Syntaxin 4 regulates the surface localization of a promyogenic receptor Cdo thereby promoting myogenic differentiation.
BACKGROUND
Syntaxins are a family of membrane proteins involved in vesicle trafficking, such as synaptic vesicle exocytosis. Syntaxin 4 (Stx4) is expressed highly in skeletal muscle and plays a critical role in insulin-stimulated glucose uptake by promoting translocation of glucose transporter 4 (GLUT4) to the cell surface. A cell surface receptor cell adhesion molecule-related, down-regulated by oncogenes (Cdo) is a component of cell adhesion complexes and promotes myoblast differentiation via activation of key signalings, including p38MAPK and AKT. In this study, we investigate the function of Stx4 in myoblast differentiation and the crosstalk between Stx4 and Cdo in myoblast differentiation.


METHODS
The effects of overexpression or shRNA-based depletion of Stx4 and Cdo genes on C2C12 myoblast differentiation are assessed by Western blotting and immunofluorescence approaches. The interaction between Cdo and Stx4 and the responsible domain mapping are assessed by coimmunoprecipitation or pulldown assays. The effect of Stx4 depletion on cell surface localization of Cdo and GLUT4 in C2C12 myoblasts is assessed by surface biotinylation and Western blotting.


RESULTS
Overexpression or knockdown of Stx4 enhances or inhibits myogenic differentiation, respectively. Stx4 binds to the cytoplasmic tail of Cdo, and this interaction seems to be critical for induction of p38MAPK activation and myotube formation. Stx4 depletion decreases specifically the cell surface localization of Cdo without changes in surface N-Cadherin levels. Interestingly, Cdo depletion reduces the level of GLUT4 and Stx4 at cell surface. Consistently, overexpression of Cdo in C2C12 myoblasts generally increases glucose uptake, while Cdo depletion reduces it.


CONCLUSIONS
Stx4 promotes myoblast differentiation through interaction with Cdo and stimulation of its surface translocation. Both Cdo and Stx4 are required for GLUT4 translocation to cell surface and glucose uptake in myoblast differentiation.
Research Center for Cell Fate Control, College of Pharmacy, Sookmyung Women's University, Seoul, 140-742 Republic of Korea.
Miran
M
Yoo
Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Samsung Biomedical Research Institute, Suwon, 440-746 Republic of Korea.
Bok-Geon
BG
Kim
Research Center for Cell Fate Control, College of Pharmacy, Sookmyung Women's University, Seoul, 140-742 Republic of Korea.
Sang-Jin
SJ
Lee
Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Samsung Biomedical Research Institute, Suwon, 440-746 Republic of Korea.
Hyeon-Ju
HJ
Jeong
Research Center for Epigenome Regulation, School of Pharmacy, Sungkyunkwan University, Suwon, Republic of Korea.
Jong Woo
JW
Park
College of Pharmacy, Dankook University, Cheonan, 330-714 Republic of Korea.
Dong-Wan
DW
Seo
Research Center for Cell Fate Control, College of Pharmacy, Sookmyung Women's University, Seoul, 140-742 Republic of Korea.
Yong Kee
YK
Kim
Department of Pharmacology, Myunggok Medical Research Institute, College of Medicine, Konyang University, Daejeon, Republic of Korea.
Hoi Young
HY
Lee
Research Center for Epigenome Regulation, School of Pharmacy, Sungkyunkwan University, Suwon, Republic of Korea.
Jeung-Whan
JW
Han
Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Samsung Biomedical Research Institute, Suwon, 440-746 Republic of Korea.
Jong-Sun
JS
Kang
Research Center for Cell Fate Control, College of Pharmacy, Sookmyung Women's University, Seoul, 140-742 Republic of Korea.
Gyu-Un
GU
Bae
Cdo; Cell surface localization; Myogenic differentiation; Syntaxin 4; p38MAPK