Little is known about the large ectodomain of MET, the product of the c-met protooncogene and receptor for hepatocyte growth factor͞scatter factor (HGF͞SF). Here, we establish by deletion mutagenesis that the HGF͞SF and heparin-binding sites of MET are contained within a large N-terminal domain spanning the ␣-chain (amino acids 25-307) and the first 212 amino acids of the ␤-chain (amino acids 308 -519). Neither the cystine-rich domain (amino acids 520 -561) nor the C-terminal half of MET (amino acids 562-932) bind HGF͞SF or heparin directly. The MET ectodomain, which behaves as a rod-shaped monomer with a large Stokes radius in solution, binds HGF͞SF in the absence or presence of heparin, and forms a stable HGF͞SF-heparin-MET complex with 1:1:1 stoichiometry. We also show that the ligand-binding domain adopts a ␤-propeller fold, which is similar to the N-terminal domain of ␣V integrin, and that the C-terminal half contains four Ig domains (amino acids 563-654, 657-738, 742-836, and 839 -924) of the unusual structural E set, which could be modeled on bacterial enzymes. Our studies provide 3D models and a functional map of the MET ectodomain. They have broad implications for structurefunction of the MET receptor and the related semaphorin and plexin proteins.Ig domain ͉ sema domain ͉ integrin ␣-chain ͉ hidden Markov models ͉ semaphorins R eceptor tyrosine kinases (RTKs) mediate intercellular signals, which are essential for the development and maintenance of the cells of multicellular organisms. The minimal domain structure of RTKs consists of an extracellular ligandbinding domain, a single transmembrane helix, and a cytoplasmic kinase domain. This minimal structure, however, is very rare, and, typically, the extracellular moiety of RTKs, the ectodomain, consists of complex and distinctive domain sets, which enable classification of the RTKs in different families (1).There is a strong preference for certain domains to occur in the ectodomain of RTKs. The fibronectin type-3 (FN-3) domain, for example, is present as two copies in the large Eph receptor family, three copies in the insulin and IGF-1 receptors, and at least seven copies in the rod outer segment receptor (1). Cystine-rich domains of variable length are also commonly found in RTKs.A large number of RTKs contain Ig domains and the ectodomain of certain families consists solely of Ig domains: the fibroblast growth factor (FGF) receptors contain two or three, depending on RNA splicing, the platelet-derived growth factor (PDGF), colony-stimulating factor 1 (CSF1), KIT, and FLT kinase͞serine-threonine kinase 1 (FLK2͞STK1) receptors contain five, and the FMS-like (FLT1), FLK1, FLT4, and cholecystokinin 4 (CCK4) receptors contain seven (1). Ig domains can also be present in combination with FN-3, cystine-rich, or other domains (1). Interestingly, most Ig domains present in RTKs and cell adhesion molecules belong to a distinct structural set known as the I set, with architecture intermediate between the V and C1 sets (2).MET, the RTK encoded by the c-met protoon...

Objective Abscisic acid (ABA) is a plant hormone also present and active in animals. In mammals, ABA regulates blood glucose levels by stimulating insulin-independent glucose uptake and metabolism in adipocytes and myocytes through its receptor LANCL2. The objective of this study was to investigate whether another member of the LANCL protein family, LANCL1, also behaves as an ABA receptor and, if so, which functional effects are mediated by LANCL1. Methods ABA binding to human recombinant LANCL1 was explored by equilibrium-binding experiments with [ 3 H]ABA, circular dichroism, and surface plasmon resonance. Rat L6 myoblasts overexpressing either LANCL1 or LANCL2, or silenced for the expression of both proteins, were used to investigate the basal and ABA-stimulated transport of a fluorescent glucose analog (NBDG) and the signaling pathway downstream of the LANCL proteins using Western blot and qPCR analysis. Finally, glucose tolerance and sensitivity to ABA were compared in LANCL2 −/− and wild-type (WT) siblings. Results Human recombinant LANCL1 binds ABA with a K d between 1 and 10 μM, depending on the assay (i.e., in a concentration range that lies between the low and high-affinity ABA binding sites of LANCL2). In L6 myoblasts, LANCL1 and LANCL2 similarly, i) stimulate both basal and ABA-triggered NBDG uptake (4-fold), ii) activate the transcription and protein expression of the glucose transporters GLUT4 and GLUT1 (4-6-fold) and the signaling proteins AMPK/PGC-1α/Sirt1 (2-fold), iii) stimulate mitochondrial respiration (5-fold) and the expression of the skeletal muscle (SM) uncoupling proteins sarcolipin (3-fold) and UCP3 (12-fold). LANCL2 −/− mice have a reduced glucose tolerance compared to WT. They spontaneously overexpress LANCL1 in the SM and respond to chronic ABA treatment (1 μg/kg body weight/day) with an improved glycemia response to glucose load and an increased SM transcription of GLUT4 and GLUT1 (20-fold) of the AMPK/PGC-1α/Sirt1 pathway and sarcolipin, UCP3, and NAMPT (4- to 6-fold). Conclusions LANCL1 behaves as an ABA receptor with a somewhat lower affinity for ABA than LANCL2 but with overlapping effector functions: stimulating glucose uptake and the expression of muscle glucose transporters and mitochondrial uncoupling and respiration via the AMPK/PGC-1α/Sirt1 pathway. Receptor redundancy may have been advantageous in animal evolution, given the role of the ABA/LANCL system in the insulin-independent stimulation of cell glucose uptake and energy metabolism.

Auto-antibodies are classically associated with autoimmune diseases, where they are an integral part of diagnostic panels. However, recent evidence is accumulating on the presence of auto-antibodies against single or selected panels of auto-antigens in many types of cancer. Auto-antibodies might initially represent an epiphenomenon derived from the inflammatory environment induced by the tumor. However, their effect on tumor evolution can be crucial, as is discussed in this paper. It has been demonstrated that some of these auto-antibodies can be used for early detection and cancer staging, as well as for monitoring of cancer regression during treatment and follow up. Interestingly, certain auto-antibodies were found to promote cancer progression and metastasis, while others contribute to the body’s defense against it. Moreover, auto-antibodies are of a polyclonal nature, which means that often several antibodies are involved in the response to a single tumor antigen. Dissection of these antibody specificities is now possible, allowing their identification at the genetic, structural, and epitope levels. In this review, we report the evidence available on the presence of auto-antibodies in the main cancer types and discuss some of the open issues that still need to be addressed by the research community.