Pancreatic ductal adenocarcinomas (PDAC) are highly invasive and metastatic neoplasms commonly unresponsive to current drug therapy. Overwhelmingly, PDAC harbors early constitutive, oncogenic mutations in K-RasG12D that exist prior to invasion. Histologic and genetic analyses of human PDAC biopsies also exhibit increased expression of ERK1/2 and pro-invasive matrix metalloproteinases (MMPs); indicators of poor prognosis. However, the distinct molecular mechanisms necessary for K-Ras – ERK1/2 signaling and its influence on MMP-directed stromal invasion in primary human pancreatic ductal epithelial cells (PDECs) has yet to be elucidated in 3D. Expression of oncogenic K-RasG12D alone in genetically-defined PDECs reveals increased invadopodia and epithelial-to-mesenchymal transition markers, but only when cultured in a 3D model incorporating a basement membrane analog. Activation of extracellular signal-related kinase 2 (ERK2), but not ERK1, also occurs only in K-RasG12D mutated PDECs cultured in 3D and is a necessary intracellular signaling event for invasion based upon pharmacologic and shRNA inhibition. Increased active invasion of K-RasG12D PDECs through the basement membrane model is associated with a specific microarray gene expression signature and induction of MMP endopeptidases. Specifically, MMP-1 RNA, its secreted protein, and its proteolytic cleavage activity are amplified in K-RasG12D PDECs when assayed by RT q-PCR, ELISA, and fluorescence resonance energy transfer (FRET). Importantly, shRNA silencing of MMP-1 mimics ERK2 inhibition and disrupts active, vertical PDEC invasion. ERK2-isoform and MMP-1 targeting are shown to be viable strategies to attenuate invasion of K-RasG12D mutated human pancreatic cancer cells in a 3D tumor microenvironment.

Embryonic development of the pancreas is marked by an early phase of dramatic morphogenesis, in which pluripotent progenitor cells of the developing pancreatic epithelium give rise to the full array of mature exocrine and endocrine cell types. The genetic determinants of acinar and islet cell lineages are somewhat well defined; however, the molecular mechanisms directing ductal formation and differentiation remain to be elucidated. The complex ductal architecture of the pancreas is established by a reiterative program of progenitor cell expansion and migration known as branching morphogenesis, or tubulogenesis, which proceeds in mouse development concomitantly with peak Pdx1 transcription factor expression. We therefore evaluated Pdx1 expression with respect to lineage-specific markers in embryonic sections of the pancreas spanning this critical period of duct formation and discovered an unexpected population of nonislet Pdx1-positive cells displaying physical traits of branching. We then established a 3D cell culture model of branching morphogenesis using primary pancreatic duct cells and identified a transient surge of Pdx1 expression exclusive to branching cells. From these observations we propose that Pdx1 might be involved temporally in a program of gene expression sufficient to facilitate the biochemical and morphological changes necessary for branching morphogenesis. INTRODUCTIONThe primary function of the exocrine pancreas is to produce and secrete digestive enzymes for export to the small intestine. The collection and transport of these enzymes are facilitated by an intricate ductal network of branched epithelial tubules, such that enzymes secreted into smaller peripheral ducts ultimately feed into the larger main pancreatic duct, which in turn flows into the duodenum. This complex structure is established during embryonic development by a coordinated mechanism of progenitor cell proliferation and migration known as branching morphogenesis (Jorgensen et al., 2007). Some of the genetic and biochemical events directing this process are shared among the many organs served by ductal networks-such as the lung, breast, and kidney-and are also somewhat conserved across species (Lu and Werb, 2008). In general, branching morphogenesis is initiated by mesenchymal signaling to epithelial cell growth factor receptors, inducing multiple responses within those epithelial cells to 1) undertake temporary cytoskeletal reorganization that will facilitate cell motility, 2) inhibit proliferation, and 3) suppress the original mesenchymal growth factor signal (Metzger and Krasnow, 1999;Affolter et al., 2003). The specific mesenchymal growth factors and epithelial growth factor receptors, their cognate signaling pathways, and transcription factors involved in such processes contributing to branching morphogenesis in the pancreas are not well understood and remain to be elucidated.Pancreatic organogenesis is dependent on the homeodomain transcription factor Pdx1, as demonstrated by pancreatic agenesis observed in Pdx1-null mic...

Evasion from drug-induced apoptosis is a crucial mechanism of cancer treatment resistance. The proapoptotic protein NOXA marks an aggressive pancreatic ductal adenocarcinoma (PDAC) subtype. To identify drugs that unleash the death-inducing potential of NOXA, we performed an unbiased drug screening experiment. In NOXA-deficient isogenic cellular models, we identified an inhibitor of the transcription factor heterodimer CBFβ/RUNX1. By genetic gain and loss of function experiments, we validated that the mode of action depends on RUNX1 and NOXA. Of note is that RUNX1 expression is significantly higher in PDACs compared to normal pancreas. We show that pharmacological RUNX1 inhibition significantly blocks tumor growth in vivo and in primary patient-derived PDAC organoids. Through genome-wide analysis, we detected that RUNX1-loss reshapes the epigenetic landscape, which gains H3K27ac enrichment at the NOXA promoter. Our study demonstrates a previously unknown mechanism of NOXA-dependent cell death, which can be triggered pharmaceutically. Therefore, our data show a way to target a therapy-resistant PDAC, an unmet clinical need.