Pancreatic ductal adenocarcinoma (PDAC), a poor prognostic cancer, commonly develops following activating mutations in the KRAS oncogene. Activation of WNT signaling is also commonly observed in PDAC. To ascertain the impact of postnatal activation of WNT-stimulated signaling pathways in PDAC development, we combined the Elastase-tva-based RCAS-TVA pancreatic cancer model with the established LSL-KrasG12D, Ptf1a-cre model. Delivery of RCAS viruses encoding beta-cateninS37A and WNT1 stimulated the progression of premalignant pancreatic intraepithelial neoplasias (PanIN) and PDAC development. Moreover, mice injected with RCAS-beta-cateninS37A or RCAS-Wnt1 had reduced survival relative to RCAS-GFP-injected controls (P < .05). Ectopic expression of active beta-catenin, or its DNA-binding partner TCF4, enhanced transformation associated phenotypes in PDAC cells. In contrast, these phenotypes were significantly impaired by the introduction of ICAT, an inhibitor of the beta-catenin/TCF4 interaction. By gene expression profiling, we identified Cyr61 as a target molecule of the WNT/beta-catenin signaling pathway in pancreatic cancer cells. Nuclear beta-catenin and CYR61 expression were predominantly detected in moderately to poorly differentiated murine and human PDAC. Indeed, nuclear beta-catenin- and CYR61-positive PDAC patients demonstrated poor prognosis (P < .01). Knockdown of CYR61 in a beta-catenin-activated pancreatic cancer cell line reduced soft agar, migration and invasion activity. Together, these data suggest that the WNT/beta-catenin signaling pathway enhances pancreatic cancer development and malignancy in part via up-regulation of CYR61.

Mutation of KRAS is a common initiating event in pancreatic ductal adenocarcinoma (PDAC). Yet, the specific roles of KRAS-stimulated signaling pathways in the transformation of pancreatic ductal epithelial cells (PDEC), putative cells of origin for PDAC, remain unclear. Here, we show that KRAS(G12D) and BRAF(V600E) enhance PDEC proliferation and increase survival after exposure to apoptotic stimuli in a manner dependent on MEK/ERK and PI3K/AKT signaling. Interestingly, we find that activation of PI3K/AKT signaling occurs downstream of MAP-ERK kinase (MEK), and is dependent on the autocrine activation of the insulin-like growth factor (IGF) receptor (IGF1R) by IGF2. Importantly, IGF1R inhibition impairs KRAS(G12D)- and BRAF(V600E)-induced survival, whereas ectopic IGF2 expression rescues KRAS(G12D)- and BRAF(V600E)-mediated survival downstream of MEK inhibition. Moreover, we show that KRAS(G12D)- and BRAF(V600E)-induced tumor formation in an orthotopic model requires IGF1R. Interestingly, we show that while individual inhibition of MEK or IGF1R does not sensitize PDAC cells to apoptosis, their concomitant inhibition reduces survival. Our findings identify a novel mechanism of PI3K/AKT activation downstream of activated KRAS, illustrate the importance of MEK/ERK, PI3K/AKT, and IGF1R signaling in pancreatic tumor initiation, and suggest potential therapeutic strategies for this malignancy.

Pancreatic cancer is the 4th leading cause of cancer related death in the United States with a median survival time of less than 6 months. Pancreatic ductal adenocarcinoma (PDAC) accounts for greater than 85% of all pancreatic cancers, and is marked by early and frequent mutation of the KRAS oncogene, with activating KRAS mutations present in over 90% of PDAC. To date, though, targeting activated KRAS for cancer treatment has been very difficult, and targeted therapies are currently being sought for the downstream effectors of activated KRAS. Activation of KRAS stimulates multiple signaling pathways, including the MEK-ERK and PI3K-AKT signaling cascades, but the role of downstream effectors in pancreatic tumor initiation and progression remains unclear. I therefore used primary pancreatic ductal epithelial cells (PDECs), the putative cell of origin for PDAC, to determine the role of specific downstream signaling pathways in KRAS activated pancreatic tumor initiation. As one third of KRAS wild type PDACs harbor activating mutations in BRAF , and KRAS and BRAF mutations appear to be mutually exclusive, I also sought to determine the effect of activated BRAF (BRAF V600E ) expression on PDECs and the signaling requirements downstream of BRAF. I found that both KRAS G12D and BRAF V600E expressing PDECs displayed increased proliferation relative to GFP expressing controls, as well as increased PDEC survival after challenge with apoptotic stimuli. This survival was found to depend on both the MEK-ERK and PI3K-AKT signaling cascades. Surprisingly, I found that this survival is also dependent on the IGF1R, and that activation of PI3K/AKT signaling occurs downstream of MEK/ERK activation, and is dependent on signaling through the IGF1R. Consistent with this, I find increased IGF2 expression in KRAS G12D and BRAF V600E expressing PDECs, and show that ectopic expression of IGF2 rescues survival in PDECs with inhibited MEK, but not PI3K. Finally, I showed that the expression of KRAS G12D or BRAF V600E in PDECs lacking both the Ink4a/Arf and Trp53 tumor suppressors is sufficient for tumor formation following orthotopic transplant of PDECs, and that IGF1R knockdown impairs KRAS and BRAF-induced tumor formation in this model. In addition to these findings within PDECs, I demonstrate that KRAS G12D or BRAF V600E expressing tumor cell lines differ in MEK-ERK and PI3K-AKT signaling from PDECs. In contrast to KRAS G12D or BRAF V600E expressing PDECs, activation of AKT at serine 473 in the KRAS G12D or BRAF V600E expressing tumor cell lines does not lie downstream of MEK, and only the inhibition of PI3K alone or both MEK and the IGF1R simultaneously results in loss of tumor cell line survival. However, inhibition of MEK, PI3K, or the IGF1R in KRAS G12D or BRAF V600E expressing tumor cell lines also resulted in decreased proliferation relative to DMSO treated cells, demonstrating that all three signaling cascades remain important for tumor cell growth and are therefore viable options for pancreatic cancer therapeutics.

Pancreatic ductal adenocarcinoma (PDAC), one of the most aggressive human malignancies, is thought to be initiated by KRAS activation. Here we find that transcriptional activation mediated by the Gli family of transcription factors, although dispensable for pancreatic development, is required for Kras-induced proliferation and survival in primary pancreatic epithelial cells in culture and for Kras-driven pancreatic intraepithelial neoplasia and PDAC formation in vivo. Further, ectopic Gli1 activation in the mouse pancreas accelerates Kras-driven tumor formation, underscoring the importance of Gli transcription factors in pancreatic tumorigenesis. Interestingly, we demonstrate Gli-regulated I-kappa-B kinase epsilon (IKBKE) and NF-kappaB activity in pancreatic cancer cells and show that this activity is a critical downstream mediator for Gli-dependent PDAC cell transformation and survival. Together, these studies demonstrate the requirement for Gli in Kras-dependent pancreatic epithelial transformation, suggest a mechanism of Gli-NF-kappaB oncogenic activation, and provide genetic evidence supporting the therapeutic targeting of Gli activity in pancreatic cancer.