Epigenetic reprogramming of lineage-committed human mammary epithelial cells requires DNMT3A and loss of DOT1L

Summary Organogenesis and tissue development occur through sequential stepwise processes leading to increased lineage restriction and loss of pluripotency. An exception to this appears in the adult human breast, where rare variant epithelial cells exhibit pluripotency and multilineage differentiation potential when removed from the signals of their native microenvironment. This phenomenon provides a unique opportunity to study mechanisms that lead to cellular reprogramming and lineage plasticity in real time. Here, we show that primary human mammary epithelial cells (HMECs) lose expression of differentiated mammary epithelial markers in a manner dependent on paracrine factors and epigenetic regulation. Furthermore, we demonstrate that HMEC reprogramming is dependent on gene silencing by the DNA methyltransferase DNMT3A and loss of histone transcriptional marks following downregulation of the methyltransferase DOT1L. These results demonstrate that lineage commitment in adult tissues is context dependent and highlight the plasticity of somatic cells when removed from their native tissue microenvironment.
Graphical Abstract
Highlights • vHMECs arise through epigenetic modification of pre-existing human breast cells • DNA methylation by DNMT3a is required for vHMEC formation • Loss of DOT1L and active histone methylation marks accelerates vHMEC formation • Loss of mammary identity requires changes in both DNA and histone methylation
In this article, Kuperwasser and colleagues show that, upon removal from their native microenvironment, rare pre-existing human mammary epithelial cells undergo stochastic epigenetic reprogramming and lose mammary lineage identity. This dedifferentiation occurs through addition of repressive promoter methylation marks by DNMT3a and removal of active histone methylation marks through DOT1L loss, which together suppress mammary lineage commitment gene expression.