title: Murine erythroleukemia cells possess an active ubiquitin- and ATP-dependent proteolytic pathway.
abstract: The ubiquitin (Ub)-dependent proteolytic pathway may function in selective elimination of cellular proteins during erythroid differentiation. Murine erythroleukemia (MEL) cells, which can be induced to differentiate to reticulocytes in culture, may provide a convenient system for studying the role of Ub-dependent proteolysis in erythroid differentiation. The following observations indicate that MEL cells possess an active Ub-dependent proteolytic pathway. (i) Addition of purified Ub to MEL cell fraction II (Ub-depleted lysate) stimulated ATP-dependent degradation of radioiodinated proteins. (ii) Covalent conjugation of carboxyl termini of Ub molecules to substrate protein amino groups is a necessary step in Ub-dependent degradation. Des-glygly-Ub (Ub lacking its carboxyl-terminal glygly moiety) did not stimulate protein degradation in MEL cell fraction II. (iii) The Ub-dependent component of protein degradation in MEL cell fraction II was specifically inhibited by amino acid derivatives that are inhibitors of Ub-protein ligase. (iv) MEL cell fraction II contained apparent homologs of all of the rabbit reticulocyte Ub carrier proteins (E2's) except E2(20K) and E2(230K). Ub-dependent proteolysis was seen only in MEL cell lysates prepared in the presence of leupeptin; an enzyme of the proteolytic pathway was inactivated if leupeptin was omitted.
authors.affiliation: Department of Biochemistry, State University of New York, Buffalo 14214.
authors.forename: C M
authors.initials: CM
authors.lastname: Pickart
authors.forename: L A
authors.initials: LA
authors.lastname: Graziani
authors.forename: S F
authors.initials: SF
authors.lastname: Dosch
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D002454:Cell Differentiation; D007782:Lactoglobulins / Q000378:metabolism; D004915:Leukemia, Erythroblastic, Acute / Q000201:enzymology*; D007976:Leupeptins / Q000494:pharmacology; D008025:Ligases / Q000097:blood; D008247:Lysosomes / Q000201:enzymology; D051379:Mice; D010447:Peptide Hydrolases / Q000097:blood*; D011480:Protease Inhibitors / Q000494:pharmacology; D012156:Reticulocytes / Q000201:enzymology; D014407:Tumor Cells, Cultured; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000494:pharmacology*
chemical_list: D007782:Lactoglobulins; D007976:Leupeptins; D011480:Protease Inhibitors; D014452:Ubiquitins; D000255:Adenosine Triphosphate; D044767:Ubiquitin-Protein Ligases; D010447:Peptide Hydrolases; D008025:Ligases; C032854:leupeptin