Abstract 3102: Phosphorylated and SUMO-deficient progesterone receptors transcriptionally up-regulate growth factor signaling pathway genes in breast cancer cells
Authors: Knutson Todd P. , Daniel Andrea R. , Lange Carol A. 
Published: June 2012

Abstract
Progesterone receptors (PRs) mediate proliferation in developing mammary tissue and are suspected to contribute to breast cancer progression. Elevated expression and activity of epidermal growth factor (EGF) receptor family members frequently occurs in advanced breast cancer and these receptors undergo extensive cross-talk with PR signaling. Growth factor-induced protein kinases (MAPK, CDK2) regulate PR post-translational modifications, such as phosphorylation, ubiquitination, and SUMOylation.
PR is phosphorylated at Ser294 in response to ligand-binding, EGF, or expression of activated downstream MAP kinases. PR Ser294 phosphorylation antagonizes ligand-induced PR SUMOylation at Lys388. SUMOylated transcription factors often interact with repressor complexes at promoter regions. Therefore, we hypothesized that growth factors prevent SUMO attachment to PR Lys388 via MAPK-induced phosphorylation of Ser294; this event provides a mechanism for PR derepression at genes important for increased proliferation and survival of aggressive breast cancer cells. We predict that SUMOylated PR and SUMO-deficient mutant receptors (K388R) will have different transcriptional consequences on selected cancer related gene promoters.
We developed inducible and constitutive models of PR expression in T47D human breast cancer cells. Regardless of model system, cells expressing SUMO-deficient mutant (K388R) PR exhibited increased proliferation and decreased apoptosis relative to cells expressing SUMOylated (wild type) PR. To explain these differences in proliferation and survival, we used microarrays to measure PR-induced changes in global gene expression. We found that SUMO-deficient, but not wild type PR, up-regulated tumor-promoting genes and repressed tumor suppressor genes. We investigated the mechanisms responsible for these transcriptional differences by chromatin immunoprecipitation (ChIP) assays. SUMO-deficient PR recruitment to the promoters of multiple genes expected to drive proliferation was favored over wild type PR. Gene Set Enrichment Analysis revealed that MAPK pathway genes were preferentially up-regulated by SUMO-deficient PR.
Our data suggest that aggressive cancers containing high kinase activities are driven in part by phospho- (deSUMOylated) PR. Consequently, phospho-PR acts in a feed-forward mechanism to transcriptionally up-regulate key components of the MAPK pathway, leading to increased cell proliferation and survival. Our work provides strong rationale for targeting growth factor receptor signaling pathways in combination with steroid hormone receptors, including PR, as part of targeted therapies for advanced breast cancer [NIH R01 CA12376 to C.A.L.; DOD BC093529 to T.P.K.].
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3102. doi:10.1158/1538-7445.AM2011-3102