Mediator Subunit Med4 Enforces Metastatic Dormancy in Breast Cancer
Seong-Yeon Bae1,2,3,4, Hsiang-Hsi Ling1,2,3,4, Yi Chen2,5,6
1Cancer Metastasis Initiative, Herbert Irving Comprehensive Cancer Center, Columbia University Irving Medical Center, New York, New York 10032, USA.
Abstract:
Long term survival of breast cancer patients is limited due to recurrence from metastatic dormant cancer cells. However, the mechanisms by which these dormant breast cancer cells survive and awaken remain poorly understood. Our unbiased genome-scale genetic screen in mice identified Med4 as a novel cancer-cell intrinsic gatekeeper in metastatic reactivation. MED4 haploinsufficiency is prevalent in metastatic breast cancer patients and correlates with poorer prognosis. Syngeneic xenograft models revealed that Med4 enforces breast cancer dormancy. Contrary to the canonical function of the Mediator complex in activating gene expression, Med4 maintains 3D chromatin compaction and enhancer landscape, by preventing enhancer priming or activation through the suppression of H3K4me1 deposition. Med4 haploinsufficiency disrupts enhancer poise and reprograms the enhancer dynamics to facilitate extracellular matrix (ECM) gene expression and integrin-mediated mechano-transduction, driving metastatic growth. Our findings establish Med4 as a key regulator of cellular dormancy and a potential biomarker for high-risk metastatic relapse.
Insights
Med4 protein acts as a gatekeeper for dormant breast cancer cells, preventing their reactivation and metastatic growth. Its deficiency is linked to poorer patient prognosis, highlighting Med4 as a potential biomarker for high-risk relapse.
Area of Science:
- Cancer Biology
- Molecular Oncology
- Epigenetics
Background:
- Long-term survival in breast cancer patients is often compromised by recurrence from metastatic dormant cancer cells.
- The precise mechanisms governing the survival and reactivation of these dormant cells are not well understood.
Purpose of the Study:
- To identify novel regulators of metastatic reactivation in breast cancer.
- To elucidate the role of Med4 in maintaining cancer cell dormancy and metastatic potential.
Main Methods:
- Genome-scale genetic screen in mice to identify genes involved in metastatic reactivation.
- Syngeneic xenograft models to study the function of Med4 in breast cancer dormancy.
- Chromatin immunoprecipitation and gene expression analysis to investigate Med4's regulatory mechanisms.
Main Results:
- Med4 was identified as a critical gatekeeper suppressing metastatic reactivation.
- Med4 haploinsufficiency, prevalent in metastatic breast cancer patients, correlates with poorer prognosis.
- Med4 maintains 3D chromatin compaction and suppresses enhancer priming by inhibiting H3K4me1 deposition, thereby enforcing dormancy.
- Med4 deficiency disrupts enhancer dynamics, promoting extracellular matrix gene expression and driving metastatic growth.
Conclusions:
- Med4 is a key regulator of cellular dormancy in breast cancer.
- Med4 functions uniquely within the Mediator complex to maintain chromatin structure and prevent metastatic reactivation.
- Med4 serves as a potential biomarker for predicting high-risk metastatic relapse in breast cancer patients.
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