Dietary interventions as regulators of stem cell behavior in homeostasis and disease.

Stem cells maintain tissues by balancing self-renewal with differentiation. A stem cell's local microenvironment, or niche, informs stem cell behavior and receives inputs at multiple levels. Increasingly, it is becoming clear that the overall metabolic status of an organism or metabolites themselves can function as integral members of the niche to alter stem cell fate. Macroscopic dietary interventions such as caloric restriction, the ketogenic diet, and a high-fat diet systemically alter an organism's metabolic state in different ways. Intriguingly, however, they all converge on a propensity to enhance self-renewal. Here, we highlight our current knowledge on how dietary changes feed into stem cell behavior across a wide variety of tissues and illuminate possible explanations for why diverse interventions can result in similar stem cell phenotypes. In so doing, we hope to inspire new avenues of inquiry into the importance of metabolism in stem cell homeostasis and disease.

The KDM5A/RBP2 histone demethylase represses NOTCH signaling to sustain neuroendocrine differentiation and promote small cell lung cancer tumorigenesis.

More than 90% of small cell lung cancers (SCLCs) harbor loss-of-function mutations in the tumor suppressor gene RB1 The canonical function of the RB1 gene product, pRB, is to repress the E2F transcription factor family, but pRB also functions to regulate cellular differentiation in part through its binding to the histone demethylase KDM5A (also known as RBP2 or JARID1A). We show that KDM5A promotes SCLC proliferation and SCLC's neuroendocrine differentiation phenotype in part by sustaining expression of the neuroendocrine transcription factor ASCL1. Mechanistically, we found that KDM5A sustains ASCL1 levels and neuroendocrine differentiation by repressing NOTCH2 and NOTCH target genes. To test the role of KDM5A in SCLC tumorigenesis in vivo, we developed a CRISPR/Cas9-based mouse model of SCLC by delivering an adenovirus (or an adeno-associated virus [AAV]) that expresses Cre recombinase and sgRNAs targeting Rb1, Tp53, and Rbl2 into the lungs of Lox-Stop-Lox Cas9 mice. Coinclusion of a KDM5A sgRNA decreased SCLC tumorigenesis and metastasis, and the SCLCs that formed despite the absence of KDM5A had higher NOTCH activity compared to KDM5A+/+ SCLCs. This work establishes a role for KDM5A in SCLC tumorigenesis and suggests that KDM5 inhibitors should be explored as treatments for SCLC.

Autochthonous tumors driven by Rb1 loss have an ongoing requirement for the RBP2 histone demethylase.

Inactivation of the retinoblastoma gene (RB1) product, pRB, is common in many human cancers. Targeting downstream effectors of pRB that are central to tumorigenesis is a promising strategy to block the growth of tumors harboring loss-of-function RB1 mutations. One such effector is retinoblastoma-binding protein 2 (RBP2, also called JARID1A or KDM5A), which encodes an H3K4 demethylase. Binding of pRB to RBP2 has been linked to the ability of pRB to promote senescence and differentiation. Importantly, genetic ablation of RBP2 is sufficient to phenocopy pRB's ability to induce these cellular changes in cell culture experiments. Moreover, germline Rbp2 deletion significantly impedes tumorigenesis in Rb1+/- mice. The value of RBP2 as a therapeutic target in cancer, however, hinges on whether loss of RBP2 could block the growth of established tumors as opposed to simply delaying their onset. Here we show that conditional, systemic ablation of RBP2 in tumor-bearing Rb1+/- mice is sufficient to slow tumor growth and significantly extend survival without causing obvious toxicity to the host. These findings show that established Rb1-null tumors require RBP2 for growth and further credential RBP2 as a therapeutic target in human cancers driven by RB1 inactivation.

A Medical Student-Run Telehealth Primary Care Clinic During the COVID-19 Pandemic: Maintaining Care for the Underserved.

BACKGROUND: In this report, we outline our approach to implementing a hybrid in-person and virtual clinic model at a student-run free clinic (SRFC) during the COVID-19 pandemic. Individuals of low socioeconomic status (SES) are at an increased risk for COVID-19 infection and severe clinical outcomes. It is unclear if telehealth is a viable continuity of care enabler for the underserved. METHODS: The Weill Cornell Community Clinic (WCCC) implemented a novel telehealth clinic model to serve uninsured patients in May 2020. A phone survey of was conducted to assess WCCC patients access to technology needed for telehealth visits (eg, personal computers, smartphones). Patient no-show rates were retrospectively assessed for both in-person (pre-pandemic) and hybrid continuity of care models. RESULTS: The phone survey found that 90% of WCCC patients had access to technology needed for telehealth visits. In the 8 months following implementation of the hybrid model, telehealth and in-person no-show rates were 11% (14/128) and 15% (10/67) respectively; the combined hybrid no-show rate was 12% (24/195). For comparison, the in-person 2019 no-show rate was 23% (84/367). This study aligns with previous reports that telehealth improves patient attendance. CONCLUSION: Literature on the transition of SRFCs from in-person to telehealth care delivery models is limited. At the WCCC, the reduction in no-show rates supports the feasibility and benefits of adopting telehealth for the delivery of care to underserved patient populations. We believe the hybrid telehealth model described here is a viable model for other student run free clinics to increase access to care in low SES communities.

Stem cells expand potency and alter tissue fitness by accumulating diverse epigenetic memories.

Immune and tissue stem cells retain an epigenetic memory of inflammation that intensifies sensitivity to future encounters. We investigated whether and to what consequence stem cells possess and accumulate memories of diverse experiences. Monitoring a choreographed response to wounds, we found that as hair follicle stem cells leave their niche, migrate to repair damaged epidermis, and take up long-term foreign residence there, they accumulate long-lasting epigenetic memories of each experience, culminating in post-repair epigenetic adaptations that sustain the epidermal transcriptional program and surface barrier. Each memory is distinct, separable, and has its own physiological impact, collectively endowing these stem cells with heightened regenerative ability to heal wounds and broadening their tissue-regenerating tasks relative to their naïve counterparts.

Author Correction: Extracellular serine controls epidermal stem cell fate and tumour initiation.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Extracellular serine controls epidermal stem cell fate and tumour initiation.

Tissue stem cells are the cell of origin for many malignancies. Metabolites regulate the balance between self-renewal and differentiation, but whether endogenous metabolic pathways or nutrient availability predispose stem cells towards transformation remains unknown. Here, we address this question in epidermal stem cells (EpdSCs), which are a cell of origin for squamous cell carcinoma. We find that oncogenic EpdSCs are serine auxotrophs whose growth and self-renewal require abundant exogenous serine. When extracellular serine is limited, EpdSCs activate de novo serine synthesis, which in turn stimulates α-ketoglutarate-dependent dioxygenases that remove the repressive histone modification H3K27me3 and activate differentiation programmes. Accordingly, serine starvation or enforced α-ketoglutarate production antagonizes squamous cell carcinoma growth. Conversely, blocking serine synthesis or repressing α-ketoglutarate-driven demethylation facilitates malignant progression. Together, these findings reveal that extracellular serine is a critical determinant of EpdSC fate and provide insight into how nutrient availability is integrated with stem cell fate decisions during tumour initiation.

irRECIST for the Evaluation of Candidate Biomarkers of Response to Nivolumab in Metastatic Clear Cell Renal Cell Carcinoma: Analysis of a Phase II Prospective Clinical Trial.

PURPOSE: Immune-related RECIST (irRECIST) were designed to capture atypical responses seen with immunotherapy. We hypothesized that, in patients with metastatic clear cell renal cell carcinoma (mccRCC), candidate biomarkers for nivolumab response would show improved association with clinical endpoints capturing atypical responders (irRECIST) compared with standard clinical endpoints (RECISTv1.1). EXPERIMENTAL DESIGN: Endpoints based on RECISTv1.1 [objective response rate (ORR)/progression-free survival (PFS)] or irRECIST [immune-related ORR (irORR)/immune-related PFS (irPFS)] were compared in patients enrolled in the CheckMate-010 trial. Pretreatment tumors were analyzed by PD-L1 and PD-L2 IHC, and by multiplex immunofluorescence for CD8, PD-1, TIM-3, and LAG-3. T-cell activation signatures were assessed by RNA sequencing. RESULTS: Median irPFS was significantly longer than median PFS. irORR was not significantly different from ORR, but immune-related progressive disease (irPD) rate was significantly lower than progressive disease (PD) rate. Tumor cell (TC) PD-L1 expression was not associated with PFS or ORR, but patients with TC PD-L1 ≥1% had longer median irPFS and higher irORR. High percentage of CD8+ tumor-infiltrating cells (TIC) that are PD-1+TIM-3-LAG-3- (% CD8+PD-1+TIM-3-LAG-3- TIC) correlated with high levels of T-cell activation and was associated with longer median irPFS and higher irORR. Notably, combination of TC PD-L1 expression with % CD8+PD-1+TIM-3-LAG-3- TIC identified three groups of patients for which irPFS and irORR were significantly different. CONCLUSIONS: Atypical responders to nivolumab were identified in the CheckMate-010 trial. We observed improved association of candidate biomarkers for nivolumab response with endpoints defined by irRECIST compared with RECISTv1.1. TC PD-L1 expression in combination with PD-1 expression on CD8+ TIC may predict outcome on nivolumab in mccRCC.

Cells Lacking the RB1 Tumor Suppressor Gene Are Hyperdependent on Aurora B Kinase for Survival.

Small cell lung cancer (SCLC) accounts for 15% of lung cancers and is almost always linked to inactivating RB1 and TP53 mutations. SCLC frequently responds, albeit briefly, to chemotherapy. The canonical function of the RB1 gene product RB1 is to repress the E2F transcription factor family. RB1 also plays both E2F-dependent and E2F-independent mitotic roles. We performed a synthetic lethal CRISPR/Cas9 screen in an RB1 -/- SCLC cell line that conditionally expresses RB1 to identify dependencies that are caused by RB1 loss and discovered that RB1 -/- SCLC cell lines are hyperdependent on multiple proteins linked to chromosomal segregation, including Aurora B kinase. Moreover, we show that an Aurora B kinase inhibitor is efficacious in multiple preclinical SCLC models at concentrations that are well tolerated in mice. These results suggest that RB1 loss is a predictive biomarker for sensitivity to Aurora B kinase inhibitors in SCLC and perhaps other RB1 -/- cancers. SIGNIFICANCE: SCLC is rarely associated with actionable protooncogene mutations. We did a CRISPR/Cas9-based screen that showed that RB1 -/- SCLC are hyperdependent on AURKB, likely because both genes control mitotic fidelity, and confirmed that Aurora B kinase inhibitors are efficacious against RB1 -/- SCLC tumors in mice at nontoxic doses.See related commentary by Dick and Li, p. 169.This article is highlighted in the In This Issue feature, p. 151.

HIF activation causes synthetic lethality between the VHL tumor suppressor and the EZH1 histone methyltransferase.

Inactivation of the von Hippel-Lindau tumor suppressor protein (pVHL) is the signature lesion in the most common form of kidney cancer, clear cell renal cell carcinoma (ccRCC). pVHL loss causes the transcriptional activation of hypoxia-inducible factor (HIF) target genes, including many genes that encode histone lysine demethylases. Moreover, chromatin regulators are frequently mutated in this disease. We found that ccRCC displays increased H3K27 acetylation and a shift toward mono- or unmethylated H3K27 caused by an HIF-dependent increase in H3K27 demethylase activity. Using a focused short hairpin RNA library, as well as CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 (CRISPR-associated protein 9) and a pharmacological inhibitor, we discovered that pVHL-defective ccRCC cells are hyperdependent on the H3K27 methyltransferase EZH1 for survival. Therefore, targeting EZH1 could be therapeutically useful in ccRCC.