Starvation and antimetabolic therapy promote cytokine release and recruitment of immune cells.

Cellular starvation is typically a consequence of tissue injury that disrupts the local blood supply but can also occur where cell populations outgrow the local vasculature, as observed in solid tumors. Cells react to nutrient deprivation by adapting their metabolism, or, if starvation is prolonged, it can result in cell death. Cell starvation also triggers adaptive responses, like angiogenesis, that promote tissue reorganization and repair, but other adaptive responses and their mediators are still poorly characterized. To explore this issue, we analyzed secretomes from glucose-deprived cells, which revealed up-regulation of multiple cytokines and chemokines, including IL-6 and IL-8, in response to starvation stress. Starvation-induced cytokines were cell type-dependent, and they were also released from primary epithelial cells. Most cytokines were up-regulated in a manner dependent on NF-κB and the transcription factor of the integrated stress response ATF4, which bound directly to the IL-8 promoter. Furthermore, glutamine deprivation, as well as the antimetabolic drugs 2-deoxyglucose and metformin, also promoted the release of IL-6 and IL-8. Finally, some of the factors released from starved cells induced chemotaxis of B cells, macrophages, and neutrophils, suggesting that nutrient deprivation in the tumor environment can serve as an initiator of tumor inflammation.

Luminal Rank loss decreases cell fitness leading to basal cell bipotency in parous mammary glands.

Rank signaling pathway regulates mammary gland homeostasis and epithelial cell differentiation. Although Rank receptor is expressed by basal cells and luminal progenitors, its role in each individual cell lineage remains unclear. By combining temporal/lineage specific Rank genetic deletion with lineage tracing techniques, we found that loss of luminal Rank reduces the luminal progenitor pool and leads to aberrant alveolar-like differentiation with high protein translation capacity in virgin mammary glands. These Rank-deleted luminal cells are unable to expand during the first pregnancy, leading to lactation failure and impairment of protein synthesis potential in the parous stage. The unfit parous Rank-deleted luminal cells in the alveoli are progressively replaced by Rank-proficient cells early during the second pregnancy, thereby restoring lactation. Transcriptomic analysis and functional assays point to the awakening of basal bipotency after pregnancy by the induction of Rank/NF-κB signaling in basal parous cell to restore lactation and tissue homeostasis.

RANK links senescence to stemness in the mammary epithelia, delaying tumor onset but increasing tumor aggressiveness.

Rank signaling enhances stemness in mouse and human mammary epithelial cells (MECs) and mediates mammary tumor initiation. Mammary tumors initiated by oncogenes or carcinogen exposure display high levels of Rank and Rank pathway inhibitors have emerged as a new strategy for breast cancer prevention and treatment. Here, we show that ectopic Rank expression in the mammary epithelia unexpectedly delays tumor onset and reduces tumor incidence in the oncogene-driven Neu and PyMT models. Mechanistically, we have found that ectopic expression of Rank or exposure to Rankl induces senescence, even in the absence of other oncogenic mutations. Rank leads to DNA damage and senescence through p16/p19. Moreover, RANK-induced senescence is essential for Rank-driven stemness, and although initially translates into delayed tumor growth, eventually promotes tumor progression and metastasis. We uncover a dual role for Rank in the mammary epithelia: Rank induces senescence and stemness, delaying tumor initiation but increasing tumor aggressiveness.