A SNP in Steroid Receptor Coactivator-1 Disrupts a GSK3β Phosphorylation Site and Is Associated with Altered Tamoxifen Response in Bone

• Published in: Molecular endocrinology (Baltimore, Md.) Md.), 2012-02, Vol.26 (2), p.220-227
• Main Authors: Hartmaier, R. J, Richter, A. S, Gillihan, R. M, Sallit, J. Z, McGuire, S. E, Wang, J, Lee, A. V, Osborne, C. K, O'Malley, B. W, Brown, P. H, Xu, J, Skaar, T. C, Philips, S, Rae, J. M, Azzouz, F, Li, L, Hayden, J, Henry, N. L, Nguyen, A. T, Stearns, V, Hayes, D. F, Flockhart, D. A, Oesterreich, S
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Amino Acid Substitution; Antineoplastic Agents, Hormonal - adverse effects; Antineoplastic Agents, Hormonal - therapeutic use; Bone Demineralization, Pathologic - chemically induced; Bone Demineralization, Pathologic - genetics; Bone Density - drug effects; Breast Neoplasms - prevention & control; Cell Line, Tumor; Clinical Trials as Topic; Female; Genetic Association Studies; Glycogen Synthase Kinase 3 - metabolism; Glycogen Synthase Kinase 3 beta; Humans; Molecular Sequence Data; Nuclear Receptor Coactivator 1 - genetics; Original Research; Phosphorylation; Polymorphism, Single Nucleotide; Protein Processing, Post-Translational; Protein Stability; Receptors, Estrogen - agonists; Receptors, Estrogen - metabolism; Sequence Analysis, DNA; Tamoxifen - adverse effects; Tamoxifen - therapeutic use
• ISSN: 0888-8809; 1944-9917
• DOI: 10.1210/me.2011-1032

The coregulator steroid receptor coactivator (SRC)-1 increases transcriptional activity of the estrogen receptor (ER) in a number of tissues including bone. Mice deficient in SRC-1 are osteopenic and display skeletal resistance to estrogen treatment. SRC-1 is also known to modulate effects of selective ER modulators like tamoxifen. We hypothesized that single nucleotide polymorphisms (SNP) in SRC-1 may impact estrogen and/or tamoxifen action. Because the only nonsynonymous SNP in SRC-1 (rs1804645; P1272S) is located in an activation domain, it was examined for effects on estrogen and tamoxifen action. SRC-1 P1272S showed a decreased ability to coactivate ER compared with wild-type SRC-1 in multiple cell lines. Paradoxically, SRC-1 P1272S had an increased protein half-life. The Pro to Ser change disrupts a putative glycogen synthase 3 (GSK3)β phosphorylation site that was confirmed by in vitro kinase assays. Finally, knockdown of GSK3β increased SRC-1 protein levels, mimicking the loss of phosphorylation at P1272S. These findings are similar to the GSK3β-mediated phospho-ubiquitin clock previously described for the related coregulator SRC-3. To assess the potential clinical significance of this SNP, we examined whether there was an association between SRC-1 P1272S and selective ER modulators response in bone. SRC-1 P1272S was associated with a decrease in hip and lumbar bone mineral density in women receiving tamoxifen treatment, supporting our in vitro findings for decreased ER coactivation. In summary, we have identified a functional genetic variant of SRC-1 with decreased activity, resulting, at least in part, from the loss of a GSK3β phosphorylation site, which was also associated with decreased bone mineral density in tamoxifen-treated women.