LKB1 GENE TISSUE SPECIFIC KNOCKOUT MOUSE MODEL FOR PANCREATIC CANCER

Abstract

Pancreatic cancer is the fourth leading cause of cancer death in United States. Studies of the molecular genetics of pancreatic cancer as well as molecular biology of pancreatic development may advance our understanding of the mechanisms underlying the pathogenesis of this malignancy. Germline mutations in the LKB1 gene cause Peutz-Jeghers syndrome (PJS), which is characterized by gastrointestinal hamartomatous polyps and abnormal pigmentation. PJS is also a cancer predisposition syndrome with patients exhibiting an increased risk for developing a variety of different cancers including pancreatic cancer. It has been reported that patients with PJS have a 100-fold higher risk for development of pancreatic cancer than the general population and the lifetime-cumulated risk for this disease has been estimated to be 36%. LKB1 is also mutated in a significant proportion of sporadic pancreatic adenocarcinomas. To evaluate the role of LKB1 in pancreatic tumorigenesis, we have created a pancreatic tissue specific mouse model employing Cre-loxp technology. For this purpose, we cloned the mouse LKB1 gene and constructed an LKB1 targeting vector. The LKB13loxp allele with three loxp sites flanking the region of exons 2-8 and an adjacent neomycin resistance gene cassette were integrated into the genome as a result of homologous recombination in mouse ES cells. The chimeric mice derived from recombinant ES clones transmitted the LKB13loxp allele to the offspring. After the mating of LKB13loxp/+ with CMV-cre transgenic mouse, we obtained the LKB1+/− mouse line. Then a series of matings were carried out using LKB1+/− mice, LKB13loxp/+ mice and pdx-cre transgenic mice. The pdx promoter drives expression of Cre primarily in the pancreas, allowing us to generate pancreatic tissue specific null mice for the LKB1 gene (LKB13loxp/−/pdx-cre). Our preliminary data demonstrate that these mice develop intraductal papillary mucinous neoplasm (IPMN) as well as cystadenoma in their pancreata by the age of 4 months. These mice provide a model for studying the potential role of IPMN and cystadenomas in the development of pancreatic adenocarcinoma. IPMN have been implicated as a precursor lesion for human pancreatic adenocarcinoma. Because very little is known about these pancreatic lesions and the role of LKB1 in pancreatic carcinogenesis, the mouse model should be useful in future studies aimed at understanding how mutations in the LKB1 gene can lead to pancreatic cancer.