Nucleic Acids Research Advance Access originally published online on April 1, 2009
Nucleic Acids Research 2009 37(9):3110-3123; doi:10.1093/nar/gkp136
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Nucleic Acids Research, 2009, Vol. 37, No. 9 3110-3123
© 2009 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Molecular Biology |
CK1
modulates the transcriptional activity of ER
via AIB1 in an estrogen-dependent manner and regulates ER–AIB1 interactions
1Department of Medical Oncology, Imperial College London, Hammersmith Hospital Campus, Du Cane Road, London, W12 ONN, UK, 2Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA and 3Department of General-, Visceral- and Transplantation Surgery, University of Ulm, D 89075 Ulm, Germany
*To whom correspondence should be addressed. Tel: +44 208 7468295; Fax: +44 208 8461433; Email: g.giamas{at}imperial.ac.uk or j.stebbing{at}imperial.ac.uk
Received January 19, 2009. Revised February 13, 2009. Accepted February 18, 2009.
Oncogenesis in breast cancer often requires the overexpression of the nuclear receptor coactivator AIB1/SRC-3 acting in conjunction with estrogen receptor-
(ER). Phosphorylation of both ER and AIB1 has been shown to have profound effects on their functions. In addition, proteasome-mediated degradation plays a major role by regulating their stability and activity. CK1
, a member of the ubiquitous casein kinase-1 family, is implicated in the progression of breast cancer. In this study, we show that both ER and AIB1 are substrates for CK1 in vitro, and identify a novel AIB1 phosphorylation site (S601) targeted by CK1, significant for the co-activator function of AIB1. CK1 is able to interact with ER and AIB1 in vivo, while overexpression of CK1 in breast cancer cells results in an increased association of ER with AIB1 as confirmed by co-immunoprecipitation assays from cell lysates. Using an siRNA-based approach, luciferase reporter assays and qRT-PCR, we observe that silencing of CK1 leads to reduced ER transcriptional activity, despite increased ER levels, similarly to proteasome inhibition. We provide evidence that AIB1 protein levels are reduced by CK1 silencing, in an estradiol-dependent manner; such destabilization can be inhibited by pre-treatment with the proteasome inhibitor MG132. We propose that differing activities adopted by ER and AIB1 as a consequence of their interactions with and phosphorylation by CK1, particularly AIB1 stabilization, influence the transcriptional activity of ER, and therefore have a role in breast cancer development.