It is unclear that how subcellular organelles respond to external mechanical stimuli. Here, we investigated the molecular mechanisms by which mechanical force regulates Ca2+ signaling at endoplasmic reticulum (ER) in human mesenchymal stem cells. Without extracellular Ca2+, ER Ca2+ release is the source of intracellular Ca2+ oscillations induced by laser-tweezer-traction at the plasma membrane, providing a model to study how mechanical stimuli can be transmitted deep inside the cell body. This ER Ca2+ release upon mechanical stimulation is mediated not only by the mechanical support of cytoskeleton and actomyosin contractility, but also by mechanosensitive Ca2+ permeable channels on the plasma membrane, specifically TRPM7. However, Ca2+ influx at the plasma membrane via mechanosensitive Ca2+ permeable channels is only mediated by the passive cytoskeletal structure but not active actomyosin contractility. Thus, active actomyosin contractility is essential for the response of ER to the external mechanical stimuli, distinct from the mechanical regulation at the plasma membrane.
The Angiotensin II Type 1 (AT1) receptor is one of the most widely studied GPCRs within the context of biased signaling. While the AT1 receptor is activated by agonists such as the peptide AngII, it can also be activated by mechanical stimuli such as membrane stretch or shear in the absence of a ligand. Despite the importance of mechanical activation of the AT1 receptor in biological processes such as vasoconstriction, little is known about the structural changes induced by external physical stimuli mediated by the surrounding lipid membrane. Here, we present a systematic simulation study that characterizes the activation of the AT1 receptor under various membrane environments and mechanical stimuli. We show that stability of the active state is highly sensitive to membrane thickness and tension. Structural comparison of membrane-mediated vs. agonist-induced activation shows that the AT1 receptor has distinct active conformations. This is supported by multi-microsecond free energy calculations that show unique landscapes for the inactive and various active states. Our modeling results provide structural insights into the mechanical activation of the AT1 receptor and how it may produce different functional outcomes within the framework of biased agonism.
more » « less- NSF-PAR ID:
- 10438762
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 14
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
-
more » « less
Abstract The interaction between TNFα and TNFR1 is essential in maintaining tissue development and immune responses. While TNFR1 is a cell surface receptor, TNFα exists in both soluble and membrane-bound forms. Interestingly, it was found that the activation of TNFR1-mediated signaling pathways is preferentially through the soluble form of TNFα, which can also induce the clustering of TNFR1 on plasma membrane of living cells. We developed a multiscale simulation framework to compare receptor clustering induced by soluble and membrane-bound ligands. Comparing with the freely diffusive soluble ligands, we hypothesize that the conformational dynamics of membrane-bound ligands are restricted, which affects the clustering of ligand-receptor complexes at cell-cell interfaces. Our simulation revealed that only small clusters can form if TNFα is bound on cell surface. In contrast, the clustering triggered by soluble TNFα is more dynamic, and the size of clusters is statistically larger. We therefore demonstrated the impact of membrane-bound ligand on dynamics of receptor clustering. Moreover, considering that larger TNFα-TNFR1 clusters is more likely to provide spatial platform for downstream signaling pathway, our studies offer new mechanistic insights about why the activation of TNFR1-mediated signaling pathways is not preferred by membrane-bound form of TNFα.
-
more » « less
Abstract Stress‐activated signaling pathways orchestrate cellular behaviors and fates. Studying the precise role(s) of stress‐activated protein kinases is challenging, because stress conditions induce adaptation and impose selection pressure. To meet this challenge, we have applied an optogenetic system with a single plasmid to express light‐activated p38α or its upstream activator, MKK6, in conjunction with live‐cell fluorescence microscopy. In starved cells, decaging of constitutively active p38α or MKK6 by brief exposure to UV light elicits rapid p38‐mediated signaling, release of cytochrome c from mitochondria, and apoptosis with different kinetics. In parallel, light activation of p38α also suppresses autophagosome formation, similarly to stimulation with growth factors that activate PI3K/Akt/mTORC1 signaling. Active MKK6 negatively regulates serum‐induced ERK activity, which is p38‐independent as previously reported. Here, we reproduce that result with the one plasmid system and show that although decaging active p38α does not reduce basal ERK activity in our cells, it can block growth factor‐stimulated ERK signaling in serum‐starved cells. These results clarify the roles of MKK6 and p38α in dynamic signaling programs, which act in concert to actuate apoptotic death while suppressing cell survival mechanisms.
-
more » « less
Introduction: The proteins of the Bin/Amphiphysin/Rvs167 (BAR) domain superfamily arebelieved to induce membrane curvature. PICK1 is a distinctive protein that consists of both a BAR anda PDZ domain, and it has been associated with numerous diseases. It is known to facilitate membranecurvature during receptor-mediated endocytosis. In addition to understanding how the BAR domainfacilitates membrane curvature, it's particularly interesting to unravel the hidden links between thestructural and mechanical properties of the PICK1 BAR domain.
Methods: This paper employs steered molecular dynamics (SMD) to investigate the mechanical propertiesassociated with structural changes in the PICK1 BAR domains.
Results: Our findings suggest that not only do helix kinks assist in generating curvature of BAR domains,but they may also provide the additional flexibility required to initiate the binding betweenBAR domains and the membrane
Conclusion: We have observed a complex interaction network within the BAR monomer and at thebinding interface of the two BAR monomers. This network is crucial for maintaining the mechanicalproperties of the BAR dimer. Owing to this interaction network, the PICK1 BAR dimer exhibits differentresponses to external forces applied in opposite directions.
-
more » « less
SUMMARY The sensing of abiotic stress, mechanical injury or pathogen attack by a single plant tissue results in the activation of systemic signals that travel from the affected tissue to the entire plant. This process is essential for plant survival during stress and is termed systemic signaling. Among the different signals triggered during this process are calcium, electric, reactive oxygen species and hydraulic signals. These are thought to propagate at rapid rates through the plant vascular bundles and to regulate many of the systemic processes essential for plant survival. Although the different signals activated during systemic signaling are thought to be interlinked, their coordination and hierarchy still need to be determined. Here, using a combination of advanced whole‐plant imaging and hydraulic pressure measurements, we studied the activation of all four systemic signals in wild‐type and different
Arabidopsis thaliana mutants subjected to a local treatment of high‐light (HL) stress or wounding. Our findings reveal that activation of systemic membrane potential, calcium, reactive oxygen species and hydraulic pressure signals, in response to wounding, is dependent on glutamate receptor‐like proteins 3.3 and 3.6. In contrast, in response to HL stress, systemic changes in calcium and membrane potential depended on glutamate receptor‐like 3.3 and 3.6, while systemic hydraulic signals did not. We further show that plasmodesmata functions are required for systemic changes in membrane potential and calcium during responses to HL stress or wounding. Our findings shed new light on the different mechanisms that integrate different systemic signals in plants during stress.
