DNMT1 Expression and DNA Methylation in Intraductal Papillary Neoplasms of the Bile Duct

Intraductal papillary neoplasms of the bile duct (IPNB) are histologically and clinically classified as type 1 and 2. This study aimed to identify the differences between these two types.

Based on multiple gene expression analysis (MGEA) using type 1, type 2, and pancreatic intraductal papillary mucinous neoplasms (n=4, 6, and 5, respectively), immunohistochemistry of DNMT1 and methylation-specific PCR for p16, APC, BRCA1, hMLH1, TIMP3, and SOX17 were performed on type 1 and 2 IPNBs (n=14, each).

The DNMT1 protein was highly expressed (p<0.001) in 28.6% of type 1 cases and all type 2 cases. The DNA methylation ratio for the six genes in total as well as for SOX17 was lower in type 1 than in type 2 (p<0.05 each).

Type 2 IPNB showed increased DNMT1 protein expression and increased DNA methylation frequency of the examined tumor suppressor genes compared to type 1. DNMT1 IHC may be helpful in discriminating between these two types.