Specific regulation of protein phosphatase 2A PR72/B'' subunits by calpain.
Protein phosphatase 2A (PP2A) represents a family of multimeric serine/threonine phosphatases with pleiotropic roles in signal transduction. We previously described the functional analysis of two Ca(2+)-binding EF-hands in the PR72/B'' class of regulatory PP2A subunits. Now we report partial degradation of PR72/B"alpha2 and PR130/B"alpha1 into a 45-48kDa proteolysis-resistant fragment ('PR45') by the Ca(2+)-dependent protease m-calpain. This limited proteolysis is dependent on EF-hand integrity, independent of two PEST-domains, and highly specific as PP2A(C), PR65/A and representatives of PR55/B and PR61/B' subunit families are calpain-resistant. PR45 was also generated in staurosporine-induced apoptotic MCF7 cells in a calpain-dependent way. Calpain treatment weakens the PR72-core enzyme interaction, activates basal PP2A(T72) phosphatase activity and dramatically increases its sensitivity for and activation by polycations. This unique property can be exploited in a specific biochemical assay for these holoenzymes. We propose local calpain action in vivo may constitute a novel regulatory mechanism of these holoenzymes.
Janssens
Veerle
V
Protein Phosphorylation and Proteomics Lab., Dept. of Molecular Cell Biology, Faculty of Medicine, KU Leuven, Gasthuisberg O&N1, Herestraat 49 Box 901, B-3000 Leuven, Belgium. veerle.janssens@med.kuleuven.be
Derua
Rita
R
Zwaenepoel
Karen
K
Waelkens
Etienne
E
Goris
Jozef
J
D000818:Animals; D002154:Calpain / Q000378:metabolism*; D002460:Cell Line; D006801:Humans; D009154:Mutation; D054648:Protein Phosphatase 2 / Q000235:genetics / Q000378:metabolism*; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D011817:Rabbits
D021122:Protein Subunits; D054648:Protein Phosphatase 2; D002154:Calpain; C449000:m-calpain