Tissues contain distinct stem cell niches, but whether cell turnover is coordinated between niches during growth is unknown. Here, we report that in mouse skin, hair growth is accompanied by sebaceous gland and interfollicular epidermis expansion. During hair growth, cells in the bulge and outer root sheath temporarily upregulate the glutamate transporter SLC1A3, and the number of SLC1A3 basal cells in interfollicular epidermis and sebaceous gland increases. Fate mapping of SLC1A3 cells in mice revealed transient expression in proliferating stem/progenitor cells in all three niches. Deletion of delays hair follicle anagen entry, uncouples interfollicular epidermis and sebaceous gland expansion from the hair cycle, and leads to reduced fur density in aged mice, indicating a role of SLC1A3 in stem/progenitor cell activation. Modulation of metabotropic glutamate receptor 5 activity mimics the effects of SLC1A3 deletion or inhibition. These data reveal that stem/progenitor cell activation is synchronized over distinct niches during growth and identify SLC1A3 as a general marker and effector of activated epithelial stem/progenitor cells throughout the skin.

EphB receptors regulate the proliferation and positioning of intestinal stem and progenitor cells. In addition, they can act as tumor promoters for adenoma development but suppress progression to invasive carcinoma. We used imatinib to abrogate Abl kinase activity in Apc(Min/+) mice and in mice with LGR5(+) stem cells that were genetically engineered to develop adenomatous polyposis coli. Imatinib treatment inhibited the tumor-promoting effects of EphB signaling without attenuating EphB-mediated tumor suppression, demonstrating a role for EphB signaling in the initiation of intestinal tumors. The imatinib treatment regimen extended the life span of Apc(Min/+) mice and reduced cell proliferation in cultured slices of adenomas from patients with familial adenomatous polyposis. These findings connect the EphB signaling pathway to the regulation of intestinal adenoma initiation via Abl kinase. Our findings may have clinical implications for pharmacological therapy against adenoma formation and cancer progression in patients predisposed to develop colorectal cancer.

Prostate cancer is a heterogeneous disease with a need for new prognostic biomarkers. Human leukocyte antigen (HLA) genes are highly polymorphic genes central to antigen presentation to T‐cells. Two alleles, HLA‐A*02:01 and HLA‐A*24:02, have been associated with prognosis in patients diagnosed with de novo metastatic prostate cancer. We leveraged the next‐generation sequenced cohorts CPC‐GENE and TCGA‐PRAD to examine HLA alleles, antiviral T‐cell receptors and prostate cancer disease recurrence after prostatectomy. Carrying HLA‐A*02:01 (111/229; 48% of patients) was independently associated with disease recurrence in patients with low‐intermediate risk prostate cancer. HLA‐A*11 (carried by 42/441; 10% of patients) was independently associated with rapid disease recurrence in patients with high‐risk prostate cancer. Moreover, HLA‐A*02:01 carriers in which anti‐cytomegalovirus T‐cell receptors (CMV‐TCR) were identified in tumors (13/144; 10% of all patients in the cohort) had a higher risk of disease recurrence than CMV‐TCR‐negative patients. These findings suggest that HLA‐type and CMV immunity may be valuable biomarkers for prostate cancer progression.

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