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Esther Rheinbay, PhDMember of the Faculty of MedicineMassachusetts General Hospital Cancer CenterHarvard Medical School
Most known genomic drivers of cancer are in coding genes, affecting the encoded protein’s interaction with other proteins, DNA or biological compounds. Recent advances in DNA sequencing technology have made it possible to study non-coding regions that regulate these protein-coding genes. Several cancer drivers have been identified and characterized in these regulatory regions, however, this genomic territory remains relatively unexplored in human tumors. The Rheinbay laboratory concentrates on identifying and functionally characterizing these non-coding drivers in the sequences of tumor whole genomes through development of novel analysis strategies and collaborations with experimental investigators.
We are also interested in tumors, especially breast cancers, for which no known protein-coding driver alterations have been found. In the age of targeted therapy, these tumors pose a special challenge in that they leave few treatment options for patients beyond conventional chemotherapy. We believe that finding novel genomic and epigenomic, protein-coding and regulatory therapeutic targets in these tumors will have significant clinical implications.
Regulatory driver mutations in cancer genomes
Genomic cancer driver discovery has traditionally focused on protein-coding genes (the human exome), and large-scale sequencing of these genes in thousands of tumors has led to the discovery of novel frequently altered genes. However, exome sequencing focused only on coding genes does not allow analysis of non-coding regions in the human genome. Protein-coding genes are regulated by several types of genomic elements that control their expression (promoters, distal enhancers and boundary elements), translation (5’UTRs) and mRNA stability (3’UTRs). Alterations in the DNA sequence of these elements thus directly affect the expression and regulation of the target gene. Several such non-coding elements have been identified as recurrently altered in human cancer, and functionally characterized, although these non-coding drivers appear infrequent compared to protein-coding oncogenes and tumor suppressors. One reason might be that gene regulation is highly tissue-specific, and therefore driver alterations in non-coding regions might create a fitness advantage in only a single tumor type. Finding such a specific driver requires a suficient number of whole genomes from this tumor type. With recent advances in DNA sequencing technology and an increasing number of whole cancer genomes available for analysis, we are just starting to map out and characterize regulatory driver alterations. The Rheinbay laboratory works on the development of novel methods to identify non-coding driver candidates using genomic and epigenomic sources of information, and to understand their impact on tumor initiation, progression and treatment resistance through collaborations with experimental colleagues.
We have recently identified a recurrent mutation in the promoter of the breast cancer oncogene FOXA1. This mutation increases expression through augmenting a binding site for E2F, leading to E2F protein recruitment. In addition, FOXA1 overexpression leads to resistance to the breast cancer drug,fulvestrant. We are now investigating the implications and mechanism of action of this mutation in breast cancer progression and treatment resistance.
Hotspot mutation in the FOXA1 promoter in breast cancer and proposed mechanism of action
Finding targetable vulnerabilities in cancers without known drivers
From recent large genome and exome sequencing studies of different cancer types, it has become apparent that there are almost always patients whose tumors harbor no common driver alteration such as BRAFmutation in melanoma, HER2 amplification, or hormone receptor expression in breast and prostate cancer. In an era of treatments targeting such alterations specific to a patient’s cancer cells, a lack of potentially druggable cancer drivers severely limits the repertoire of available therapy options. Rather than being truly without any drivers, these tumors are likely driven by yet uncharacterized protein-coding or regulatory genomic alterations, or an oncogenic state induced and maintained by epigenetic changes. Our research is focused on finding the drivers and vulnerabilities of these particular tumors by integrating genomics and epigenomics data, with the ultimate goal of connecting patients to effective targeted treatments.
Rheinbay E, Parasuraman P, Grimsby J, et al. Recurrent and functional regulatory mutations in breast cancer. Nature. 2017;547:55-60.
Suva ML*, Rheinbay E*, Gillespie SM, et al. Reconstructing and reprogramming the tumor-propagating potential of glioblastoma stem-like cells. Cell. 2014;157:580-94.
Rheinbay E*, Suva ML*, Gillespie SM, et al. An aberrant transcription factor network essential for Wnt signaling and stem cell maintenance in glioblastoma. Cell Reports. 2013;3:1567-79.
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