The Journal of Neuroscience, July 1, 2002, 22(13):5354-5364
Synaptic and Nuclear Localization of Brain-Enriched Guanylate
Kinase-Associated Protein
Ikuko
Yao,
Junko
Iida,
Wataru
Nishimura, and
Yutaka
Hata
Department of Medical Biochemistry, Graduate School of Medicine,
Tokyo Medical and Dental University, Bunkyo-ku, Tokyo 113-8519, Japan
Brain-enriched guanylate kinase-associated protein (BEGAIN)
interacts with postsynaptic density (PSD)-95/synapse-associated protein
(SAP) 90. In immunohistochemistry and immunocytochemistry, BEGAIN was
detected in nuclei and at synapses in neurons. Nuclear localization was
also confirmed through subcellular fractionation. BEGAIN was localized
exclusively in nuclei when expressed in epithelial cells. These
findings led us to analyze the mechanism to determine the subcellular
localization of BEGAIN in neurons. Green fluorescent protein
(GFP)-tagged BEGAIN appeared first in nuclei and subsequently accumulated at dendrites. Approximately 75 and 90% of GFP-BEGAIN clusters were colocalized with synaptophysin and PSD-95/SAP90, respectively. GFP-protein containing only the N-terminal region also
formed foci in nuclei and clusters at dendrites. The N-terminal BEGAIN
was not precisely targeted to synapses, although it was partially
localized at synapses, possibly through dimer formation with endogenous
BEGAIN. The truncated form of PSD-95/SAP90 containing the guanylate
kinase domain blocked synaptic targeting of BEGAIN but did not affect
cluster formation at dendrites. NMDA receptor antagonists blocked
localization of GFP-BEGAIN at synapses but did not affect recruitment
to dendrites. These results suggest that BEGAIN is recruited to
dendrites by the N-terminal region independently of NMDA receptor
activity and that synaptic targeting of BEGAIN depends on NMDA receptor
activity and may be mediated by interaction with PSD-95/SAP90.
Key words:
BEGAIN; PSD-95/SAP90; NMDA receptor; synapse; nucleus; dendrite
Copyright © 2002 Society for Neuroscience 0270-6474/02/22135354-11$05.00/0