Brain-specific BNIP-2-homology protein Caytaxin relocalises glutaminase to neurite terminals and reduces glutamate levels.
Human Cayman ataxia and mouse or rat dystonia are linked to mutations in the genes ATCAY (Atcay) that encode BNIP-H or Caytaxin, a brain-specific member of the BNIP-2 family. To explore its possible role(s) in neuronal function, we used protein precipitation and matrix-assisted laser desorption/ionisation mass spectrometry and identified kidney-type glutaminase (KGA) as a novel partner of BNIP-H. KGA converts glutamine to glutamate, which could serve as an important source of neurotransmitter. Co-immunoprecipitation with specific BNIP-H antibody confirmed that endogenous BNIP-H and KGA form a physiological complex in the brain, whereas binding studies showed that they interact with each other directly. Immunohistochemistry and in situ hybridisation revealed high BNIP-H expression in hippocampus and cerebellum, broadly overlapping with the expression pattern previously reported for KGA. Significantly, BNIP-H expression was activated in differentiating neurons of the embryonic carcinoma cell line P19 whereas its overexpression in rat pheochromocytoma PC12 cells relocalised KGA from the mitochondria to neurite terminals. It also reduced the steady-state levels of glutamate by inhibiting KGA enzyme activity. These results strongly suggest that through binding to KGA, BNIP-H could regulate glutamate synthesis at synapses during neurotransmission. Thus, loss of BNIP-H function could render glutamate excitotoxicity or/and deregulated glutamatergic activation, leading to ataxia, dystonia or other neurological disorders.
Buschdorf
Jan Paul
JP
Department of Biological Sciences, 14 Science Drive 4, Faculty of Science, National University of Singapore, Singapore 117543, Republic of Singapore.
Li Chew
Li
L
Zhang
Bin
B
Cao
Qiong
Q
Liang
Feng-Yi
FY
Liou
Yih-Cherng
YC
Zhou
Yi Ting
YT
Low
Boon Chuan
BC
D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000166:cytology; D018236:Carcinoma, Embryonal / Q000378:metabolism / Q000473:pathology; D002454:Cell Differentiation; D002478:Cells, Cultured; D005260:Female; D005971:Glutamates / Q000378:metabolism*; D005972:Glutaminase / Q000378:metabolism*; D006801:Humans; D007668:Kidney / Q000378:metabolism; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D016501:Neurites / Q000201:enzymology*; D011817:Rabbits; D051381:Rats
D005971:Glutamates; D009419:Nerve Tissue Proteins; C508764:atcay protein, rat; D005972:Glutaminase