Neuregulin isoforms in dorsal root ganglion neurons: effects of the cytoplasmic domain on localization and membrane shedding of Nrg-1 type I.
Embryonic sensory neurons express membrane-anchored growth factors that stimulate proliferation and differentiation of Schwann cells. The most important of these are members of the neuregulin-1 (Nrg-1) family that activate the erbB2/erbB3 receptor kinase on Schwann cells. Nrg-1 growth factors display a complex pattern of alternative mRNA splicing. We investigated the expression of the Nrg-1 type I in rat embryo dorsal root ganglion (DRG) neurons. Nrg-1 type I mRNA was abundantly expressed in DRG neurons; molecular cloning identified three distinct isoforms. The most prominent structural difference produced by alternative splicing was truncation of the C-terminal cytoplasmic domain. In sensory neurons and other cells, Nrg-1 type I proteins with the full-length 374-amino-acid cytoplasmic domain were expressed on the cell surface. In contrast, an isoform with a partially truncated cytoplasmic domain was retained in an intracellular compartment. Deletion studies demonstrated the presence of a cryptic intracellular retention signal that was exposed in the truncated cytoplasmic domain. Cell surface Nrg-1 type I molecules were subject to protease-dependent release of the biologically active ectodomain. As a consequence of their intracellular localization, the Nrg-1 type I isoform with a truncated cytoplasmic domain was not subject to membrane shedding. Nrg-1 type I ectodomain release was accelerated by factors present in Schwann cell-conditioned medium. In cells with active Nrg-1 type I ectodomain, shedding products corresponding to the cytoplasmic domain were not detected, because of rapid gamma-secretase- and proteasome-dependent degradation. These results demonstrate that sensory neurons express alternatively spliced neuregulin polypeptides with distinct subcellular localizations and processing.
Zhang
Zhiyou
Z
Weis Center for Research, Geisinger Clinic, Danville, Pennsylvania 17822-02601, USA.
Prentiss
Lisa
L
Heitzman
Deborah
D
Stahl
Richard C
RC
DiPino
Frank
F
Carey
David J
DJ
D000818:Animals; D000831:Animals, Newborn; D020126:Brefeldin A / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D003593:Cytoplasm / Q000187:drug effects / Q000378:metabolism*; D004622:Embryo, Mammalian; D005727:Ganglia, Spinal / Q000166:cytology*; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D020890:Neuregulin-1 / Q000235:genetics / Q000378:metabolism*; D009474:Neurons / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D010649:Phenylalanine / Q000031:analogs & derivatives / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D013876:Thiophenes / Q000494:pharmacology; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection / Q000379:methods
D020890:Neuregulin-1; D011480:Protease Inhibitors; D020033:Protein Isoforms; D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D013876:Thiophenes; D020126:Brefeldin A; D010649:Phenylalanine; C080985:batimastat