ABSTRACT
The majority of women diagnosed with lymph node-negative breast cancer are unnecessarily treated with damaging chemotherapeutics after surgical resection. This highlights the importance of understanding and more accurately predicting patient prognosis. In the present study, we define the transcriptional networks regulating well-established prognostic gene expression signatures. We find that the same set of transcriptional regulators consistently lie upstream of both 'prognosis' and 'proliferation' gene signatures, suggesting that a central transcriptional network underpins a shared phenotype within these signatures. Strikingly, the master transcriptional regulators within this network predict recurrence risk for lymph node-negative breast cancer better than currently used multigene prognostic assays, particularly in estrogen receptor-positive patients. Simultaneous examination of p16(INK4A) expression, which predicts tumours that have bypassed cellular senescence, revealed that intermediate levels of p16(INK4A) correlate with an intact pRB pathway and improved survival. A combination of these master transcriptional regulators and p16(INK4A), termed the OncoMasTR score, stratifies tumours based on their proliferative and senescence capacity, facilitating a clearer delineation of lymph node-negative breast cancer patients at high risk of recurrence, and thus requiring chemotherapy. Furthermore, OncoMasTR accurately classifies over 60% of patients as 'low risk', an improvement on existing prognostic assays, which has the potential to reduce overtreatment in early-stage patients. Taken together, the present study provides new insights into the transcriptional regulation of cellular proliferation in breast cancer and provides an opportunity to enhance and streamline methods of predicting breast cancer prognosis.
Subject(s)
Breast Neoplasms/genetics , Gene Regulatory Networks , Adult , Aged , Aged, 80 and over , Animals , Breast Neoplasms/metabolism , Breast Neoplasms/therapy , Cell Proliferation/genetics , Cells, Cultured , Cellular Senescence/genetics , Cohort Studies , Female , Genes, p16 , Humans , Lymphatic Metastasis/genetics , Mammary Glands, Human/cytology , Mammary Glands, Human/metabolism , Mice , Middle Aged , Prognosis , Promoter Regions, Genetic , RNA, Messenger/genetics , RNA, Messenger/metabolism , RNA, Neoplasm/genetics , RNA, Neoplasm/metabolism , Receptors, Estrogen/metabolism , Risk Factors , Tissue Array AnalysisABSTRACT
Polycomb group proteins are repressive chromatin modifiers with essential roles in metazoan development, cellular differentiation and cell fate maintenance. How Polycomb proteins access active chromatin to confer transcriptional silencing during lineage transitions remains unclear. Here we show that the Polycomb repressive complex 2 (PRC2) component PHF19 binds trimethylated histone H3 Lys36 (H3K36me3), a mark of active chromatin, via its Tudor domain. PHF19 associates with the H3K36me3 demethylase NO66, and it is required to recruit the PRC2 complex and NO66 to stem cell genes during differentiation, leading to PRC2-mediated trimethylation of histone H3 Lys27 (H3K27), loss of H3K36me3 and transcriptional silencing. We propose a model whereby PHF19 functions during mouse embryonic stem cell differentiation to transiently bind the H3K36me3 mark via its Tudor domain, forming essential contact points that allow recruitment of PRC2 and H3K36me3 demethylase activity to active gene loci during their transition to a Polycomb-repressed state.
