presence of estradiol-bound ER. In cotransfections, CAPER stimulated transactivation by ER␣, ER␤, and AP-1. Thus, CAPER may represent a more selective transcriptional coactivator molecule that plays a pivotal role for the function of AP-1 and ERs in vivo in conjunction with the general coactivator ASC-2.The activation protein-1 (AP-1) 1 transcription factors are immediate early response genes involved in a diverse set of transcriptional regulatory processes (for a review see Ref. 1). The AP-1 complex consists of a heterodimer of a Fos family member and a Jun family member. This complex binds the consensus DNA sequence (TGAGTCA) (termed AP-1 sites) found in a variety of promoters. The Fos family contains four proteins (c-Fos, Fos-B, Fra-1, and Fra-2), whereas the Jun family is composed of three proteins (c-Jun, Jun-B, and Jun-D). Fos and Jun are members of the basic region-leucine zipper (bZIP) family of sequence-specific dimeric DNA-binding proteins (1). The C-terminal half of the bZIP domain is amphipathic, containing a heptad repeat of leucines that is critical for the dimerization of bZIP proteins, whereas the N-terminal half of the long bipartite helix is the basic region that is responsible for the sequence-specific DNA binding.The nuclear receptor superfamily is a group of ligand-dependent transcriptional regulatory proteins that function by binding to specific DNA sequences named hormone-response elements in the promoters of target genes (reviewed in Ref.2). The superfamily includes receptors for a variety of small hydrophobic ligands such as steroids, triiodothyronine, and retinoids as well as a large number of related proteins that do not have known ligands, referred to as orphan nuclear receptors. The C terminus of the ligand binding domain of these proteins harbors an essential ligand-dependent transactivation function, activation function 2 (AF2), whereas the N terminus of many nuclear receptors often includes AF1.Genetic studies implicated that transcription coregulators (or cofactors) with no specific DNA binding activity are essential components of transcriptional regulation, which ultimately led us to identify a series of coregulatory proteins (for reviews, see Refs. 3 and 4). They appear to function by either remodeling chromatin structures and/or acting as adapter molecules between transcription factors and the components of the b...

CAPER, a novel regulator of human breast cancer progression

“…19 CAPER is identical to the human protein HCC1.4, which was previously described as a novel nuclear autoantigen in human hepatocarcinoma. 19,21 CAPER was also shown to be related to known splicing factors such as the U2 auxiliary factor (U2AF65) and the poly(U)-binding-splicing factor-60 (PUF60).…”

“…19 Using glutathione-S-transferase (GST)-pulldown and luciferase reporter assays, Jung et al (2002) demonstrated that CAPER directly interacted with ERα/β and c-Jun and potently stimulated their transcriptional activity in vitro. 19 However, the role of CAPER in human breast cancer pathogenesis remained unknown.…”

“…19 Using glutathione-S-transferase (GST)-pulldown and luciferase reporter assays, Jung et al (2002) demonstrated that CAPER directly interacted with ERα/β and c-Jun and potently stimulated their transcriptional activity in vitro. 19 However, the role of CAPER in human breast cancer pathogenesis remained unknown. Interestingly, using the PM2000 AQUA automated quantitative analysis system (HistoRx Inc) and a human breast cancer tissue microarray consisting of 84 invasive ductal carcinomas (IDCs) and 20 normal breast tissue samples, we recently reported that CAPER protein expression was significantly elevated in human breast cancer specimens, as compared with normal breast tissue.…”

Unmasking the U2AF homology motif family: a bona fide protein–protein interaction motif in disguise

“…2F; Loerch et al 2014). These three proteins function in alternative splicing (Page-McCaw et al 1999;Lallena et al 2002;Dowhan et al 2005;Hastings et al 2007;Huang et al 2012); PUF60 and CAPERα also are coactivators of transcription (Liu et al 2000(Liu et al , 2001Jung et al 2002;Dowhan et al 2005;Dutta et al 2008). Other UHM-containing proteins participate in related pathways.…”

The Nuclear Hormone Receptor Coactivator NRC Is a Pleiotropic Modulator Affecting Growth, Development, Apoptosis, Reproduction, and Wound Repair

“…In addition to CBP, NRC has been reported to associate with a number of other factors, including CoAA, PIMT, CAPER, and NIF-1 (27,28,40,71). Unlike NIF-1, CAPER, PIMT, and CoAA each contain RNA binding motifs.…”