title: Enzymatic cleavage as a processing step in the maturation of Muc4/sialomucin complex.
abstract: Cleavage of Muc4/SMC precursor into two subunits is an essential processing step for maturation and occurs within a GD-PH sequence. Recent evidence indicates that cleavage of the precursor of gel-forming mucin MUC2 within the same tetrapeptide sequence occurs by a non-enzymatic, autocatalytic cleavage at low pH, and in cells in the late secretory pathway. Here we provide evidence that the cleavage step of Muc4/SMC processing occurs by a proteolytic mechanism. First, processing of Muc4/SMC precursor to ASGP-2 was inhibited in the presence of the mechanism-based serine protease inhibitor, Pefabloc SC, under conditions that did not block synthesis of other proteins. This inhibition led to an increased level of the precursor. Second, neutralization of the acidic environment of the late secretory pathway with NH4Cl did not inhibit cleavage of Muc4/SMC precursor. These results indicate that the two mucins can be processed by cleavage at the same peptide site by different mechanisms.
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Miami School of Medicine, Miami, Florida 33101, USA.
authors.forename: Pedro
authors.initials: P
authors.lastname: Soto
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.forename: Kermit L
authors.initials: KL
authors.lastname: Carraway
mesh_terms: D000643:Ammonium Chloride / Q000378:metabolism / Q000494:pharmacology; D002460:Cell Line; D004305:Dose-Response Relationship, Drug; D006031:Glycosylation; D006801:Humans; D006863:Hydrogen-Ion Concentration; D055262:Mucin-2; D055264:Mucin-4; D009077:Mucins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D011480:Protease Inhibitors / Q000378:metabolism / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D012795:Sialoglycoproteins / Q000378:metabolism; D013450:Sulfones / Q000378:metabolism / Q000494:pharmacology; D014162:Transfection
chemical_list: C524625:MUC2 protein, human; C524658:MUC4 protein, human; D055262:Mucin-2; D055264:Mucin-4; D009077:Mucins; D011480:Protease Inhibitors; D012795:Sialoglycoproteins; D013450:Sulfones; D000643:Ammonium Chloride; C002010:4-(2-aminoethyl)benzenesulfonylfluoride; D010447:Peptide Hydrolases