title: Positive regulation of mu-calpain action by polyphosphoinositides.
abstract: Whether calcium is the only major intracellular activator of calpain has not yet been established. Here we demonstrate that polyphosphoinositides may play critical roles in the activation process of mu-calpain. Experiments with purified enzyme, substrate (fodrin), and phospholipids show that only polyphosphoinositides but not other lipids significantly promote calpain action in the physiological intracellular calcium range of 10(-7) to 10(-6) M. The effect of polyphosphoinositide is exerted through both a reduction in the calcium concentration required for calpain autolysis and an increase in the Vmax of the proteolytic reaction. Neomycin, a polyphosphoinositide-binding antibiotic, inhibits both polyphosphoinositide-assisted proteolysis in test tubes and calcium-induced calpain activation coupled with substrate proteolysis in intact cells. This implies that the presence of polyphosphoinositides may actually be a prerequisite for calpain activation inside cells.
authors.affiliation: Department of Molecular Biology, Tokyo Metropolitan Institute of Medical Science, Japan.
authors.forename: T C
authors.initials: TC
authors.lastname: Saido
authors.forename: M
authors.initials: M
authors.lastname: Shibata
authors.forename: T
authors.initials: T
authors.lastname: Takenawa
authors.forename: H
authors.initials: H
authors.lastname: Murofushi
authors.forename: K
authors.initials: K
authors.lastname: Suzuki
mesh_terms: D000595:Amino Acid Sequence; D000906:Antibodies; D002118:Calcium / Q000378:metabolism*; D002154:Calpain / Q000378:metabolism*; D002352:Carrier Proteins / Q000302:isolation & purification / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism; D007700:Kinetics; D015458:Leukemia, T-Cell; D046911:Macromolecular Substances; D008565:Membrane Proteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D009355:Neomycin / Q000494:pharmacology; D010455:Peptides / Q000138:chemical synthesis / Q000276:immunology; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols / Q000494:pharmacology*; D010743:Phospholipids / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D013049:Spectrin
chemical_list: D000906:Antibodies; D002118:Calcium; D002154:Calpain; D002352:Carrier Proteins; D007527:Isoenzymes; D046911:Macromolecular Substances; D008565:Membrane Proteins; D008840:Microfilament Proteins; D009355:Neomycin; D010455:Peptides; D019269:Phosphatidylinositol 4,5-Diphosphate; D018129:Phosphatidylinositol Phosphates; D010716:Phosphatidylinositols; D010743:Phospholipids; D013049:Spectrin