PhosphoSer134 GR, TGF-β and 14-3-3-zeta cooperate to promote progression of Triple Negative Breast Cancer

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PROJECT SUMMARY/ABSTRACT Therapeutic options for triple-negative breast cancer (TNBC) are limited. This subtype of breast cancer (BC) lacks expression of molecules currently exploited for targeted therapy including steroid hormone receptors, estrogen receptor and progesterone receptor, as well as human epidermal growth factor 2 receptor. TNBC is the most aggressive, metastatic, and deadly form of BC, and it accounts for up to 40% of all BC cases. Notably, 15- 40% of TNBC patients express glucocorticoid receptor (GR). GR is part of the steroid hormone receptor superfamily and its functions in TNBC are poorly understood. GR proteins are heavily post-translationally modified via phosphorylation events. Phosphorylation of GR has a variety of effects on GR function, including altered interaction with cofactors and subsequent changes in the regulation of global gene expression. Specifically, we are interested in phosphorylation of GR on Ser134, a site that is uniquely induced by cellular stress stimuli but independently of ligand. Notably, phosphoSer134 GR is critical for the expression of PTK6, a protein tyrosine kinase that is implicated in advanced breast cancer phenotypes. Our preliminary data indicates that phosphoSer134 GR expression is greater in TNBC relative to other breast cancer subtypes. TGFβ is a cytokine associated with aggressiveness of TNBC. Recently, we discovered that TGFβ signaling leads to phosphorylation of GR on Ser134 and promotes its interaction with the scaffolding protein 14-3-3ζ. Understanding the basis of cooperation between TGFβ, GR and 14-3-3ζ and subsequent upregulation of PTK6, will allow us to target this signaling and transcriptional complex as a means to block tumor progression and metastasis. In Aim 1, we propose to test the requirement for 14-3-3ζ as potential driver of phosphoSer134 GR target gene regulation and cancer cell migration/invasion and survival in TNBC models. In Aim 2, we will demonstrate the oncogenic roles of PTK6 as driver of tumor progression to metastasis in vivo using mouse xenograft studies. The proposed research and training plans provide a rigorous program for successful completion of my M.D./Ph.D. degrees. Moreover, it will provide me with the fundamentals to become a successful academic surgeon-scientist.