title: Cleavage of Bax to p18 Bax accelerates stress-induced apoptosis, and a cathepsin-like protease may rapidly degrade p18 Bax.
abstract: Bax is cleaved by calpain at aspartate 33 (Asp33) to yield p18 Bax during stress-induced apoptosis. To assess the role of p18 Bax in apoptosis, an ecdysone-inducible expression system was generated. Similar levels of wild-type (WT) and noncleavable Asp33Ala (Asp-->Ala) Bax are induced in 293 cells while expression of N-terminal-deleted p18 (Delta1-33) Bax remains low (20% of full-length p21 Bax) due to a reduced half-life (2 hours versus 12 hours for p21 Bax) resulting from increased sensitivity to cathepsin-like proteolytic degradation. Expression of p18 Bax is enhanced to levels comparable to p21 Bax when induction is carried out in the presence of cathepsin inhibitors, Z-Phe-Gly-NHO-Bz or N-Acetyl-Leu-Leu-Met-CHO. Compared with WT Bax, expression of similar levels of p18 Bax and, surprisingly, Asp33Ala Bax more potently induces apoptosis as indicated by increased cytochrome c release, caspase-9/-3 activation, and DNA fragmentation, potentially due to their increased homo-oligomerization in mitochondrial membranes. Studies in A-549, U-937, K-562, and HL-60 cells confirm that inhibition of Bax cleavage results in 25% to 35% reduction of drug-induced apoptosis, while inhibition of p18 Bax degradation enhances apoptosis by 25% to 40%. Results indicate that although cleavage to p18 Bax is not required for Bax to initiate apoptosis, p18 Bax potently accelerates the apoptotic process.
authors.affiliation: University of Florida Shands Cancer Center, UF Shands Cancer Center, Gainesville, USA.
authors.forename: Xuefang
authors.initials: X
authors.lastname: Cao
authors.forename: Xingming
authors.initials: X
authors.lastname: Deng
authors.forename: W Stratford
authors.initials: WS
authors.lastname: May
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002403:Cathepsins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003574:Cytochrome c Group / Q000378:metabolism; D004441:Ecdysterone / Q000031:analogs & derivatives / Q000494:pharmacology; D010450:Endopeptidases / Q000378:metabolism*; D005047:Etoposide / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D018922:HL-60 Cells; D006801:Humans; D007377:Interleukin-3 / Q000494:pharmacology; D020014:K562 Cells; D007668:Kidney / Q000166:cytology; D008175:Lung Neoplasms; D051379:Mice; D008928:Mitochondria / Q000378:metabolism; D016296:Mutagenesis; D010446:Peptide Fragments / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D020298:U937 Cells; D051028:bcl-2-Associated X Protein
chemical_list: D000970:Antineoplastic Agents; C494826:BAX protein, human; C494827:Bax protein, mouse; D003574:Cytochrome c Group; D007377:Interleukin-3; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D004441:Ecdysterone; D005047:Etoposide; C008999:ponasterone A; D002403:Cathepsins; D010450:Endopeptidases; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D002154:Calpain; C505409:Casp3 protein, mouse; C506434:Casp9 protein, mouse; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases