Inactivation of TIF1γ Cooperates with KrasG12D to Induce Cystic Tumors of the Pancreas

Inactivation of the Transforming Growth Factor Beta (TGF beta) tumor suppressor pathway contributes to the progression of Pancreatic Ductal AdenoCarcinoma (PDAC) since it is inactivated in virtually all cases of this malignancy. Genetic lesions inactivating this pathway contribute to pancreatic tumor progression in mouse models. Transcriptional Intermediary Factor 1 gamma (TIF1 gamma) has recently been proposed to be involved in TGF beta signaling, functioning as either a positive or negative regulator of the pathway. Here, we addressed the role of TIF1 gamma in pancreatic carcinogenesis. Using conditional Tif1 gamma knockout mice (Tif1 gamma(lox/lox)), we selectively abrogated Tif1 gamma expression in the pancreas of Pdx1-Cre;Tif1 gamma(lox/lox) mice. We also generated Pdx1-Cre;LSL-Kras(G12D);Tif1 gamma(lox/lox) mice to address the effect of Tif1 gamma loss-of-function in precancerous lesions induced by oncogenic Kras(G12D). Finally, we analyzed TIF1 gamma expression in human pancreatic tumors. In our mouse model, we showed that Tif1 gamma was dispensable for normal pancreatic development but cooperated with Kras activation to induce pancreatic tumors reminiscent of human Intraductal Papillary Mucinous Neoplasms (IPMNs). Interestingly, these cystic lesions resemble those observed in Pdx1-Cre;LSL-Kras(G12D);Smad4(lox/lox) mice described by others. However, distinctive characteristics, such as the systematic presence of endocrine pseudo-islets within the papillary projections, suggest that SMAD4 and TIF1 gamma don't have strictly redundant functions. Finally, we report that TIF1 gamma expression is markedly down-regulated in human pancreatic tumors by quantitative RT-PCR and immunohistochemistry supporting the relevance of these findings to human malignancy. This study suggests that TIF1 gamma is critical for tumor suppression in the pancreas, brings new insight into the genetics of pancreatic cancer, and constitutes a promising model to decipher the respective roles of SMAD4 and TIF1 gamma in the multifaceted functions of TGF beta in carcinogenesis and development.