Functional characterization of the P1059L mutation in the inositol 1,4,5-trisphosphate receptor type 1 identified in a Japanese SCA15 family Haruka Yamazaki a , Hiroaki Nozaki b , Osamu Onodera c , Takayuki Michikawa a,1 , Masatoyo Nishizawa b , Katsuhiko Mikoshiba a,⇑ a Laboratory for Developmental Neurobiology, RIKEN Brain Science Institute, Saitama 351-0198, Japan b Department of Neurology, Clinical Neuroscience Branch, Brain Research Institute, Niigata University, Niigata 951-8585, Japan c Department of Molecular Neuroscience, Resource Branch for Brain Disease Research, Center for Bioresource-based Research, Brain Research Institute, Niigata University, Niigata 951-8585, Japan article info Article history: Received 2 June 2011 Available online 13 June 2011 Keywords: Calcium channel Inositol 1,4,5-trisphosphate Inositol 1,4,5-trisphosphate receptor Neurodegenerative disorder SCA15 Spinocerebellar ataxia abstract Spinocerebellar ataxia type 15 (SCA15) is a group of human neurodegenerative disorders characterized by a slowly progressing pure cerebellar ataxia. The inositol 1,4,5-trisphosphate (IP 3 ) receptor type 1 (IP 3 R1) is an intracellular IP 3 -induced Ca 2+ release channel that was recently identified as a causative gene for SCA15. In most case studies, a heterozygous deletion of the IP 3 R1 gene was identified. However, one Jap- anese SCA15 family was found to have a Pro to Leu (P1059L) substitution in IP 3 R1. To investigate the effect of the P1059L mutation, we analyzed the channel properties of the mutant human IP 3 R1 by expressing it in an IP 3 R-deficient B lymphocyte cell line. The P1059L mutant was a functional Ca 2+ release channel with a twofold higher IP 3 binding affinity compared to wild-type IP 3 R1. The cooperative depen- dence of the Ca 2+ release activity of the mutant on IP 3 concentration was reduced, but both wild-type and mutant receptors produced similar B cell receptor-induced Ca 2+ signals. These results demonstrate that the Ca 2+ release properties of IP 3 R1 are largely unaffected by the P1059L mutation. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction Spinocerebellar ataxias (SCAs) comprise a heterogeneous group of dominantly inherited neurodegenerative disorders that are clin- ically and genetically classified into more than 30 subtypes [1]. SCA type 15 (SCA15) is characterized by a pure cerebellar ataxia, very slow progression, and marked cerebellar atrophy [2,3]. Recently, the inositol 1,4,5-trisphosphate (IP 3 ) receptor type 1 (IP 3 R1) was identified as a causative gene for SCA15 [4,5], and SCA16 was reas- signed to the SCA15 group because the IP 3 R1 deletion was con- firmed in SCA16 patients [6]. To date, about 10 SCA15 kindreds have been identified, and most have heterozygous deletions at the 5 0 end of the IP 3 R1 gene, with or without additional deletions of the adjacent gene encoding sulfatase modifying factor 1 [7,8]. SCA15 patients with heterozygous deletions of the IP 3 R1 gene have a dramatic decrease in IP 3 R1 expression levels [4,5,7]. Only one Japanese SCA15 family was found to have a heterozygous substitu- tion of Pro to Leu at position 1059 (P1059L) in IP 3 R1 [4]. IP 3 Rs function as IP 3 -induced Ca 2+ release channels and are localized to the membranes of intracellular Ca 2+ stores such as the endoplasmic reticulum [9,10]. In mammals, there are three IP 3 R isoforms [11] and IP 3 R1 is the major isoform in the central nervous system, especially enriched in cerebellar Purkinje cells [12]. Crucial roles for IP 3 R1 have been reported in synaptic plastic- ity [13,14], dendritic morphology [15], and growth cone navigation [16,17]. Most IP 3 R1 knockout mice die in utero, and newborn ani- mals begin to show severe ataxia at approximately postnatal day 9 (P9) and die by the weaning period [18]. Two lines of spontane- ous IP 3 R1 mutant mice, opisthotonos (opt) [19] and D18 [5] mice, have homozygous in-frame deletions of IP 3 R1 (Fig. 1). Both mutant strains show a marked decrease in IP 3 R1 protein levels and present an ataxic phenotype around P14 and die by one month. The domain structure of IP 3 R has been well characterized in mouse IP 3 R1 [20,21] (Fig. 1), which has 99% amino acid sequence identity with that of human IP 3 R1 [22]. IP 3 R is a tetrameric channel [23] and IP 3 binds to the IP 3 -binding core domain [24–26] of each IP 3 R1 subunit to release Ca 2+ through the channel pore that is esti- mated to be formed by tetrameric transmembrane domains [27]. The P1059L mutation site of human IP 3 R1 corresponds to the Pro-1073 residue of mouse IP 3 R1 and is localized to the regula- tory/coupling domain that connects the IP 3 -binding core and trans- membrane domains (Fig. 1). We report here the effect of the P1059L mutation on the channel properties of human IP 3 R1. 0006-291X/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.bbrc.2011.06.043 ⇑ Corresponding author. Address: Laboratory for Developmental Neurobiology, RIKEN Brain Science Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan. Fax: +81 48 467 9744. E-mail address: mikosiba@brain.riken.jp (K. Mikoshiba). 1 Present address: Laboratory for Molecular Neurogenesis, RIKEN Brain Science Institute, Saitama 351-0198, Japan. Biochemical and Biophysical Research Communications 410 (2011) 754–758 Contents lists available at ScienceDirect Biochemical and Biophysical Research Communications journal homepage: www.elsevier.com/locate/ybbrc