title: Ectodomain shedding, translocation and synthesis of SorLA are stimulated by its ligand head activator.
abstract: The single transmembrane receptor SorLA is the mammalian orthologue of the head activator-binding protein, HAB, from hydra. The human neuronal precursor cell line NT2 and the neuroendocrine cell line BON produce head activator (HA) and respond to HA by entry into mitosis and cell proliferation. They express SorLA, and bind HA with nanomolar affinity. HA coupled to Sepharose is able to precipitate SorLA specifically proving that SorLA binds HA. Using antisera directed against extra- and intracellular epitopes we find SorLA as membrane receptor and as soluble protein released from cells into the culture medium. Cell lines differ strongly in processing of SorLA, with NT2 cells expressing SorLA mainly as membrane receptor, whereas release predominates in BON cells. Soluble SorLA lacks the intracellular domain and is shed from the transmembrane protein by a metalloprotease. Release from cells and brain slices is stimulated by HA and by phorbol ester, and it is blocked by a metalloprotease inhibitor and by lowering the temperature to 20 degrees C. Blockade of SorLA shedding and treatment of cells with SorLA antisense oligonucleotides lead to a decrease in the rate of cell proliferation. From this we conclude that SorLA is necessary to mediate the mitogenic effect of endogenous HA. HA enhances the translocation of SorLA from internal membranes to the cell surface and its internalization. In addition, HA stimulates SorLA synthesis hinting at an autocatalytic feedback loop in which the ligand activates production, processing, and translocation of its receptor.
authors.affiliation: Zentrum für Molekulare Neurobiologie, Universität Hamburg, Martinistr. 52, D-20246 Hamburg, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Hampe
authors.forename: I B
authors.initials: IB
authors.lastname: Riedel
authors.forename: J
authors.initials: J
authors.lastname: Lintzel
authors.forename: C O
authors.initials: CO
authors.lastname: Bader
authors.forename: I
authors.initials: I
authors.lastname: Franke
authors.forename: H C
authors.initials: HC
authors.lastname: Schaller
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism / Q000473:pathology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D045683:Furin; D006801:Humans; D026502:LDL-Receptor Related Proteins; D008024:Ligands; D026901:Membrane Transport Proteins; D008666:Metalloendopeptidases / Q000378:metabolism; D051379:Mice; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D009479:Neuropeptides / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D011761:Pyrrolidonecarboxylic Acid / Q000031:analogs & derivatives; D011973:Receptors, LDL / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D012995:Solubility; D013381:Subtilisins / Q000378:metabolism
chemical_list: D026502:LDL-Receptor Related Proteins; D008024:Ligands; D026901:Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D009479:Neuropeptides; D011973:Receptors, LDL; C102582:SORL1 protein, human; C491168:Sorl1 protein, mouse; C032522:head activator peptide; D013381:Subtilisins; D045683:Furin; D008666:Metalloendopeptidases; D011761:Pyrrolidonecarboxylic Acid