title: The suppressor domain of inositol 1,4,5-trisphosphate receptor plays an essential role in the protection against apoptosis.
abstract: The N-terminal 1-225 amino acids (aa) of the type 1 inositol 1,4,5-trisphosphate receptor (IP(3)R1) function as a suppressor/coupling domain. In this study we used IP(3)R-deficient B-lymphocytes to investigate the effects of modifications in this domain on IP(3) binding and Ca(2+)-release activity. Although the N-terminal 1-225 aa of IP(3)R3 had the same role as in IP(3)R1, the suppression of IP(3) binding for IP(3)R1 was lost when the suppressor/coupling domains were exchanged between the two isoforms. Resulting chimeric receptors showed a higher sensitivity to IP(3)-induced activation (IICR). Deletion of 11 aa in IP(3)R1 ([Delta76-86]-IP(3)R1) or replacing aa 76-86 of the IP(3)R1 in the suppressor/coupling domain by 13 aa of IP(3)R3 ([75-87 T3]-IP(3)R1) also resulted in increased IP(3) binding and sensitivity of IICR. These residues constitute the only part of the suppressor/coupling domain that is strikingly different between the two isoforms. Expression of [Delta76-86]-IP(3)R1 and of [75-87 T3]-IP(3)R1 increased the propensity of cells to undergo staurosporine-induced apoptosis, but had no effect on the Ca(2+) content in the endoplasmic reticulum. In the cell model used, our observations suggest that the sensitivity of the Ca(2+)-release activity of IP(3)R1 to IP(3) influences the sensitivity of the cells to apoptotic stimuli and that the suppressor/coupling domain may have an anti-apoptotic function by attenuating the sensitivity of IICR.
authors.affiliation: Laboratorium voor Fysiologie, KU Leuven Campus Gasthuisberg O/N, Belgium.
authors.forename: Karolina
authors.initials: K
authors.lastname: Szlufcik
authors.forename: Geert
authors.initials: G
authors.lastname: Bultynck
authors.forename: Geert
authors.initials: G
authors.lastname: Callewaert
authors.forename: Ludwig
authors.initials: L
authors.lastname: Missiaen
authors.forename: Jan B
authors.initials: JB
authors.lastname: Parys
authors.forename: Humbert
authors.initials: H
authors.lastname: De Smedt
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001665:Binding Sites / Q000502:physiology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D015220:Calcium Channels / Q000235:genetics / Q000502:physiology*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002645:Chickens; D017124:Conserved Sequence; D016153:Genes, Suppressor / Q000502:physiology; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D053496:Inositol 1,4,5-Trisphosphate Receptors; D008969:Molecular Sequence Data; D017434:Protein Structure, Tertiary / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000502:physiology*; D017386:Sequence Homology, Amino Acid
chemical_list: D015220:Calcium Channels; C506926:ITPR1 protein, human; D053496:Inositol 1,4,5-Trisphosphate Receptors; D018160:Receptors, Cytoplasmic and Nuclear; D015544:Inositol 1,4,5-Trisphosphate; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases; D002118:Calcium