title: Chymotrypsin B cached in rat liver lysosomes and involved in apoptotic regulation through a mitochondrial pathway.
abstract: Lysosomes can trigger the mitochondrial apoptotic pathway by releasing proteases. Here we report that a 25-kDa protein purified from rat liver lysosomes possesses a long standing potent Bid cleavage activity at neutral pH, and the truncated Bid can in turn induce rapid mitochondrial release of cytochrome c. This protease was revealed as chymotrypsin B by biochemical and mass spectrometric analysis. Although it was long recognized as a digestive protease exclusively secreted by the exocrine pancreas, our data support that it also expresses and intracellularly resides in rat liver lysosomes. Translocation of lysosomal chymotrypsin B into cytosol was triggered by apoptotic stimuli such as tumor necrosis factor-alpha, and intracellular delivery of chymotrypsin B protein induced apoptotic cell death with a potency comparable with cathepsin B, suggestive of a lysosomal-mitochondrial pathway to apoptosis regulated by chymotrypsin B following its release. Noteworthily, either knockdown of chymotrypsin B expression by RNA interference or pretreatment with chymotrypsin B inhibitor N-p-tosyl-L-phenylalanine chloromethyl ketone significantly reduced tumor necrosis factor-alpha-induce apoptosis. These results demonstrate for the first time that chymotrypsin B is not only restricted to the pancreas but can function intracellularly as a pro-apoptotic protease.
authors.affiliation: National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, Chaoyang District, Beijing, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Miao
authors.forename: Yang
authors.initials: Y
authors.lastname: Sun
authors.forename: Taotao
authors.initials: T
authors.lastname: Wei
authors.forename: Xingyu
authors.initials: X
authors.lastname: Zhao
authors.forename: Kai
authors.initials: K
authors.lastname: Zhao
authors.forename: Ling
authors.initials: L
authors.lastname: Yan
authors.forename: Xujia
authors.initials: X
authors.lastname: Zhang
authors.forename: Hongjun
authors.initials: H
authors.lastname: Shu
authors.forename: Fuyu
authors.initials: F
authors.lastname: Yang
mesh_terms: D000818:Animals; D017209:Apoptosis; D002460:Cell Line; D002918:Chymotrypsin / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D022781:Hepatocytes / Q000201:enzymology; D008099:Liver / Q000201:enzymology*; D008247:Lysosomes / Q000201:enzymology*; D008928:Mitochondria / Q000201:enzymology*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction
chemical_list: D012333:RNA, Messenger; D002918:Chymotrypsin; C117609:chymotrypsin B