title: Shedding and gamma-secretase-mediated intramembrane proteolysis of the mucin-type molecule CD43.
abstract: CD43 is a transmembrane molecule that contains a 123-aminoacids-long cytoplasmic tail and a highly O-glycosylated extracellular domain of mucin type. Endogenous CD43 expressed in COLO 205, K562 and Jurkat cells revealed a membrane-associated, 20 kDa CD43-specific cytoplasmic tail fragment (CD43-CTF) upon inhibition of gamma-secretase. This fragment was formed by an extracellular cleavage, as it was not accumulated after treating cells with 1,10-phenanthroline, a metalloprotease inhibitor. When CD43 was transfected into HEK-293 cells expressing dominant-negative PS1 (presenilin-1), the CD43-CTF was accumulated, but not in cells with wild-type PS1. Owing to its accumulation in the presence of a non-functional PS variant, it may thus be a novel gamma-secretase substrate. This CTF is formed by an extracellular cleavage close to the membrane, is a fragment that can be concluded to be a substrate for gamma-secretase. However, the intracellular gamma-secretase product has not been possible to detect, suggesting a quick processing of this product. During normal growth the CTF was not found without gamma-secretase inhibition, but when the cells (COLO 205) were very confluent the fragment could be detected. The intracellular domain of CD43 has previously been shown to contain a functional nuclear localization signal, and has been suggested to be involved in gene activation. From this and the present results, a novel way to explain how mucin-type molecules may transduce intracellular signals can be proposed.
authors.affiliation: Department of Medical Biochemistry, Göteborg University, Medicinaregatan 9A, 413 90 Gothenburg, Sweden.
authors.forename: Christian X
authors.initials: CX
authors.lastname: Andersson
authors.forename: Julia
authors.initials: J
authors.lastname: Fernandez-Rodriguez
authors.forename: Sirle
authors.initials: S
authors.lastname: Laos
authors.forename: Dan
authors.initials: D
authors.lastname: Baeckström
authors.forename: Christian
authors.initials: C
authors.lastname: Haass
authors.forename: Gunnar C
authors.initials: GC
authors.lastname: Hansson
mesh_terms: D053829:Amyloid Precursor Protein Secretases; D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D016282:Aspartic Acid Endopeptidases / Q000378:metabolism*; D002460:Cell Line; D010450:Endopeptidases; D015870:Gene Expression; D006801:Humans; D051917:Leukosialin; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D010957:Plasmids; D053764:Presenilin-1; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins; D012795:Sialoglycoproteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D015703:Antigens, CD; D051917:Leukosialin; D008565:Membrane Proteins; C508853:PSEN1 protein, human; D053764:Presenilin-1; D011994:Recombinant Proteins; C465014:SPN protein, human; D012795:Sialoglycoproteins; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human