Structure of the human smoothened receptor bound to an antitumour agent.
ABSTRACT The smoothened (SMO) receptor, a key signal transducer in the hedgehog signalling pathway, is responsible for the maintenance of normal embryonic development and is implicated in carcinogenesis. It is classified as a class frizzled (class F) G-protein-coupled receptor (GPCR), although the canonical hedgehog signalling pathway involves the GLI transcription factors and the sequence similarity with class A GPCRs is less than 10%. Here we report the crystal structure of the transmembrane domain of the human SMO receptor bound to the small-molecule antagonist LY2940680 at 2.5 Å resolution. Although the SMO receptor shares the seven-transmembrane helical fold, most of the conserved motifs for class A GPCRs are absent, and the structure reveals an unusually complex arrangement of long extracellular loops stabilized by four disulphide bonds. The ligand binds at the extracellular end of the seven-transmembrane-helix bundle and forms extensive contacts with the loops.
SourceAvailable from: Ramon Whitson[Show abstract] [Hide abstract]
ABSTRACT: Advanced basal cell carcinomas (BCCs) frequently acquire resistance to Smoothened (SMO) inhibitors through unknown mechanisms. Here we identify SMO mutations in 50% (22 of 44) of resistant BCCs and show that these mutations maintain Hedgehog signaling in the presence of SMO inhibitors. Alterations include four ligand binding pocket mutations defining sites of inhibitor binding and four variants conferring constitutive activity and inhibitor resistance, illuminating pivotal residues that ensure receptor autoinhibition. In the presence of a SMO inhibitor, tumor cells containing either class of SMO mutants effectively outcompete cells containing the wild-type SMO. Finally, we show that both classes of SMO variants respond to aPKC-ι/λ or GLI2 inhibitors that operate downstream of SMO, setting the stage for the clinical use of GLI antagonists. Copyright © 2015 Elsevier Inc. All rights reserved.
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ABSTRACT: The Hedgehog (Hh) signalling pathway plays a pivotal role in the spatial and temporal regulation of cell proliferation and differentiation. By controlling the correct maturation of developing tissues and ensuring attainment of the correct size, position and the presence of fully functioning cellular structures, the Hh plays a pivotal role in development. Conversely aberrant Hh signalling is involved in Gorlin syndrome, basal cell carcinoma (the most common cancer in the world), and more than one third of all human medulloblastoma cases. In all of these cases, it is believed that deregulated Hh signalling leads to increased cell proliferation and tumour formation. Inhibition of the Hedgehog signalling pathway, is a recently validated anti-cancer drug target, with vismodegib (Erivedge™), approved by the U.S. Food and Drug Administration for the treatment of adult basal cell carcinoma. In this perspective we outline the current state of Hh pathway inhibitors with a particular focus on potential limitations of upstream Hh pathway inhibition in relation to resistance mutations and crosstalk pathways. Together, these limitations indicate that inhibition of downstream components, specifically the Gli family of transcription factors, may represent a next generation approach to suppress tumours associated with aberrant Hh pathway signalling.Medicinal Chemistry Communication 01/2014; 5(2):117. DOI:10.1039/c3md00334e · 2.63 Impact Factor
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ABSTRACT: Intramolecular remote coupling within the polypeptide backbones of membrane proteins is difficult to analyze owing to the limited structural information available at the atomic level. Nonetheless, recent progress in the crystallographic study of G protein-coupled receptors (GPCRs) has provided an unprecedented opportunity for understanding the sophisticated architecture of heptahelical transmembrane (7TM) bundles. These 7TM bundles can respond to a wide range of extracellular stimuli while retaining the common function of binding trimeric G proteins. Here we have systematically analyzed select sets of inactive-like 7TM bundles to highlight the structural conservation of the receptors, in terms of intramolecular Cα-Cα distances. Distances with the highest scores were found to be dominated by the intrahelical distances of helix III, regardless of the choice of bundles in the set, indicating that the intracellular half of this helix is highly conserved. Unexpectedly, the distances between the cytoplasmic side of helix I and the extracellular region of helix VI provided the largest contribution to the high score populations among the interhelical pairs in most of the selected sets, including class B, C and frizzled receptors. These findings are expected to be valuable in further studies of GPCRs with unknown structure and of other protein families.