title: 2-Aminoethoxydiphenyl borate inhibits inositol 1,4,5-trisphosphate receptor function, ubiquitination and downregulation, but acts with variable characteristics in different cell types.
abstract: 2-Aminoethoxydiphenyl borate (2-APB) is a putative, membrane-permeable inhibitor of inositol 1,4,5-trisphosphate (InsP(3)) receptors, but it is the case that little is known about its action at the InsP(3) receptor level. Thus, we examined the effects of 2-APB on InsP(3) receptor-mediated effects in a range of cell types expressing different complements of InsP(3) receptor types. In experiments with permeabilized cells we found that 2-APB could inhibit InsP(3)-induced release of stored Ca(2+), but also that it released Ca(2+), and that the prevalence of these two effects varied between different cell types and did not correlate with the expression of a particular receptor type. These effects of 2-APB reflected an interaction distal to the ligand binding site of InsP(3) receptors, since InsP(3) binding was unaffected by 2-APB. In intact cells, we found only inhibitory effects of 2-APB on Ca(2+) mobilization, and that variation between cell types in the characteristics of this inhibition appeared to be due to differential entry of 2-APB. 2-APB also inhibited InsP(3) receptor ubiquitination and proteasomal degradation, which again was cell type dependent. In total, these data reveal a remarkable degree of variation between cell types in the effects of 2-APB, showing that its usefulness as a specific and universal inhibitor of InsP(3) receptors is limited. However, the ability of 2-APB to inhibit InsP(3) receptor ubiquitination and degradation indicates that 2-APB may block InsP(3)-induced conformational changes in the receptor, resulting in perturbation of multiple regulatory events.
authors.affiliation: Department of Pharmacology, SUNY Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210-2339, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Soulsby
authors.forename: R J H
authors.initials: RJ
authors.lastname: Wojcikiewicz
mesh_terms: D000818:Animals; D001896:Boron Compounds / Q000494:pharmacology*; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000187:drug effects* / Q000378:metabolism; D006224:Cricetinae; D015536:Down-Regulation / Q000502:physiology*; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D001896:Boron Compounds; D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D025801:Ubiquitin; D015544:Inositol 1,4,5-Trisphosphate; C109986:2-aminoethoxydiphenyl borate; D002118:Calcium