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Overexpression of G₁-S Cyclins and Cyclin-Dependent Kinases during Multistage Human Pancreatic Duct Cell Carcinogenesis

¹ Department of Pathology and ² Division of Cellular and Molecular Biology, University Health Network–Princess Margaret Hospital and Ontario Cancer Institute; and ³ Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, Toronto, Ontario, Canada

Purpose: Molecular analysis of pancreatic intraepithelial neoplasia lesions and ductal adenocarcinoma suggested a multistage paradigm for pancreatic duct cell carcinogenesis. This study investigated the molecular basis for the neoplastic duct cells in this pancreatic intraepithelial neoplasia–carcinoma sequence to acquire progressive enhancement of their proliferative potential.

Experimental Design: Using tissue microarray blocks containing 15 to 40 pancreatic intraepithelial neoplasia lesions and ductal adenocarcinoma of pancreas, we studied by immunohistochemistry the expression profiles of cyclins and cyclin dependent kinases (CDKs) that regulate the G₁-S cell cycle checkpoints. The role of cyclins D3 and D1 in three pancreatic cancer cell lines was investigated using specific short interfering RNA technique.

Results: Cyclin D3 overexpression was noted the earliest in pancreatic intraepithelial neoplasia-1A and was prevalent in 90% to 100% of high-grade pancreatic intraepithelial neoplasias and ductal cancer. Cyclin A overexpression was also noted early and reached 50% to 100% of high-grade pancreatic intraepithelial neoplasias and cancer, but the percentage of abnormal duct cells showing overexpression of cyclin A was significantly lower than cyclin D3. Cyclin E overexpression occurred in 20% to 25% of high-grade pancreatic intraepithelial neoplasias and in 75% of ductal carcinoma. Cyclin D1 demonstrated the lowest frequency of overexpression that occurred late. CDK2 and CDK4 overexpression was also noted in early pancreatic intraepithelial neoplasias and progressively increased to reach 60% to 75% in carcinoma. The down-regulation of cyclin D3 mRNA and protein levels using specific short interfering RNA resulted in growth inhibition of pancreatic cancer cell lines.

Conclusion: The results provide additional insight into the mechanism of G₁-S cell cycle checkpoints deregulation during stepwise pancreatic duct cell carcinogenesis, and suggest a p16-independent role for cyclin D3 in deregulating the G₁ cell cycle checkpoints during early stages of pancreatic duct cell carcinogenesis.

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