Interactions between Activating Signal Cointegrator-2 and the Tumor Suppressor Retinoblastoma in Androgen Receptor Transactivation

Young-Hwa Goo,Soon-Young Na,Hao Zhang,Jianming Xu,Sunhwa Hong,Jaehun Cheong,Soo-Kyung Lee,Jae Woon Lee

doi:10.1074/jbc.m312563200

Abstract

Activating signal cointegrator-2 (ASC-2), a cancer-amplified transcription coactivator of nuclear receptors and numerous other transcription factors, was previously shown to contain two LXXLL motifs, each of which interacts with a distinct set of nuclear receptors. In this work, we showed that ASC-2 has an indirect, separate binding site for androgen receptor (AR). Interestingly, this region overlapped with the direct interaction interfaces with the tumor suppressor retinoblastoma (Rb). Although ASC-2 alone stimulated AR transactivation in cotransfections of HeLa cells, ectopic expression of Rb effected ASC-2 to act as a transcription coactivator of AR in Rb-null Saos2 cells. These results, along with the previous report in which AR was shown to directly interact with Rb (Yeh, S., Miyamoto, H., Nishimura, K., Kang, H., Ludlow, J., Hsiao, P., Wang, C., Su, C., and Chang C. (1998) Biochem. Biophys. Res. Commun. 248, 361-367), suggest that the AR-ASC-2 interactions in vivo may involve Rb. Thus, ASC-2 appears to contain at least three distinct nuclear receptor interaction domains.

Highlights

The nuclear receptor superfamily is a group of proteins that regulate, in a ligand-dependent manner, transcriptional initiation of target genes by binding to specific DNA sequences named hormone response elements
We showed that activating signal cointegrator-2 (ASC-2) has an indirect, separate binding site for androgen receptor (AR)
Transgenic mice overexpressing ASC-2 fragment DN1 but not DN1/m in which the LXXLL sequences were mutated to LXXAA to disable the receptor bindings were significantly impaired for many signaling pathways mediated by retinoic acid and other receptors, in which DN1 competitively blocked the interaction of these receptors with the full-length endogenous ASC-2 (14)

Summary

Introduction

The nuclear receptor superfamily is a group of proteins that regulate, in a ligand-dependent manner, transcriptional initiation of target genes by binding to specific DNA sequences named hormone response elements (reviewed in Ref. 1). Single cell microinjection of neutralizing antibodies against ASC-2 abolished transactivation by retinoic acid and other nuclear receptors that interact with ASC-2 (7). Along with the previous report in which AR was shown to directly interact with Rb (19), these results suggest that the AR-ASC-2 interactions in vivo could be mediated by Rb. Overall, these results suggest that 1) ASC-2 is likely an essential coactivator of AR, and 2) ASC-2 contains at least three distinct nuclear receptor-interacting domains.

Results

Conclusion