Coordinated Regulation of AIB1 Transcriptional Activity by Sumoylation and Phosphorylation

Abstract

AIB1, a member of the steroid receptor coactivator (SRC) family that participates in gene transcriptional activation by nuclear receptors and other transcription factors, is required for animal growth and reproductive development and implicated in breast carcinogenesis. The mechanisms underlying the AIB1 pleiotropic functions are not fully understood and neither is the regulation of its activity. Here, we showed that AIB1 was a sumoylated protein and the sumoylation attenuated the transactivation activity of AIB1, which is in contrast to the sumoylation of its paralogs, GRIP1 and SRC-1. The transactivation activity of AIB1 is enhanced by its phosphorylation by several kinases, including mitogen-activated protein kinase. We demonstrated in this report that estrogen treatment led to an increased phosphorylation and decreased sumoylation of AIB1 and that the sumoylation coordinated with phosphorylation in regulating the transcriptional activity of AIB1, providing a mechanism for post-translational modifications in regulating the transcriptional output of AIB1.Nuclear receptors play critical roles in animal development and homeostasis through their bimodal function as repressors or activators of gene transcription (1). The repression and activation activity of nuclear receptors are determined by their association with corepressors and coactivators, respectively. Among the coactivators, the steroid receptor coactivator (SRC) 2 family is both necessary and sufficient for nuclear receptor-mediated gene activation as we previously demonstrated (2). The SRC family of coactivators includes three distinct but related p160 members: SRC-1, GRIP1 (or SRC-2), and AIB1 (also named RAC3, ACTR, SRC-3, or p/CIP in mice) (3-6). They share 40% overall sequence similarity, and they all contain, in the N terminus, a basic helix-loop-helix domain that is known for protein dimerization-DNA interaction as well as a Per-Arnt-Sim domain, which is known to be involved in protein-protein interaction. Three LXXLL motifs, also known as nuclear receptor boxes (for nuclear receptor binding), are centrally located in all three proteins (7-9). In the C terminus, the SRC proteins contain two activation domains, AD1 and AD2, which are associated with histone acetyltransferases (CREB-binding protein/p300 and pCAF) and coactivator-associated arginine methyltransferase 1, respectively, and function to modify the configuration of the chromatin structure (10, 11).Despite the structural similarities among the members of the SRC family of coactivators, evidence has been accumulated to suggest different physiological functions for SRC-1, GRIP1, and AIB1. Genetic studies with gene ablation showed that, although both male and female SRC1-null mice are viable and fertile, they exhibit partial resistance to several hormones, including estrogen, progestin, androgen, and thyroid hormones (12, 13). Elimination of GRIP1 impairs fertility in both male and female mice (14), and GRIP-null mice are protected against obesity and display enhanced adaptive thermogenesis, ...

SUMOylation-regulated Protein Phosphorylation, Evidence from Quantitative Phosphoproteomics Analyses

“…Meanwhile, evidence for phosphorylation-obstructed SUMO modification was also found. For example, phosphorylation of the AIB1 protein by the MAPK pathway was found to be inhibitory to its SUMO modification (14). These studies highlight the important regulatory mechanism for phosphorylation-modulated SUMOylation in regulating cellular events.…”

SYT-SSX1 (Synovial Sarcoma Translocated) Regulates PIASy Ligase Activity to Cause Overexpression of NCOA3 Protein

“…It is known that NCOA3 itself can also be modified through sumoylation (46), and sumoylation can compete with ubiquitination, if such modification occurs on the same lysine residue (37,38). Indeed, in rat1 3Y1 fibroblast cells, expression of SYT and SYT-SSX1 results in increased sumoylation of Ncoa3 (Fig.…”

Common variants in the UBC9 gene encoding the SUMO‐conjugating enzyme are associated with breast tumor grade

“…SUMO is also conjugated to coregulators of ERa and ERb, thereby modulating their ability to interact with the nuclear receptor and to activate transcription. [11][12][13] In addition, various components of the SUMO-conjugating machinery are upregulated in several malignancies: UBC9 in melanomas, ovarian cancer and lung adenocarcinomas, [14][15][16] the SUMO isopeptidase SENP1 in prostate cancer 17 and PIAS3 in breast, lung, prostate, colorectal and brain tumors. 18 By using MCF-7 human breast cancer cells overexpressing a dominant-negative mutant of UBC9 or wild type UBC9 in a mouse xenograft model it was shown that tumors expressing the UBC9 mutant exhibited reduced growth, whereas wild type UBC9 enhanced tumor growth.…”