SUMMARY HER2 is considered as a driver oncogene responsible for the HER2+ subtype of breast cancer. However, it is still unclear how HER2 induces the oncogenic transformation of breast cancer stem cells (BCSCs) and initiates tumorigenesis during premalignant stage breast cancer. Here, we used clinical samples and mouse models of HER2+ breast cancer to demonstrate that neither BCSCs nor their cell-of-origin express HER2/Neu in early-stage breast tumors. Instead, our results demonstrate that Neu overexpression results in the transformation of BCSCs in a non-cell-autonomous manner via triggering DNA damage and somatic mutagenesis in their Neu-negative cell-of-origin. This is caused by the increased oxidative stress in the tissue microenvironment generated by altered energy metabolism and increased reactive oxygen species levels in Neu-overexpressing mammary ducts. Therefore, our findings illustrate a previously unrecognized mechanism of HER2-induced breast tumor initiation in vivo with potential impacts on future preventive treatments for HER2+ premalignant breast cancer.

SETD2 is a tumor suppressor that is frequently inactivated in several cancer types. The mechanisms through which SETD2 inactivation promotes cancer are unclear, and whether targetable vulnerabilities exist in these tumors is unknown. Here we identify heightened mTORC1-associated gene expression programs and functionally higher levels of oxidative metabolism and protein synthesis as prominent consequences of Setd2 inactivation in KRAS-driven mouse models of lung adenocarcinoma. Blocking oxidative respiration and mTORC1 signaling abrogates the high rates of tumor cell proliferation and tumor growth specifically in SETD2-deficient tumors. Our data nominate SETD2 deficiency as a functional marker of sensitivity to clinically actionable therapeutics targeting oxidative respiration and mTORC1 signaling.
© 2023. The Author(s).

Preeclampsia (PE) is a common syndrome of pregnancy, characterized by new-onset hypertension and proteinuria after gestational week 20, or new onset of hypertension and significant end-organ dysfunction. In the worst cases, it can threaten the survival of both mother and baby. Extracellular vesicles (EVs) are lipid-bilayer nanoparticles released from cells. They are involved in cell-cell communication and transport of diverse cargo molecules. Small extracellular vesicles (sEVs, exosomes) are defined by their size and biogenesis within the endocytic compartment of the cell or reverse budding of the plasma membrane. The function of circulating gestational EVs, released from maternal organs or the placenta, remains to be explored. Here, we focused on sEVs that circulate in the maternal blood in the third trimester of human pregnancy and hypothesized that sEVs from pregnant women with PE play a role in regulation of vessel tone. When compared to sEVs from women with uncomplicated pregnancies, ex vivo exposure of isolated mouse mesenteric arteries to sEVs purified from the plasma of pregnant women with PE led to constriction in response to intraluminal pressure. This effect was not observed using microvesicles from the plasma of women with PE or using PE plasma that was depleted of EVs. Blood vessels exposed to sEVs from women with PE were also more resistant to methacholine-stimulated relaxation. Immunofluorescence microscopy confirmed the presence of sEVs within the vessel wall. Together, these data support the notion that circulating sEVs from pregnant women play a role in the regulation of arterial tone.
Copyright © 2022 International Society for the Study of Hypertension in Pregnancy. Published by Elsevier B.V. All rights reserved.

Gpr125 is an orphan G-protein coupled receptor, with homology to cell adhesion and axonal guidance factors, that is implicated in planar polarity and control of cell movements. By lineage tracing we demonstrate that Gpr125 is a highly specific marker of bipotent mammary stem cells in the embryo and of multiple long-lived unipotent basal mammary progenitors in perinatal and postnatal glands. Nipple-proximal Gpr125+ cells express a transcriptomic profile indicative of chemo-repulsion and cell movement, whereas Gpr125+ cells concentrated at invasive ductal tips display a hybrid epithelial-mesenchymal phenotype and are equipped to bind chemokine and growth factors and secrete a promigratory matrix. Gpr125 progenitors acquire bipotency in the context of transplantation and cancer and are greatly expanded and massed at the pushing margins of short latency MMTV-Wnt1 tumors. High Gpr125 expression identifies patients with particularly poor outcome within the basal breast cancer subtype highlighting its potential utility as a factor to stratify risk.
© 2022. The Author(s).

While initiation is established as a critical step in tumorigenesis, the identity of the cell of origin for lung adenocarcinoma and the mechanism controlling susceptibility to initiation remain elusive. Here we show that lung tumor suppressor Gprc5a-knockout (KO) mice are susceptible to initiation of lung tumorigenesis. Bronchioalveolar stem cells (BASC) and alveolar type 2 (AT2) cells were aberrantly expanded in Gprc5a-KO mouse lungs compared with those in wild-type (WT) mice, suggesting that Gprc5a-KO might confer susceptibility to initiation by increasing the cell of origin in mouse lungs. BASCs from Gprc5a-KO mice (KO-BASC) exhibited significantly increased stemness and self-renewal potential and reduced differentiation capacity compared with BASCs from WT mice (WT-BASC). AT2 cells did not possess self-renewal potential regardless of Gprc5a status. KO-BASCs expressed a stem-like gene profile with upregulated Abcg2, EGFR, and NF-κB signaling compared with WT-BASCs. Blockade of EGFR and NF-κB signaling inhibited both expansion of BASC and AT2 cells and lung tumorigenesis. Abcg2 was expressed in active KO-BASCs as well as in lung tumor cells but not in quiescent WT-BASCs or AT2 cells, supporting that lung adenocarcinoma cells are derived from Abcg2-positive KO-BASCs (active). Taken together, Gprc5a deletion leads to expansion of active BASCs via dysregulated EGFR and NF-κB signaling that confers susceptibility to initiation of lung tumorigenesis, marking Abcg2-positive BASCs as candidate cell of origin for lung adenocarcinoma.
Identification of active bronchioalveolar stem cells as lung adenocarcinoma cells of origin provides insights into mechanisms of lung tumorigenesis and could facilitate development of effective strategies for cancer prevention and therapy. See related commentary by Osborne and Minna, p. 972.
©2022 American Association for Cancer Research.