No abstract

Phosphorylation of G protein-coupled receptors (GPCR) by GPCR kinases (GRKs) desensitizes G protein signaling and promotes arrestin signaling, which is also modulated by biased ligands 1-6 . Molecular assembly of GRKs to GPCRs and the basis of GRK-mediated biased signaling remain largely unknown due to the weak GPCR-GRK interactions. Here we report the complex structure of neurotensin receptor 1 (NTSR1) bound to GRK2, Gαq, and an arrestin-biased ligand, SBI-553 7 , at a resolution of 2.92 Å. The high-quality density map reveals the clear arrangement of the intact GRK2 with the receptor, with the N-terminal helix of GRK2 docking into the open cytoplasmic pocket formed by the outward movement of the receptor TM6, analogous of the binding of G protein to the receptor. Strikingly, the arrestin-biased ligand is found at the interface between GRK2 and NTSR1 to enhance GRK2 binding. The binding mode of the biased ligand is compatible with arrestin binding but is clashed with the binding of a G protein, thus provide an unambiguous mechanism for its arrestin-biased signaling capability. Together, our structure provides a solid model for understanding the details of GPCR-GRK interactions and biased signaling.GPCRs comprise the largest family of cell surface receptors whose signaling is primarily mediated by two types of downstream effectors: G-proteins and arrestins.The switch of GPCR signaling from G-protein pathways to arrestin pathways is controlled by a small family of GPCR kinases, GRKs, which phosphorylate either the receptor C-terminal tail or the third intracellular loop (ICL3) 1-3 . Phosphorylation of GPCRs promotes recruitment of arrestin, which blocks G-protein binding and desensitizes G-protein signaling 3 . Because drugs that selectively activate either Gprotein pathways or arrestin pathways (biased signaling) are proposed to have better therapeutic and safety index 4,5 , the mechanism of GPCR biased signaling has been a subject of intensive research over the past two decades.

Background/purpose Dental pulp stem cells can be isolated from human teeth with deep caries (cDPSCs), but their biological characteristics are still unclear. The aim of this study was to investigate the angiogenic potential of cDPSCs and compare them to dental pulp stem cells from human normal teeth (nDPSCs). Materials and methods Cells were isolated from human pulp tissue of normal and infected teeth with deep caries. Basic mesenchymal stem cell (MSC) characterization was conducted. Colony forming units and proliferation ability were evaluated in nDPSCs and cDPSCs. Expression of VEGF in both tissues and cells was examined by immunohistochemical staining. After stimulating nDPSCs and cDPSCs with an angiogenic medium, angiogenic markers were evaluated by qRT-PCR and western blotting. Finally, tube formation assays were used to evaluate the in vitro angiogenesis potential of both cell populations. Results Both nDPSCs and cDPSCs possessed typical MSC characteristics. cDPSCs had enhanced colony formation and proliferation capacities than nDPSCs did. The expression of VEGF was higher in pulp tissue from teeth with deep caries and cDPSCs than in normal tissue and nDPSCs. When both cell types were grown in vitro under angiogenic conditions, cDPSCs expressed a higher level of angiogenic markers and showed a stronger angiogenesis potential than nDPSCs did. Conclusion cDPSCs maintained MSC traits and presented a higher angiogenesis potential than nDPSCs.