Estrogen receptor alpha (ER?/ESR1) mediates the p53-independent overexpression of MDM4/MDMX and MDM2 in human breast cancer.

ABSTRACT: MDM2 and MDM4 are heterodimeric, non-redundant oncoproteins that potently inhibit the p53 tumor suppressor protein. MDM2 and MDM4 also enhance the tumorigenicity of breast cancer cells in in vitro and in vivo models and are overexpressed in primary human breast cancers. Prior studies have characterized Estrogen Receptor Alpha (ER?/ESR1) as a regulator of MDM2 expression and an MDM2- and p53-interacting protein. However, similar crosstalk between ER? and MDM4 has not been investigated. Moreover, signaling pathways that mediate the overexpression of MDM4 in human breast cancer remain to be elucidated. Using the Cancer Genome Atlas (TCGA) breast invasive carcinoma patient cohort, we have analyzed correlations between ER? status and MDM4 and MDM2 expression in primary, treatment-naïve, invasive breast carcinoma samples. We report that the expression of MDM4 and MDM2 is elevated in primary human breast cancers of luminal A/B subtypes and associates with ER?-positive disease, independently of p53 mutation status. Furthermore, in cell culture models, ER? positively regulates MDM4 and MDM2 expression via p53-independent mechanisms, and these effects can be blocked by the clinically-relevant endocrine therapies fulvestrant and tamoxifen. Additionally, ER? also positively regulates p53 expression. Lastly, we report that endogenous MDM4 negatively regulates ER? expression and forms a protein complex with ER? in breast cancer cell lines and primary human breast tumor tissue. This suggests direct signaling crosstalk and negative feedback loops between ER? and MDM4 expression in breast cancer cells. Collectively, these novel findings implicate ER? as a central component of the p53-MDM2-MDM4 signaling axis in human breast cancer.

SUBMITTER: Swetzig WM 

PROVIDER: S-EPMC4941297 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature