title: The Bcl-2 protein family member Bok binds to the coupling domain of inositol 1,4,5-trisphosphate receptors and protects them from proteolytic cleavage.
abstract: Bok is a member of the Bcl-2 protein family that controls intrinsic apoptosis. Bok is most closely related to the pro-apoptotic proteins Bak and Bax, but in contrast to Bak and Bax, very little is known about its cellular role. Here we report that Bok binds strongly and constitutively to inositol 1,4,5-trisphosphate receptors (IP3Rs), proteins that form tetrameric calcium channels in the endoplasmic reticulum (ER) membrane and govern the release of ER calcium stores. Bok binds most strongly to IP3R1 and IP3R2, and barely to IP3R3, and essentially all cellular Bok is IP3R bound in cells that express substantial amounts of IP3Rs. Binding to IP3Rs appears to be mediated by the putative BH4 domain of Bok and the docking site localizes to a small region within the coupling domain of IP3Rs (amino acids 1895-1903 of IP3R1) that is adjacent to numerous regulatory sites, including sites for proteolysis. With regard to the possible role of Bok-IP3R binding, the following was observed: (i) Bok does not appear to control the ability of IP3Rs to release ER calcium stores, (ii) Bok regulates IP3R expression, (iii) persistent activation of inositol 1,4,5-trisphosphate-dependent cell signaling causes Bok degradation by the ubiquitin-proteasome pathway, in a manner that parallels IP3R degradation, and (iv) Bok protects IP3Rs from proteolysis, either by chymotrypsin in vitro or by caspase-3 in vivo during apoptosis. Overall, these data show that Bok binds strongly and constitutively to IP3Rs and that the most significant consequence of this binding appears to be protection of IP3Rs from proteolysis. Thus, Bok may govern IP3R cleavage and activity during apoptosis.
authors.affiliation: From the Department of Pharmacology, SUNY Upstate Medical University, Syracuse, New York 13210 and.
authors.forename: Jacqualyn J
authors.initials: JJ
authors.lastname: Schulman
authors.affiliation: From the Department of Pharmacology, SUNY Upstate Medical University, Syracuse, New York 13210 and.
authors.forename: Forrest A
authors.initials: FA
authors.lastname: Wright
authors.affiliation: University of Bern, Medical Faculty, Institute of Pharmacology, Friedbuehlstrasse 49, CH-3010 Bern, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Kaufmann
authors.affiliation: From the Department of Pharmacology, SUNY Upstate Medical University, Syracuse, New York 13210 and. Electronic address: wojcikir@upstate.edu.
authors.forename: Richard J H
authors.initials: RJH
authors.lastname: Wojcikiewicz
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D002118:Calcium / Q000378:metabolism; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D002461:Cell Line, Transformed; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D053496:Inositol 1,4,5-Trisphosphate Receptors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary; D059748:Proteolysis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*
chemical_list: C503049:BOK protein, human; C111858:Bok protein, mouse; D053496:Inositol 1,4,5-Trisphosphate Receptors; D019253:Proto-Oncogene Proteins c-bcl-2; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D002118:Calcium
keywords: Apoptosis; Bcl-2 Family Proteins; Bok; Caspase; Inositol 1,4,5-Trisphosphate; Inositol 1,4,5-Trisphosphate Receptor; Proteolysis; Ubiquitin