28 research outputs found
Ī±1A-Adrenergic Receptor Induces Activation of Extracellular Signal-Regulated Kinase 1/2 through Endocytic Pathway
G protein-coupled receptors (GPCRs) activate mitogen-activated protein kinases through a number of distinct pathways in cells. Increasing evidence has suggested that endosomal signaling has an important role in receptor signal transduction. Here we investigated the involvement of endocytosis in Ī±1A-adrenergic receptor (Ī±1A-AR)-induced activation of extracellular signal-regulated kinase 1/2 (ERK1/2). Agonist-mediated endocytic traffic of Ī±1A-AR was assessed by real-time imaging of living, stably transfected human embryonic kidney 293A cells (HEK-293A). Ī±1A-AR was internalized dynamically in cells with agonist stimulation, and actin filaments regulated the initial trafficking of Ī±1A-AR. Ī±1A-AR-induced activation of ERK1/2 but not p38 MAPK was sensitive to disruption of endocytosis, as demonstrated by 4Ā°C chilling, dynamin mutation and treatment with cytochalasin D (actin depolymerizing agent). Activation of protein kinase C (PKC) and C-Raf by Ī±1A-AR was not affected by 4Ā°C chilling or cytochalasin D treatment. U73122 (a phospholipase C [PLC] inhibitor) and Ro 31ā8220 (a PKC inhibitor) inhibited Ī±1B-AR- but not Ī±1A-AR-induced ERK1/2 activation. These data suggest that the endocytic pathway is involved in Ī±1A-AR-induced ERK1/2 activation, which is independent of Gq/PLC/PKC signaling
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Myosin X is recruited to nascent focal adhesions at the leading edge and induces multi-cycle filopodial elongation
Filopodia protrude from the leading edge of cells and play important roles in cell motility. Here we report the mechanism of myosin X (encoded by Myo10)-induced multi-cycle filopodia extension. We found that actin, Arp2/3, vinculin and integrin-Ī² first accumulated at the cellās leading edge. Myosin X was then gathered at these sites, gradually clustered by lateral movement, and subsequently initiated filopodia formation. During filopodia extension, we found the translocation of Arp2/3 and integrin-Ī² along filopodia. Arp2/3 and integrin-Ī² then became localized at the tip of filopodia, from where myosin X initiated the second extension of filopodia with a change in extension direction, thus producing long filopodia. Elimination of integrin-Ī², Arp2/3 and vinculin by siRNA significantly attenuated the myosin-X-induced long filopodia formation. We propose the following mechanism. Myosin X accumulates at nascent focal adhesions at the cellās leading edge, where myosin X promotes actin convergence to create the base of filopodia. Then myosin X moves to the filopodia tip and attracts integrin-Ī² and Arp2/3 for further actin nucleation. The tip-located myosin X then initiates the second cycle of filopodia elongation to produce the long filopodia
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Scramblase TMEM16F terminates T cell receptor signaling to restrict T cell exhaustion
In chronic infection, T cells become hyporesponsive to antigenic stimulation to prevent immunopathology. Here, we show that TMEM16F is required to curb excessive T cell responses in chronic infection with virus. TMEM16F-deficient T cells are hyperactivated during the early phase of infection, exhibiting increased proliferation and cytokine production. Interestingly, this overactivation ultimately leads to severe T cell exhaustion and the inability of the host to control viral burden. Mechanistically, we identify TMEM16F as the dominant lipid scramblase in T lymphocytes that transports phospholipids across membranes. TMEM16F is located in late endosomes, where it facilitates the generation of multivesicular bodies for TCR degradation and signal termination. Consequently, TMEM16F deficiency results in sustained signaling and augmented T cell activation. Our results demonstrate that scramblase restricts TCR responses to avoid overactivation, ensuring a well-balanced immune response in chronic infectious disease
Dynamics of phosphoinositide conversion in clathrin-mediated endocytic traffic
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