Corrigendum: Rare cell variability and drug-induced reprogramming as a mode of cancer drug resistance.

This corrects the article DOI: 10.1038/nature22794.

Rare cell variability and drug-induced reprogramming as a mode of cancer drug resistance.

Therapies that target signalling molecules that are mutated in cancers can often have substantial short-term effects, but the emergence of resistant cancer cells is a major barrier to full cures. Resistance can result from secondary mutations, but in other cases there is no clear genetic cause, raising the possibility of non-genetic rare cell variability. Here we show that human melanoma cells can display profound transcriptional variability at the single-cell level that predicts which cells will ultimately resist drug treatment. This variability involves infrequent, semi-coordinated transcription of a number of resistance markers at high levels in a very small percentage of cells. The addition of drug then induces epigenetic reprogramming in these cells, converting the transient transcriptional state to a stably resistant state. This reprogramming begins with a loss of SOX10-mediated differentiation followed by activation of new signalling pathways, partially mediated by the activity of the transcription factors JUN and/or AP-1 and TEAD. Our work reveals the multistage nature of the acquisition of drug resistance and provides a framework for understanding resistance dynamics in single cells. We find that other cell types also exhibit sporadic expression of many of these same marker genes, suggesting the existence of a general program in which expression is displayed in rare subpopulations of cells.

Intercellular mRNA trafficking via membrane nanotube-like extensions in mammalian cells.

RNAs have been shown to undergo transfer between mammalian cells, although the mechanism behind this phenomenon and its overall importance to cell physiology is not well understood. Numerous publications have suggested that RNAs (microRNAs and incomplete mRNAs) undergo transfer via extracellular vesicles (e.g., exosomes). However, in contrast to a diffusion-based transfer mechanism, we find that full-length mRNAs undergo direct cell-cell transfer via cytoplasmic extensions characteristic of membrane nanotubes (mNTs), which connect donor and acceptor cells. By employing a simple coculture experimental model and using single-molecule imaging, we provide quantitative data showing that mRNAs are transferred between cells in contact. Examples of mRNAs that undergo transfer include those encoding GFP, mouse ß-actin, and human Cyclin D1, BRCA1, MT2A, and HER2. We show that intercellular mRNA transfer occurs in all coculture models tested (e.g., between primary cells, immortalized cells, and in cocultures of immortalized human and murine cells). Rapid mRNA transfer is dependent upon actin but is independent of de novo protein synthesis and is modulated by stress conditions and gene-expression levels. Hence, this work supports the hypothesis that full-length mRNAs undergo transfer between cells through a refined structural connection. Importantly, unlike the transfer of miRNA or RNA fragments, this process of communication transfers genetic information that could potentially alter the acceptor cell proteome. This phenomenon may prove important for the proper development and functioning of tissues as well as for host-parasite or symbiotic interactions.

Association of Suicide Prevention Interventions With Subsequent Suicide Attempts, Linkage to Follow-up Care, and Depression Symptoms for Acute Care Settings: A Systematic Review and Meta-analysis.

Importance: To prevent suicide deaths, acute care settings need tools to ensure individuals at risk of suicide access mental health care and remain safe until they do so. Objective: To examine the association of brief acute care suicide prevention interventions with patients' subsequent suicide attempts, linkage to follow-up care, and depression symptoms at follow-up. Data Sources: Ovid MEDLINE, Scopus, CINAHL, PsychINFO, Embase, and references of included studies using concepts of suicide, prevention, and clinical trial to identify relevant articles published January 2000 to May 2019. Study Selection: Studies describing clinical trials of single-encounter suicide prevention interventions were included. Two reviewers independently reviewed all articles to determine eligibility for study inclusion. Data Extraction and Synthesis: Two reviewers independently abstracted data according to PRISMA guidelines and assessed studies' risk of bias using the Cochrane Risk of Bias tool. Data were pooled for each outcome using random-effects models. Small study effects including publication bias were assessed using Peter and Egger regression tests. Main Outcomes and Measures: Three primary outcomes were examined: subsequent suicide attempts, linkage to follow-up care, and depression symptoms at follow-up. Suicide attempts and linkage to follow-up care were measured using validated patient self-report measures and medical record review; odds ratios and Hedges g standardized mean differences were pooled to estimate effect sizes. Depression symptoms were measured 2 to 3 months after the encounter using validated self-report measures, and pooled Hedges g standardized mean differences were used to estimate effect sizes. Results: A total of 14 studies, representing outcomes for 4270 patients, were included. Pooled-effect estimates showed that brief suicide prevention interventions were associated with reduced subsequent suicide attempts (pooled odds ratio, 0.69; 95% CI, 0.53-0.89), increased linkage to follow-up (pooled odds ratio, 3.04; 95% CI, 1.79-5.17) but were not associated with reduced depression symptoms (Hedges g = 0.28 [95% CI, -0.02 to 0.59). Conclusions and Relevance: In this meta-analysis, breif suicide prevention interventions were associated with reduced subsequent suicide attempts. Suicide prevention interventions delivered in a single in-person encounter may be effective at reducing subsequent suicide attempts and ensuring that patients engage in follow-up mental health care.

Intravascular Stem Cell Bioreactor for Prevention of Adverse Remodeling After Myocardial Infarction.

Background Prevention of adverse remodeling after myocardial infarction (MI) is an important goal of stem cell therapy. Clinical trial results vary, however, and poor cell retention and survival after delivery likely limit the opportunity to exert beneficial effects. To overcome these limitations, we built an implantable intravascular bioreactor (IBR) designed to protect contained cells from washout, dilution, and immune attack while allowing sustained release of beneficial paracrine factors. Methods and Results IBRs were constructed using semipermeable membrane adhered to a clinical-grade catheter shaft. Mesenchymal stem cell (MSC) viability in and paracrine factor release from IBRs were assessed in vitro and IBR biocompatibility and immune protection confirmed in vivo. In a porcine anterior MI model, IBRs containing 25 million allogeneic MSCs (IBR-MSCs) were compared with IBRs containing media alone (IBR-Placebo; n=8 per group) with adverse remodeling assessed by magnetic resonance imaging. Four weeks after MI, IBR-MSCs had no significant change in end-diastolic volume (+0.33±4.32 mL; P=0.89), end-systolic volume (+2.14±4.13 mL; P=0.21), and left ventricular ejection fraction (-2.27±2.94; P=0.33) while IBR-Placebo had significant increases in end-diastolic volume (+10.37±3.84 mL; P=0.01) and ESV (+11.35±2.88 mL; P=0.01), and a significant decrease in left ventricular ejection fraction (-5.78±1.70; P=0.025). Eight weeks after MI, adherent pericarditis was present in 0 of 8 IBR-MSCs versus 4 of 8 IBR-Placebo (P=0.02), suggesting an anti-inflammatory effect. In a separate study, 25 million allogeneic pig MSCs directly injected in the peri-infarct zone 3 days after MI (n=6) showed no significant benefit in adverse remodeling at 4 weeks compared with IBR-MSCs. Conclusions MSCs deployed inside an implantable, removable, and potentially rechargeable bioreactor in a large animal model remain viable, are immunoprotected, and attenuate adverse remodeling 4 weeks after MI.