Overexpression of Midkine in Pancreatic Duct Adenocarcinomas Induced by N‐Nitrosobis(2‐oxopropyl)amine in Hamsters and Their Cell Lines

The expression of midkine (MK) was investigated in pancreatic ductal hyperplasias, atypical hyperplasias and adenocarcinomas induced by N‐nitrosobis(2‐oxopropyl)amine (BOP) in hamsters, and in hamster ductal adenocarcinoma cell lines (HPD‐1NR, ‐2NR and ‐3NR). MK mRNA was clearly overexpressed in invasive pancreatic duct adenocarcinomas (PCs) and the three cell lines as assessed by northern blot analysis, and MK protein expression increased from ductal hyperplasia through atypical hyperplasias, intraductal carcinomas and invasive PCs by immunohistochemistry. The extent of overexpression of MK mRNA in PCs was almost the same as in hamster whole embryonic tissue. MK is reported to be a retinoid‐responsive gene, but MK mRNA expression was not affected by treatment with all‐trans retinoic acid (tRA) or N‐(4‐hydroxyphenyl)retinamide (4‐ HPR) in HPD‐1NR cells. The results thus suggest that MK expression is involved in the development and progression of pancreatic ductal adenocarcinomas induced by BOP in hamsters, with loss of upregulation by retinoic acid.