title: PMCA4 (ATP2B4) mutation in familial spastic paraplegia causes delay in intracellular calcium extrusion.
abstract: BACKGROUND
  Familial spastic paraplegia (FSP) is a heterogeneous group of disorders characterized primarily by progressive lower limb spasticity and weakness. More than 50 disease loci have been described with different modes of inheritance. Recently, we described a novel missense mutation (c.803G>A, p.R268Q) in the plasma membrane calcium ATPase (PMCA4, or ATP2B4) gene in a Chinese family with autosomal dominant FSP. Further to this finding, here we describe the functional effect of this mutation.
  
  
  METHODS
  As PMCA4 removes cytosolic calcium, we measured transient changes and the time-dependent decay of cytosolic calcium level as visualized by using fura-2 fluorescent dye with confocal microscopy in human SH-SY5Y neuroblastoma cells overexpressing either wild-type or R268Q mutant PMCA4.
  
  
  RESULTS
  Overexpressing both wild-type and R268Q PMCA4 significantly reduced maximum calcium surge after KCl-induced depolarization as compared with vector control cells. However, cells overexpressing mutant PMCA4 protein demonstrated significantly higher level of calcium surge when compared with wild-type. Furthermore, the steady-state cytosolic calcium concentration in these mutant cells remained markedly higher than the wild-type after SERCA inhibition by thapsigargin.
  
  
  CONCLUSIONS
  Our result showed that p.R268Q mutation in PMCA4 resulted in functional changes in calcium homeostasis in human neuronal cells. This suggests that calcium dysregulation may be associated with the pathogenesis of FSP.
authors: Division of Neurology, Department of Medicine, University of Hong Kong Hong Kong, China ; Research Centre of Heart, Brain, Hormone and Healthy Aging, University of Hong Kong Hong Kong, China.
authors: Philip Wing-Lok
authors: PW
authors: Ho
authors: Division of Neurology, Department of Medicine, University of Hong Kong Hong Kong, China.
authors: Shirley Yin-Yu
authors: SY
authors: Pang
authors: Department of Psychiatry, University of Hong Kong Hong Kong, China ; Centre for Reproduction, Development and Growth, University of Hong Kong Hong Kong, China ; Centre for Genomic Sciences, University of Hong Kong Hong Kong, China.
authors: Miaoxin
authors: M
authors: Li
authors: Division of Neurology, Department of Medicine, University of Hong Kong Hong Kong, China.
authors: Zero Ho-Man
authors: ZH
authors: Tse
authors: Division of Neurology, Department of Medicine, University of Hong Kong Hong Kong, China.
authors: Michelle Hiu-Wai
authors: MH
authors: Kung
authors: Department of Psychiatry, University of Hong Kong Hong Kong, China ; Centre for Reproduction, Development and Growth, University of Hong Kong Hong Kong, China ; Centre for Genomic Sciences, University of Hong Kong Hong Kong, China.
authors: Pak-Chung
authors: PC
authors: Sham
authors: Division of Neurology, Department of Medicine, University of Hong Kong Hong Kong, China.
authors: Shu-Leong
authors: SL
authors: Ho
mesh_terms: D044466:Asian People / Q000235:genetics*; D015153:Blotting, Western; D002118:Calcium / Q000032:analysis; D005456:Fluorescent Dyes; D016257:Fura-2; D006801:Humans; D018613:Microscopy, Confocal / Q000379:methods; D020125:Mutation, Missense; D053499:Plasma Membrane Calcium-Transporting ATPases; D060888:Real-Time Polymerase Chain Reaction; D015419:Spastic Paraplegia, Hereditary / Q000235:genetics*
chemical_list: D005456:Fluorescent Dyes; C507517:ATP2B4 protein, human; D053499:Plasma Membrane Calcium-Transporting ATPases; D002118:Calcium; D016257:Fura-2
keywords: ATP2B4; Familial spastic paraplegia; PMCA; calcium transient; neurodegeneration