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Notch2 complements Notch1 to mediate inductive signaling that initiates early T cell development.

ABSTRACT: Notch signaling is the dominant intercellular signaling input during the earliest stages of T cell development in the thymus. Although Notch1 is known to be indispensable, we show that it does not mediate all Notch signaling in precommitment stages: Notch2 initially works in parallel to promote early murine T cell development and antagonize other fates. Notch-regulated target genes before and after T lineage commitment change dynamically, and we show that this partially reflects shifts in genome-wide DNA binding by RBPJ, the transcription factor activated by complex formation with the Notch intracellular domain. Although Notch signaling and transcription factor PU.1 can activate some common targets in precommitment T progenitors, Notch signaling and PU.1 activity have functionally antagonistic effects on multiple targets, delineating separation of pro-T cells from alternative PU.1-dependent fates. These results define a distinct mechanism of Notch signal response that distinguishes the initial stages of murine T cell development.

SUBMITTER: Romero-Wolf M

PROVIDER: S-EPMC7659720 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

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Notch2 complements Notch1 to mediate inductive signaling that initiates early T cell development.

Romero-Wolf Maile M Shin Boyoung B Zhou Wen W Koizumi Maria M Rothenberg Ellen V EV Hosokawa Hiroyuki H

The Journal of cell biology 20201001 10

Notch signaling is the dominant intercellular signaling input during the earliest stages of T cell development in the thymus. Although Notch1 is known to be indispensable, we show that it does not mediate all Notch signaling in precommitment stages: Notch2 initially works in parallel to promote early murine T cell development and antagonize other fates. Notch-regulated target genes before and after T lineage commitment change dynamically, and we show that this partially reflects shifts in genome ...[more]

PMID: 32756905

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Project description:BackgroundNotch receptors are normally cleaved during maturation by a furin-like protease at an extracellular site termed S1, creating a heterodimer of non-covalently associated subunits. The S1 site lies within a key negative regulatory region (NRR) of the receptor, which contains three highly conserved Lin12/Notch repeats and a heterodimerization domain (HD) that interact to prevent premature signaling in the absence of ligands. Because the role of S1 cleavage in Notch signaling remains unresolved, we investigated the effect of S1 cleavage on the structure, surface trafficking and ligand-mediated activation of human Notch1 and Notch2, as well as on ligand-independent activation of Notch1 by mutations found in human leukemia.Principal findingsThe X-ray structure of the Notch1 NRR after furin cleavage shows little change when compared with that of an engineered Notch1 NRR lacking the S1-cleavage loop. Likewise, NMR studies of the Notch2 HD domain show that the loop containing the S1 site can be removed or cleaved without causing a substantial change in its structure. However, Notch1 and Notch2 receptors engineered to resist S1 cleavage exhibit unexpected differences in surface delivery and signaling competence: S1-resistant Notch1 receptors exhibit decreased, but detectable, surface expression and ligand-mediated receptor activation, whereas S1-resistant Notch2 receptors are fully competent for cell surface delivery and for activation by ligands. Variable dependence on S1 cleavage also extends to T-ALL-associated NRR mutations, as common class 1 mutations display variable decrements in ligand-independent activation when introduced into furin-resistant receptors, whereas a class 2 mutation exhibits increased signaling activity.Conclusions/significanceS1 cleavage has distinct effects on the surface expression of Notch1 and Notch2, but is not generally required for physiologic or pathophysiologic activation of Notch proteins. These findings are consistent with models for receptor activation in which ligand-binding or T-ALL-associated mutations lead to conformational changes of the NRR that permit metalloprotease cleavage.

Project description:Pulmonary arterial hypertension (PAH) is a fatal cardiopulmonary disease characterized by increased vascular cell proliferation with apoptosis resistance and occlusive remodeling of the small pulmonary arteries. The Notch family of proteins subserves proximal signaling of an evolutionarily conserved pathway that effects cell proliferation, fate determination, and development. In endothelial cells (ECs), Notch receptor 2 (Notch2) was shown to promote endothelial apoptosis. However, a pro- or antiproliferative role for Notch2 in pulmonary endothelial proliferation and ensuing PAH is unknown. We postulated that suppressed Notch2 signaling drives pulmonary endothelial proliferation in the context of PAH. We observed that levels of Notch2 are ablated in lungs from PAH subjects compared with non-PAH controls. Notch2 expression was attenuated in human pulmonary artery endothelial cells (hPAECs) exposed to vasoactive stimuli including hypoxia, TGF-β, ET-1, and IGF-1. Notch2-deficient hPAECs activated Akt, Erk1/2, and antiapoptotic protein Bcl-2 and reduced levels of p21cip and Bax associated with increased EC proliferation and reduced apoptosis. In addition, Notch2 suppression elicited a paradoxical activation of Notch1 and canonical Notch target gene Hes1, Hey1, and Hey2 transcription. Furthermore, reduction in Rb and increased E2F1 binding to the Notch1 promoter appear to explain the Notch1 upregulation. Yet, when Notch1 was decreased in Notch2-suppressed cells, the wound injury response was augmented. In aggregate, our results demonstrate that loss of Notch2 in hPAECs derepresses Notch1 and elicits EC hallmarks of PAH. Augmented EC proliferation upon Notch1 knockdown points to a context-dependent role for Notch1 and 2 in endothelial cell homeostasis.NEW & NOTEWORTHY This study demonstrates a previously unidentified role for Notch2 in the maintenance of lung vascular endothelial cell quiescence and pulmonary artery hypertension (PAH). A key novel finding is that Notch2 suppression activates Notch1 via Rb-E2F1-mediated signaling and induces proliferation and apoptosis resistance in human pulmonary artery endothelial cells. Notably, PAH patients show reduced levels of endothelial Notch2 in their pulmonary arteries, supporting Notch2 as a fundamental driver of PAH pathogenesis.

Dataset Information

Notch2 complements Notch1 to mediate inductive signaling that initiates early T cell development.

Publications

Notch2 complements Notch1 to mediate inductive signaling that initiates early T cell development.

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