title: Neuronal apoptosis inhibitory protein: Structural requirements for hippocalcin binding and effects on survival of NGF-dependent sympathetic neurons.
abstract: Neuronal apoptosis inhibitory protein (NAIP) has been linked to the inherited disease, spinal muscular atrophy (SMA), which occurs in children with degeneration of the motorneurons. In the nervous system, NAIP is expressed by specific classes of neurons including spinal motorneurons. Recently, NAIP was shown to interact with hippocalcin, which belongs to the neuronal calcium sensor (NCS) protein family. Here we have studied this interaction in more detail, using deletions and a mutagenesis of the third baculovirus inhibitory repeat (BIR) motif in NAIP, and functional assays for neuronal death. The results showed that specific amino acids and the zinc finger domain in BIR3 are needed for efficient interaction of NAIP with hippocalcin. Cotransfections of NAIP-BIR3 and hippocalcin resulted in translocation and colocalisation of the two proteins in neuroblastoma cells. This was accompanied by an enhanced resistance towards cell death induced by high levels of calcium. In contrast, expression of NAIP-BIR3 and hippocalcin in sympathetic neurons did not protect against death induced by nerve growth factor (NGF) withdrawal. The results demonstrate a functional interaction of hippocalcin with NAIP-BIR3, which in neuroblastoma cells leads to rescue of cells after high intracellular calcium, but which in sympathetic neurons had no significant effect. The results indicate that NAIP in conjunction with hippocalcin can affect the survival of some, but not all neural cells, and this interaction may play a role in the neurodegenerative processes in SMA, and possible other human disorders.
authors.affiliation: Department of Neuroscience, Neurobiology, Uppsala University, Biomedical Centre, Box 587, Uppsala, Sweden. dan.lindholm@neuro.uu.se
authors.forename: Dan
authors.initials: D
authors.lastname: Lindholm
authors.forename: Eric A
authors.initials: EA
authors.lastname: Mercer
authors.forename: Li Ying
authors.initials: LY
authors.lastname: Yu
authors.forename: Yuming
authors.initials: Y
authors.lastname: Chen
authors.forename: Jyrki
authors.initials: J
authors.lastname: Kukkonen
authors.forename: Laura
authors.initials: L
authors.lastname: Korhonen
authors.forename: Urmas
authors.initials: U
authors.lastname: Arumäe
mesh_terms: D000818:Animals; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002470:Cell Survival; D002478:Cells, Cultured; D005728:Ganglia, Sympathetic / Q000166:cytology*; D051597:Hippocalcin; D051034:Inhibitor of Apoptosis Proteins; D051379:Mice; D009154:Mutation; D020932:Nerve Growth Factor / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000737:chemistry* / Q000378:metabolism* / Q000502:physiology; D009447:Neuroblastoma; D051616:Neuronal Apoptosis-Inhibitory Protein; D009474:Neurons / Q000166:cytology / Q000187:drug effects; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry; D020449:Repetitive Sequences, Amino Acid; D017384:Sequence Deletion; D014407:Tumor Cells, Cultured; D020798:Two-Hybrid System Techniques
chemical_list: D002135:Calcium-Binding Proteins; C496692:Hpca protein, mouse; D051034:Inhibitor of Apoptosis Proteins; C496801:Naip1 protein, mouse; D009419:Nerve Tissue Proteins; D051616:Neuronal Apoptosis-Inhibitory Protein; D011506:Proteins; D051597:Hippocalcin; D020932:Nerve Growth Factor