Methyl-CpG binding domain protein 2 plays a causal role in breast cancer growth and metastasis

Methyl-CpG-binding domain protein 2 (Mbd2), a reader of DNA-methylation, has been implicated in the progression of several types of malignancies, including breast cancer. To test whether Mbd2, which is overexpressed in human breast cancer samples and in MMTV-PyMT mammary pads, plays a causal role in mammary tumor growth and metastasis we depleted Mbd2 in transgenic MMTV-PyMT model of breast cancer by cross-breeding with Mbd2 knockout mice to generate heterozygous (PyMT;Mbd2+/-) and homozygous (PyMT;Mbd2-/-) animals. We found that Mbd2 depletion caused a gene dose-dependent delay in mammary tumor formation, reduced primary tumor burden, and lung metastasis at the experimental endpoint. In addition, animals from the PyMT;Mbd2-/- group survived significantly longer compared to the wildtype (PyMT;Mbd2+/+) and PyMT;Mbd2+/- arms. Transcriptomic and proteomic analyses of the primary tumors obtained from PyMT;Mbd2+/+ and PyMT;Mbd2+/- groups revealed that Mbd2 depletion alters several key determinants of the molecular signaling networks related to tumorigenesis and metastasis, which thereby demonstrate that Mbd2 is regulating transcriptional programs critical for breast cancer. To our knowledge, this is the first study demonstrating a causal role for a DNA-methylation reader in breast cancer. Results from this study will provide the rationale for further development of first-in-class targeted epigenetic therapies against Mbd2 to inhibit the progression of breast and other common cancers.