CALPAINS AND CALPASTATIN IN SH-SY5Y NEUROBLASTOMA-CELLS DURING RETINOIC ACID-INDUCED DIFFERENTIATION AND NEURITE OUTGROWTH - COMPARISON WITH THE HUMAN BRAIN CALPAIN SYSTEM

Calpains have importance in human neurodegenerative disease pathogenes is, but these mechanisms are difficult to study in postmortem tissues, To establish a cellular model of the human calpain and calpastatin sy stem, we characterized calpain I, calpain II, and calpastatin in SH-SY 5Y human neuroblastoma cells in relation to their counterparts in huma n brain and investigated their expression and activity after inducing cellular differentiation with retinoic acid (RA), a physiological effe ctor of normal brain development, Calpain I in both SH-SY5Y cells and human brain existed in the cytosolic and particulate fractions as thre e isoforms (80, 78, and 76 kDa) and exhibited atypical isoelectric foc using behavior, Calpain II in SH-SY5Y cells, as in human brain, migrat ed as a single predominantly cytosolic 76-kDa protein with an isoelect ric point ranging from 5.9 to 6.3, Calpastatin from both sources was a lso 90% cytosolic, In the cells it was composed of four discrete bands , ranging in molecular weight from 110 to 127 kDa, Levels of activated (76 and 78 kDa) and precursor (80 kDa) calpain I isoforms rose 54% (P < 0.0001) in the particulate fraction and 26% (P < 0.0001) in the sol uble fraction after 3 days of RA exposure, Because levels and activity of calpastatin remain unchanged during the first 7 days of RA exposur e, the increased abundance of calpain I implies a net activation of th e calpain system during differentiation. Calpain I activation may cont ribute to the remodeling of cell shape and neurite extension/retractio n associated with neuronal differentiation. (C) 1997 Wiley-Liss, Inc.