Down-regulation of claudin-18 is associated with the proliferative and invasive potential of gastric cancer at the invasive front.
BACKGROUND
Claudins are known as tight junction proteins, and their expression pattern in gastric cancer is still controversial. The relationship between the expression patterns of tight junction proteins and tumor proliferation in early gastric cancer is still far from clear.


OBJECTIVE
To investigate the expression patterns of claudin-18 and Ki-67 in early gastric cancer at the invasive front and surrounding normal gastric mucosa and to investigate the biological function of claudin-18 in the proliferation and invasion of cancer cells.


METHODS
Seventy-five early gastric cancer lesions removed via endoscopic mucosal resection or endoscopic submucosal resection were evaluated. All gastric cancer lesions were diagnosed as differentiated adenocarcinoma using the Japanese Classification of Gastric Carcinoma. To assess epithelial proliferation, immunostaining with Ki-67 was performed, and the labeling index was calculated. To assess the expression of epithelial tight junction proteins, immunofluorescent staining of claudin-18 was performed. The immunoreactivity of claudin-18 was graded according to the number of stained cells. Correlation analysis was performed by Spearman's rank correlation coefficient. Transfection of claudin-18 small interfering RNA (siRNA) was accomplished in MKN74, a claudin-18-positive gastric cancer cell line, to investigate the effect of claudin-18 on proliferation and invasion of cancer cells.


RESULTS
Claudin-18 was significantly down-regulated in gastric cancer compared to surrounding gastric normal mucosa or intestinal metaplasia. The Ki-67 labeling index of gastric cancer at the invasive front was inversely correlated with the claudin-18 level, but that at the mucosal lesion was not correlated. Claudin-18 knockdown significantly promoted the proliferation of MKN74 compared with control siRNA-transfected cells. MKN74 invasion increased significantly with claudin-18 siRNA transfection compared with control siRNA transfection.


CONCLUSIONS
Down-regulation of claudin-18 is associated with the proliferative potential at the invasive front of gastric cancer, suggesting that it has a pivotal role in gastric cancer progression.
Division of Upper Gastroenterology, Department of Internal Medicine, Hyogo College of Medicine, Nishinomiya, Hyogo, Japan.
Tadayuki
T
Oshima
Jing
J
Shan
Takuya
T
Okugawa
Xin
X
Chen
Kazutoshi
K
Hori
Toshihiko
T
Tomita
Hirokazu
H
Fukui
Jiro
J
Watari
Hiroto
H
Miwa
D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology*; D000368:Aged; D017209:Apoptosis; D015153:Blotting, Western; D002465:Cell Movement; D049109:Cell Proliferation; D057167:Claudins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018450:Disease Progression; D015536:Down-Regulation; D005260:Female; D005455:Fluorescent Antibody Technique; D005753:Gastric Mucosa / Q000378:metabolism / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007124:Immunoenzyme Techniques; D008297:Male; D009361:Neoplasm Invasiveness; D009367:Neoplasm Staging; D011379:Prognosis; D034741:RNA, Small Interfering / Q000235:genetics; D013274:Stomach Neoplasms / Q000378:metabolism / Q000473:pathology*; D014407:Tumor Cells, Cultured
C486683:CLDN18 protein, human; D057167:Claudins; D034741:RNA, Small Interfering