N-ethylmaleimide-sensitive factor interacts with the serotonin transporter and modulates its trafficking: implications for pathophysiology in autism.
BACKGROUND
Changes in serotonin transporter (SERT) function have been implicated in autism. SERT function is influenced by the number of transporter molecules present at the cell surface, which is regulated by various cellular mechanisms including interactions with other proteins. Thus, we searched for novel SERT-binding proteins and investigated whether the expression of one such protein was affected in subjects with autism.


METHODS
Novel SERT-binding proteins were examined by a pull-down system. Alterations of SERT function and membrane expression upon knockdown of the novel SERT-binding protein were studied in HEK293-hSERT cells. Endogenous interaction of SERT with the protein was evaluated in mouse brains. Alterations in the mRNA expression of SERT (SLC6A4) and the SERT-binding protein in the post-mortem brains and the lymphocytes of autism patients were compared to nonclinical controls.


RESULTS
N-ethylmaleimide-sensitive factor (NSF) was identified as a novel SERT-binding protein. NSF was co-localized with SERT at the plasma membrane, and NSF knockdown resulted in decreased SERT expression at the cell membranes and decreased SERT uptake function. NSF was endogenously co-localized with SERT and interacted with SERT. While SLC6A4 expression was not significantly changed, NSF expression tended to be reduced in post-mortem brains, and was significantly reduced in lymphocytes of autistic subjects, which correlated with the severity of the clinical symptoms.


CONCLUSIONS
These data clearly show that NSF interacts with SERT under physiological conditions and is required for SERT membrane trafficking and uptake function. A possible role for NSF in the pathophysiology of autism through modulation of SERT trafficking, is suggested.
Research Center for Child Mental Development, University of Fukui, Fukui, Japan ; Department of Development of Functional Brain Activities, United Graduate School of Child Development, Osaka University, Kanazawa University, Hamamatsu University School of Medicine, Chiba University and University of Fukui, Fukui, Japan.
Keiko
K
Iwata
Research Center for Child Mental Development, University of Fukui, Fukui, Japan ; Department of Development of Functional Brain Activities, United Graduate School of Child Development, Osaka University, Kanazawa University, Hamamatsu University School of Medicine, Chiba University and University of Fukui, Fukui, Japan ; Research Center for Child Mental Development, Hamamatsu University School of Medicine, Hamamatsu, Japan.
Hideo
H
Matsuzaki
Department of Bioengineering, Graduate School of Engineering, Osaka City University, Osaka, Japan.
Taro
T
Tachibana
Department of Anatomy, Hamamatsu University School of Medicine, Hamamatsu, Japan.
Koji
K
Ohno
Department of Bioengineering, Graduate School of Engineering, Osaka City University, Osaka, Japan.
Saori
S
Yoshimura
Department of Molecular Brain Science, United Graduate School of Child Development, Osaka University, Kanazawa University, Hamamatsu University School of Medicine, Chiba University and University of Fukui, Suita, Osaka, Japan ; Molecular Research Center for Children's Mental Development, United Graduate School of Child Development, Osaka University, Suita, Osaka, Japan.
Hironori
H
Takamura
Department of Molecular Brain Science, United Graduate School of Child Development, Osaka University, Kanazawa University, Hamamatsu University School of Medicine, Chiba University and University of Fukui, Suita, Osaka, Japan ; Molecular Research Center for Children's Mental Development, United Graduate School of Child Development, Osaka University, Suita, Osaka, Japan.
Kohei
K
Yamada
Department of Molecular Brain Science, United Graduate School of Child Development, Osaka University, Kanazawa University, Hamamatsu University School of Medicine, Chiba University and University of Fukui, Suita, Osaka, Japan.
Shinsuke
S
Matsuzaki
Department of Psychiatry, Hamamatsu University School of Medicine, Hamamatsu, Japan.
Kazuhiko
K
Nakamura
Research Center for Child Mental Development, Hamamatsu University School of Medicine, Hamamatsu, Japan.
Kenji J
KJ
Tsuchiya
Research Center for Child Mental Development, Hamamatsu University School of Medicine, Hamamatsu, Japan.
Kaori
K
Matsumoto
Research Center for Child Mental Development, Hamamatsu University School of Medicine, Hamamatsu, Japan ; Faculty of Contemporary Sociology, Chukyo University, Toyota, Japan.
Masatsugu
M
Tsujii
Department of Child and Adolescent Psychiatry, Hamamatsu University School of Medicine, Hamamatsu, Japan.
Toshirou
T
Sugiyama
Department of Molecular Brain Science, United Graduate School of Child Development, Osaka University, Kanazawa University, Hamamatsu University School of Medicine, Chiba University and University of Fukui, Suita, Osaka, Japan.
Taiichi
T
Katayama
Research Center for Child Mental Development, Hamamatsu University School of Medicine, Hamamatsu, Japan ; Department of Psychiatry, Hamamatsu University School of Medicine, Hamamatsu, Japan.
Norio
N
Mori
Autism; Interaction; Lymphocyte; Membrane trafficking; NSF; Post-mortem brain; Serotonin transporter