Search

Stem cells in many tissues sustain themselves by entering a quiescent state to avoid genomic insults and to prevent exhaustion caused by excessive proliferation. In the mammary gland, the identity and characteristics of quiescent epithelial stem cells are not clear. Here, we identify a quiescent mammary epithelial cell population expressing high levels of Bcl11b and located at the interface between luminal and basal cells. Bcl11bhigh cells are enriched for cells that can regenerate mammary glands in secondary transplants. Loss of Bcl11b leads to a Cdkn2a-dependent exhaustion of ductal epithelium and loss of epithelial cell regenerative capacity. Gain- and loss-of-function studies show that Bcl11b induces cells to enter the G0 phase of the cell cycle and become quiescent. Taken together, these results suggest that Bcl11b acts as a central intrinsic regulator of mammary epithelial stem cell quiescence and exhaustion and is necessary for long-term maintenance of the mammary gland.

Cancer incidence escalates exponentially with advancing age; however, the underlying mechanism remains unclear. In this study, we build a chronological molecular clock at single-cell transcription level with a mammary stem cell-enriched population to depict physiological aging dynamics in female mice. We find that the mammary aging process is asynchronous and progressive, initiated by an early senescence program, succeeded by an entropic late senescence program with elevated cancer associated pathways, vulnerable to cancer predisposition. The transition towards senescence program is governed by a stem cell factor Bcl11b, loss of which accelerates mammary ageing with enhanced DMBA-induced tumor formation. We have identified a drug TPCA-1 that can rejuvenate mammary cells and significantly reduce aging-related cancer incidence. Our findings establish a molecular portrait of progressive mammary cell aging and elucidate the transcriptional regulatory network bridging mammary aging and cancer predisposition, which has potential implications for the management of cancer prevalence in the aged. Aging-related cancer incidence remains not fully understood. Here, the authors depict a progressive process of senescence in murine mammary stem cells at single-cell resolution, which is governed by the transcription factor Bcl11b and associated with enhanced chemical-induced tumorigenesis in aged mice. [ABSTRACT FROM AUTHOR]

As precision medicine increases the response rate of treatment, tumors frequently bypass inhibition, and reoccur. In order for treatment to be effective long term, the mechanisms enabling treatment adaptation need to be understood. Here, we report a mouse model that, in the absence of p53 and the presence of oncogenic KrasG12D, develops breast tumors. Upon inactivation of KrasG12D, tumors initially regress and enter remission. Subsequently, the majority of tumors adapt to the withdrawal of KrasG12D expression and return. KrasG12D-independent tumor cells show a strong mesenchymal profile with active RAS-RAF-MEK-ERK (MAPK/ERK) signaling. Both KrasG12D-dependent and KrasG12D-independent tumors display a high level of genomic instability, and KrasG12D-independent tumors harbor numerous amplified genes that can activate the MAPK/ERK signaling pathway. Our study identifies both epithelial-mesenchymal transition (EMT) and active MAPK/ERK signaling in tumors that adapt to oncogenic KrasG12D withdrawal in a novel Trp53 -/- breast cancer mouse model. To achieve long-lasting responses in the clinic to RAS-fueled cancer, treatment will need to focus in parallel on obstructing tumors from adapting to oncogene inhibition. [ABSTRACT FROM AUTHOR]

Previous studies have proposed that epithelial to mesenchymal transition (EMT) in breast cancer cells regulates metastasis, stem cell properties and chemo-resistance; most studies were based on in vitro culture of cell lines and mouse transgenic cancer models. However, the identity and function of cells expressing EMT-associated genes in normal murine mammary gland homeostasis and human breast cancer still remains under debate. Using in vivo lineage tracing and triple negative breast cancer (TNBC) patient derived xenografts we demonstrate that the repopulating capacity in normal mammary epithelial cells and tumorigenic capacity in TNBC is independent of expression of EMT-associated genes. In breast cancer, while a subset of cells with epithelial and mesenchymal phenotypes have stem cell activity, in many cells that have lost epithelial characteristics with increased expression of mesenchymal genes, have decreased tumor-initiating capacity and plasticity. These findings have implications for the development of effective therapeutic agents targeting tumor-initiating cells. [ABSTRACT FROM AUTHOR]

The article discusses a 2022 study on a minority population of LMO2+ breast cancer cells that integrate into the vasculature and initiate metastasis. Topics covered include the reduction of lung metastasis by LMO2 knockdown in human breast tumors, and the binding of LMO2 to STAT3 that is required for the latter's activation. Also noted is the identification of cells with angiogenic features that establishes the LMO2-STAT3 signaling axis as a therapeutic target in breast cancer metastasis.

A correction is presented to the article "Stimulation of natural killer cells with a CD137-specific antibody enhances trastuzumab efficacy in xenotransplant models of breast cancer" which appeared in the previous issue of the periodical.