Identification of Functional Networks of Estrogen- and c-Myc-Responsive Genes and Their Relationship to Response to Tamoxifen Therapy in Breast Cancer

Abstract

BackgroundEstrogen is a pivotal regulator of cell proliferation in the normal breast and breast cancer. Endocrine therapies targeting the estrogen receptor are effective in breast cancer, but their success is limited by intrinsic and acquired resistance.Methodology/Principal FindingsWith the goal of gaining mechanistic insights into estrogen action and endocrine resistance, we classified estrogen-regulated genes by function, and determined the relationship between functionally-related genesets and the response to tamoxifen in breast cancer patients. Estrogen-responsive genes were identified by transcript profiling of MCF-7 breast cancer cells. Pathway analysis based on functional annotation of these estrogen-regulated genes identified gene signatures with known or predicted roles in cell cycle control, cell growth (i.e. ribosome biogenesis and protein synthesis), cell death/survival signaling and transcriptional regulation. Since inducible expression of c-Myc in antiestrogen-arrested cells can recapitulate many of the effects of estrogen on molecular endpoints related to cell cycle progression, the estrogen-regulated genes that were also targets of c-Myc were identified using cells inducibly expressing c-Myc. Selected genes classified as estrogen and c-Myc targets displayed similar levels of regulation by estrogen and c-Myc and were not estrogen-regulated in the presence of siMyc. Genes regulated by c-Myc accounted for 50% of all acutely estrogen-regulated genes but comprised 85% (110/129 genes) in the cell growth signature. siRNA-mediated inhibition of c-Myc induction impaired estrogen regulation of ribosome biogenesis and protein synthesis, consistent with the prediction that estrogen regulates cell growth principally via c-Myc. The ‘cell cycle’, ‘cell growth’ and ‘cell death’ gene signatures each identified patients with an attenuated response in a cohort of 246 tamoxifen-treated patients. In multivariate analysis the cell death signature was predictive independent of the cell cycle and cell growth signatures.Conclusions/SignificanceThese functionally-based gene signatures can stratify patients treated with tamoxifen into groups with differing outcome, and potentially identify distinct mechanisms of tamoxifen resistance.

MUC1-induced alterations in a lipid metabolic gene network predict response of human breast cancers to tamoxifen treatment

“…Predictive analysis of gene expression has been used to identify signatures that are predictive of recurrence in patients with primary breast tumors treated with tamoxifen (10,(24)(25)(26). The findings of a 2-gene signature by Ma et al (10) have been questioned (27)(28)(29).…”

HSPC111 Governs Breast Cancer Growth by Regulating Ribosomal Biogenesis

“…Immunoprecipitated proteins were eluted with 4Â SDS-PAGE sample buffer by boiling for 5 minutes, and then assessed by Western blot analysis. The proteins within the purified immunoprecipitates were also identified by MALDI-TOF MS (Bruker Daltonics) following the standard procedures (26,27).…”

“…RTCD1 was previously identified in the HeLa cell extract, and it is an enzyme that catalyzes conversion of a 3 0 -phosphate group into the 2 0 ,3 0 -cyclic phosphodiester at the 3 0 end of RNAs (also named RNA 2,3-cyclic phosphate) in an ATP-dependent manner (23,24). RNA 2,3-cyclic phosphate ends are crucially important in ribosome assembly through regulating RNA-protein binding and RNA stability (27,(29)(30)(31). Previous studies have validated that RTCD1-mediated conversion of 2,3-cyclic phosphate ends on rRNAs is indispensable to 18S rRNA biogenesis (32,33).…”

The Proto-Oncogene Myc Is Essential for Mammary Stem Cell Function

“…Myc expression is often deregulated in breast cancer, in particular, in the triplenegative subtype [7,8]. Moreover, Myc is an estrogen receptor-a (ERa) target, and there is a significant overlap between ERa-and Myc-regulated genes associated with the control of proliferation [9].…”