Changes in intracellular calpastatin localization are mediated by reversible phosphorylation.
We have previously reported that, in neuroblastoma LAN-5 cells, calpastatin is in an aggregated state, close to the cell nucleus [de Tullio, Passalacqua, Averna, Salamino, Melloni and Pontremoli (1999) Biochem. J. 343, 467-472]. In the present paper, we demonstrate that aggregated calpastatin is predominantly in a phosphorylated state. An increase in intracellular free [Ca2+] induces both dephosphorylation of calpastatin, through the action of a phosphoprotein phosphatase, and its redistribution as a soluble inhibitor species. cAMP, but not PMA-induced phosphorylation, reverses calpastatin distribution favouring its aggregation. This intracellular reversible mechanism, regulating the level of cytosolic calpastatin, could be considered a strategy through which calpain can escape calpastatin inhibition, especially during earlier steps of its activation process.
Averna
M
M
Department of Experimental Medicine, Biochemistry Section, University of Genoa, Viale Benedetto XV 1, 16132 Genoa, Italy.
de Tullio
R
R
Passalacqua
M
M
Salamino
F
F
Pontremoli
S
S
Melloni
E
E
D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002852:Chromatography, Ion Exchange; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D006801:Humans; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D014407:Tumor Cells, Cultured
D002135:Calcium-Binding Proteins; C033668:calpastatin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C