Explore the vast range of titles available.

Notch signaling plays various roles in cell-fate specification through direct cell–cell interactions. Notch receptors are evolutionarily conserved transmembrane proteins with multiple epidermal growth factor (EGF)-like repeats. Drosophila Notch has 36 EGF-like repeats, and while some play a role in Notch signaling, the specific functions of most remain unclear. To investigate the role of each EGF-like repeat, we used 19 previously identified missense mutations of Notch with unique amino acid substitutions in various EGF-like repeats and a transmembrane domain; 17 of these were identified through a single genetic screen. We assessed these mutants’ phenotypes in the nervous system and hindgut during embryogenesis, and found that 10 of the 19 Notch mutants had defects in both lateral inhibition and inductive Notch signaling, showing context dependency. Of these 10 mutants, six accumulated Notch in the endoplasmic reticulum (ER), and these six were located in EGF-like repeats 8–10 or 25. Mutations with cysteine substitutions were not always coupled with ER accumulation. This suggests that certain EGF-like repeats may be particularly susceptible to structural perturbation, resulting in a misfolded and inactive Notch product that accumulates in the ER. Thus, we propose that these EGF-like repeats may be integral to Notch folding.

β-Amyloid peptides, which are derived from amyloid precursor protein (APP), form the plaques in the brain that are characteristic of Alzheimer's disease. Zhou et al. report a high-resolution structure of a transmembrane segment of APP bound to human γ-secretase, the transmembrane protease that cleaves APP to give β-amyloid peptides (see the Perspective by Lichtenthaler and Güner). Disease-associated mutations within presenilin-1, the catalytic subunit of APP, likely affect how the substrate is bound and thus which peptides are generated, with some being more amyloidogenic. It may now be possible to exploit the features of substrate binding to design inhibitors. Science , this issue p. eaaw0930 ; see also p. 690 A view of how the substrate is recognized facilitates understanding of Alzheimer’s disease–associated mutations in γ-secretase. Cleavage of amyloid precursor protein (APP) by the intramembrane protease γ-secretase is linked to Alzheimer’s disease (AD). We report an atomic structure of human γ-secretase in complex with a transmembrane (TM) APP fragment at 2.6-angstrom resolution. The TM helix of APP closely interacts with five surrounding TMs of PS1 (the catalytic subunit of γ-secretase). A hybrid β sheet, which is formed by a β strand from APP and two β strands from PS1, guides γ-secretase to the scissile peptide bond of APP between its TM and β strand. Residues at the interface between PS1 and APP are heavily targeted by recurring mutations from AD patients. This structure, together with that of γ-secretase bound to Notch, reveal contrasting features of substrate binding, which may be applied toward the design of substrate-specific inhibitors.

In a mouse model of small-cell lung cancer and in human tumours, activation of the Notch pathway can lead to a cell fate switch of neuroendocrine cells to less proliferative non-neuroendocrine cells, generating intratumoural heterogeneity. Notch signalling assists tumour growth Small-cell lung cancers (SCLCs) with a neuroendocrine phenotype are aggressive tumours. In a mouse model of SCLC, Julien Sage and colleagues now show that activation of the Notch pathway can lead to cell fate switch of neuroendocrine cells to less proliferative non-neuroendocrine cells, generating intra-tumour heterogeneity. Non-neuroendocrine cells with activated Notch signalling in turn provide trophic support for neuroendocrine cells. Thus neuroendocrine tumour cells create their niche environment, which produces factors that act on neuroendocrine cells and promote tumour growth. Accordingly, targeting neuroendocrine cells with chemotherapeutics and non-neuroendocrine cells with Notch inhibitors cooperate in reducing tumorigenesis. This study sheds new light on the mechanisms underlying intratumoural heterogeneity in lung cancer and suggests that new combination treatments could be used to target SCLCs. The Notch signalling pathway mediates cell fate decisions 1 , 2 and is tumour suppressive or oncogenic depending on the context 2 , 3 . During lung development, Notch pathway activation inhibits the differentiation of precursor cells to a neuroendocrine fate 4 , 5 , 6 . In small-cell lung cancer, an aggressive neuroendocrine lung cancer 7 , loss-of-function mutations in NOTCH genes and the inhibitory effects of ectopic Notch activation indicate that Notch signalling is tumour suppressive 8 , 9 . Here we show that Notch signalling can be both tumour suppressive and pro-tumorigenic in small-cell lung cancer. Endogenous activation of the Notch pathway results in a neuroendocrine to non-neuroendocrine fate switch in 10–50% of tumour cells in a mouse model of small-cell lung cancer and in human tumours. This switch is mediated in part by Rest (also known as Nrsf), a transcriptional repressor that inhibits neuroendocrine gene expression. Non-neuroendocrine Notch-active small-cell lung cancer cells are slow growing, consistent with a tumour-suppressive role for Notch, but these cells are also relatively chemoresistant and provide trophic support to neuroendocrine tumour cells, consistent with a pro-tumorigenic role. Importantly, Notch blockade in combination with chemotherapy suppresses tumour growth and delays relapse in pre-clinical models. Thus, small-cell lung cancer tumours generate their own microenvironment via activation of Notch signalling in a subset of tumour cells, and the presence of these cells may serve as a biomarker for the use of Notch pathway inhibitors in combination with chemotherapy in select patients with small-cell lung cancer.

Key Points Small-cell lung cancer (SCLC) is a deadly cancer associated with smoke exposure that has neuroendocrine (NE) cell properties and is pathologically, molecularly, biologically and clinically very different from other lung cancers. While most patients with SCLC respond initially to cytotoxic therapy, almost all tumours recur and are resistant to further therapy. The mortality is very high, resulting in SCLC being designated as a recalcitrant cancer. As tumours in patients with SCLC are seldom resected, tumour materials for research are scant, resulting in a major barrier for translational research. The initiating molecular events are believed to be inactivation of TP53 and RB1 , which mainly occurs in NE cells in the respiratory epithelium, although many other genes and signalling pathways are disrupted, especially Notch signalling. For the past 30 years, there have been no important clinical developments or approved, effective conventional or targeted therapies for SCLC. There are no effective methods for early detection or prevention (other than smoking avoidance). However, recently there has been an awakening of interest and funding, resulting in the identification of many promising therapeutic approaches, some of which are already in clinical trials. Thus, while the past has been bleak, the future offers greater promise. Small-cell lung cancer is an aggressive form of lung cancer and has been difficult to treat due to therapy resistance. This Review discusses challenges and recent advances in uncovering molecular changes that allow potentially efficient therapies. Small-cell lung cancer (SCLC) is a deadly tumour accounting for approximately 15% of lung cancers and is pathologically, molecularly, biologically and clinically very different from other lung cancers. While the majority of tumours express a neuroendocrine programme (integrating neural and endocrine properties), an important subset of tumours have low or absent expression of this programme. The probable initiating molecular events are inactivation of TP53 and RB1 , as well as frequent disruption of several signalling networks, including Notch signalling. SCLC, when diagnosed, is usually widely metastatic and initially responds to cytotoxic therapy but nearly always rapidly relapses with resistance to further therapies. There were no important therapeutic clinical advances for 30 years, leading SCLC to be designated a 'recalcitrant cancer'. Scientific studies are hampered by a lack of tissue availability. However, over the past 5 years, there has been a worldwide resurgence of studies on SCLC, including comprehensive molecular analyses, the development of relevant genetically engineered mouse models and the establishment of patient-derived xenografts. These studies have led to the discovery of new potential therapeutic vulnerabilities for SCLC and therefore to new clinical trials. Thus, while the past has been bleak, the future offers greater promise.

The NOTCH gene was identified approximately 110 years ago. Classical studies have revealed that NOTCH signaling is an evolutionarily conserved pathway. NOTCH receptors undergo three cleavages and translocate into the nucleus to regulate the transcription of target genes. NOTCH signaling deeply participates in the development and homeostasis of multiple tissues and organs, the aberration of which results in cancerous and noncancerous diseases. However, recent studies indicate that the outcomes of NOTCH signaling are changeable and highly dependent on context. In terms of cancers, NOTCH signaling can both promote and inhibit tumor development in various types of cancer. The overall performance of NOTCH-targeted therapies in clinical trials has failed to meet expectations. Additionally, NOTCH mutation has been proposed as a predictive biomarker for immune checkpoint blockade therapy in many cancers. Collectively, the NOTCH pathway needs to be integrally assessed with new perspectives to inspire discoveries and applications. In this review, we focus on both classical and the latest findings related to NOTCH signaling to illustrate the history, architecture, regulatory mechanisms, contributions to physiological development, related diseases, and therapeutic applications of the NOTCH pathway. The contributions of NOTCH signaling to the tumor immune microenvironment and cancer immunotherapy are also highlighted. We hope this review will help not only beginners but also experts to systematically and thoroughly understand the NOTCH signaling pathway.

Long noncoding RNAs (lncRNAs) play important roles in various biological processes such as proliferation, cell death and differentiation. Here, we show that a liver-enriched lncRNA, named liver fibrosis-associated lncRNA1 (lnc-LFAR1), promotes liver fibrosis. We demonstrate that lnc-LFAR1 silencing impairs hepatic stellate cells (HSCs) activation, reduces TGFβ-induced hepatocytes apoptosis in vitro and attenuates both CCl 4 - and bile duct ligation-induced liver fibrosis in mice. Lnc-LFAR1 promotes the binding of Smad2/3 to TGFβR1 and its phosphorylation in the cytoplasm. Lnc-LFAR1 binds directly to Smad2/3 and promotes transcription of TGFβ, Smad2, Smad3, Notch2 and Notch3 which, in turn, results in TGFβ and Notch pathway activation. We show that the TGFβ1/Smad2/3/lnc-LFAR1 pathway provides a positive feedback loop to increase Smad2/3 response and a novel link connecting TGFβ with Notch pathway. Our work identifies a liver-enriched lncRNA that regulates liver fibrogenesis and suggests it as a potential target for fibrosis treatment. Activated hepatic stellate cells are the principal contributors to liver fibrosis by secreting a variety of pro-fibrogenic cytokines . Here Zhang et al. demonstrate that a liver-enriched lncRNA, lnc-LFAR1, promotes liver fibrosis and HSC activation by activating TGFβ and Notch signaling.

After influenza infection, lineage-negative epithelial progenitors (LNEPs) exhibit a binary response to reconstitute epithelial barriers: activating a Notch-dependent ΔNp63/cytokeratin 5 (Krt5) remodelling program or differentiating into alveolar type II cells (AEC2s). Here we show that local lung hypoxia, through hypoxia-inducible factor (HIF1α), drives Notch signalling and Krt5 pos basal-like cell expansion. Single-cell transcriptional profiling of human AEC2s from fibrotic lungs revealed a hypoxic subpopulation with activated Notch, suppressed surfactant protein C (SPC), and transdifferentiation toward a Krt5 pos basal-like state. Activated murine Krt5 pos LNEPs and diseased human AEC2s upregulate strikingly similar core pathways underlying migration and squamous metaplasia. While robust, HIF1α-driven metaplasia is ultimately inferior to AEC2 reconstitution in restoring normal lung function. HIF1α deletion or enhanced Wnt/β-catenin activity in Sox2 pos LNEPs blocks Notch and Krt5 activation, instead promoting rapid AEC2 differentiation and migration and improving the quality of alveolar repair. Xi et al.  show that after influenza infection, hypoxia drives Notch signalling to expand Krt5 + basal-like cells in the lung. On HIF1α loss, epithelial progenitors directly differentiate into alveolar type II cells and promote functional regeneration.

Our kidneys play a critical role in keeping us healthy, a fact of which we are reminded several times each day. This organ's cellular complexity has hindered progress in understanding the mechanisms underlying chronic kidney disease, which affects 10% of the world's population. Using single-cell transcriptional profiling, Park et al. produced a comprehensive cell atlas of the healthy mouse kidney (see the Perspective by Humphreys). An unexpected cell type in the collecting duct appears to be a transitional state between two known cell types. The transition from one cell type to the other is regulated by the Notch signaling pathway and is associated with metabolic acidosis. The authors also find that genetically distinct kidney diseases with common clinical features share common cellular origins. Science , this issue p. 758 ; see also p. 709 A single-cell atlas of the mouse kidney reveals an unexpected cell type that likely contributes to kidney disease. Our understanding of kidney disease pathogenesis is limited by an incomplete molecular characterization of the cell types responsible for the organ’s multiple homeostatic functions. To help fill this knowledge gap, we characterized 57,979 cells from healthy mouse kidneys by using unbiased single-cell RNA sequencing. On the basis of gene expression patterns, we infer that inherited kidney diseases that arise from distinct genetic mutations but share the same phenotypic manifestation originate from the same differentiated cell type. We also found that the collecting duct in kidneys of adult mice generates a spectrum of cell types through a newly identified transitional cell. Computational cell trajectory analysis and in vivo lineage tracing revealed that intercalated cells and principal cells undergo transitions mediated by the Notch signaling pathway. In mouse and human kidney disease, these transitions were shifted toward a principal cell fate and were associated with metabolic acidosis.

Intrinsically disordered regions (IDRs) play important roles in proteins that regulate gene expression. A prominent example is the intracellular domain of the Notch receptor (NICD), which regulates the transcription of Notch-responsive genes. The NICD sequence includes an intrinsically disordered RAM region and a conserved ankyrin (ANK) domain. The 111-residue RAM region mediates bivalent interactions of NICD with the transcription factor CSL. Although the sequence of RAM is poorly conserved, the linear patterning of oppositely charged residues shows minimal variation. The conformational properties of polyampholytic IDRs are governed as much by linear charge patterning as by overall charge content. Here, we used sequence design to assess how changing the charge patterning within RAM affects its conformational properties, the affinity of NICD to CSL, and Notch transcriptional activity. Increased segregation of oppositely charged residues leads to linear decreases in the global dimensions of RAM and decreases the affinity of a construct including a C-terminal ANK domain (RAMANK) for CSL. Increasing charge segregation from WT RAM sharply decreases transcriptional activation for all permutants. Activation also decreases for some, but not all, permutants with low charge segregation, although there is considerable variation. Our results suggest that the RAM linker is more than a passive tether, contributing local and/or long-range sequence features that modulate interactions within NICD and with downstream components of the Notch pathway. We propose that sequence features within IDRs have evolved to ensure an optimal balance of sequence-encoded conformational properties, interaction strengths, and cellular activities.

Macrophages engulf damaged and dead cells to clear infection, but they also participate in tissue regeneration. Chakrabarti et al. expand the macrophage repertoire for mammary gland development (see the Perspective by Kannan and Eaves). Mammary gland stem cells secrete the Notch ligand Dll1 and activate Notch signaling, which promotes survival of adjacent macrophages. This stimulates production of Wnt ligands, which signal back to the mammary gland stem cells. This cross-talk plays an important role in coordinating mammary gland development, tissue homeostasis, and, not least, breast cancer. Science , this issue p. eaan4153 ; see also p. 1401 Cross-talk between mammary stem cells and macrophages involves Notch and Wnt to regulate mammary development and function. The stem cell niche is a specialized environment that dictates stem cell function during development and homeostasis. We show that Dll1, a Notch pathway ligand, is enriched in mammary gland stem cells (MaSCs) and mediates critical interactions with stromal macrophages in the surrounding niche in mouse models. Conditional deletion of Dll1 reduced the number of MaSCs and impaired ductal morphogenesis in the mammary gland. Moreover, MaSC-expressed Dll1 activates Notch signaling in stromal macrophages, increasing their expression of Wnt family ligands such as Wnt3, Wnt10A, and Wnt16, thereby initiating a feedback loop that promotes the function of Dll1-expressing MaSCs. Together, these findings reveal functionally important cross-talk between MaSCs and their macrophageal niche through Dll1-mediated Notch signaling.