Oncogenic KRAS Requires Complete Loss of BAP1 Function for Development of Murine Intrahepatic Cholangiocarcinoma

Abstract

Intrahepatic cholangiocarcinoma (ICC) is a primary biliary malignancy that harbors a dismal prognosis. Oncogenic mutations of KRAS and loss of function mutations of BRCA1-associated protein 1 (BAP1) have been identified as recurrent somatic alterations in ICC. However, an autochthonous genetically engineered mouse model of ICC that genocopies the co-occurrence of these mutations has never been developed. By crossing Albumin-Cre mice bearing conditional alleles of mutant Kras and/or floxed Bap1, Cre-mediated recombination within the liver was induced. Mice with hepatic expression of mutant Kras^G12D alone (KA), bi-allelic loss of hepatic Bap1 (B^homoA), and heterozygous loss of Bap1 in conjunction with mutant Kras^G12D expression (B^hetKA) developed primary hepatocellular carcinoma (HCC), but no discernible ICC. In contrast, mice with homozygous loss of Bap1 in conjunction with mutant Kras^G12D expression (B^homoKA) developed discrete foci of HCC and ICC. Further, the median survival of B^homoKA mice was significantly shorter at 24 weeks, when compared to median survival of ≥40 weeks in B^hetKA mice and approximately 50 weeks in B^homoA and KA mice (p <0.001). Microarray analysis performed on liver tissue from KA and B^homoKA mice identified differentially expressed genes in the setting of BAP1 loss and suggests that deregulation of ferroptosis might be one mechanism by which loss of BAP1 cooperates with oncogenic Ras in hepato-biliary carcinogenesis. Our autochthonous model provides an in vivo platform to further study this lethal class of neoplasm.