Purpose: Intraductal papillary mucinous neoplasm (IPMN) of the pancreas is an increasingly identified precursor to infiltrating ductal adenocarcinoma. Although our knowledge of the clinical and pathologic features of IPMNs is increasing, the molecular mechanisms underlying these neoplasms remain poorly understood.
Experimental designs: To provide further insight into the molecular pathobiology of IPMNs, global expression profiling was done to determine genes that are inactivated/down-regulated in IPMNs using oligonucleotide microarrays (Affymetrix).
Results: In total, 300 unique transcripts (217 known genes) were identified as highly underexpressed in 12 IPMNs (<10-fold lower and P < 0.05) compared with five normal pancreatic ductal epithelium samples obtained by laser capture microdissection. The differential expression of a selection of genes was confirmed using reverse-transcription PCR. One of the genes underexpressed at both the transcriptional and protein level in a significant proportion of IPMNs was the cyclin-dependent kinase inhibitor, CDKN1C/p57KIP2. CDKN1C expression was also decreased in many pancreatic cancer cell lines and was restored following treatment with a DNA methylation inhibitor (5-aza-2'-deoxycitidine) or, more potently, with a histone deacetylase inhibitor (trichostatin A). Partial methylation of the CDKN1C promoter CpG island was found in most, but not all, pancreatic cancer cell lines with reduced CDKN1C expression, and was also detectable in IPMNs. Furthermore, a subset of pancreatic cancers showed complete hypomethylation of LIT1, an imprinting control region important for the regulation of CDKN1C expression. Complete hypomethylation in these cancers was the result of deletion of the methylated LIT1 allele at 11p15.5 rather than loss of imprinting.
Conclusions: These findings suggest that CDKN1C is commonly down-regulated in pancreatic ductal neoplasms through a combination of promoter hypermethylation, histone deacetylation, and loss of the maternal allele expressing CDKN1C.