Abstract B15: Defining functional PDAC-suppressive mechanisms of the acinar differentiation factor PTF1A
Authors: Krah Nathan M. , Narayanan Shuba M. , Yugawa Deanne E. , Murtaugh L Charles 
Published: December 2016

The primary goal of this study is to define the cell-intrinsic and cell-extrinsic mechanisms that lead to PDAC initiation in the absence of the acinar differentiation determinant PTF1A. PDAC development is a dynamic process that involves both alterations within the pancreatic epithelium and crosstalk with immune cells. Our lab and others have demonstrated that PanINs and PDAC arise through KRASG12D-mediated dedifferentiation and transformation of mature acinar cells, despite the cancer’s duct-like phenotype. Acinar-to-PanIN transformation, while typically inefficient, is greatly accelerated by caerulein-induced pancreatitis, highlighting the synergy between cell-intrinsic alterations, such as KRAS mutation, and cell-extrinsic influences, including inflammation. Recently, we identified another cell-intrinsic change that greatly hastens PanIN development: loss of acinar cell identity, via downregulation or deletion of the master acinar transcription factor, PTF1A. Since loss of differentiation has consequences both within the acinar cell and on the surrounding microenvironment, we want to understand what cell-autonomous and non-cell autonomous changes drive PDAC initiation following Ptf1a deletion. In this study we address two major questions: first, does SOX9 mediate acinar-to-ductal reprogramming (ADR) within acinar cells following Ptf1a deletion? And second, does Ptf1a deletion alter immune cell infiltration to influence tumorigenesis?

Deletion of Ptf1a alone causes ADR and robust upregulation of the lineage-restricted ductal transcription factor SOX9. As previous studies have shown a requirement for the Sox9 gene in PanIN formation, we hypothesized that SOX9 is required to reprogram acinar cells to a tumor-susceptible state upon loss of PTF1A. In order to test this hypothesis, we have generated inducible, acinar specific, Ptf1a/Sox9 double knock-out mice. We are currently using these mice to determine the regulatory relationship between these key transcription factors in ADR and PanIN development, and we will present our preliminary findings at this meeting.

Our recently published work additionally suggests that deletion of Ptf1a leads to numerous changes outside of the acinar cells themselves, including upregulation of fibro-inflammatory pathways associated with PDAC. These data suggest that acinar-intrinsic changes influence the stromal microenvironment, and lead us to hypothesize that acinar cell differentiation is a critical determinant of how Kras-mutant cells activate and respond to the immune system during tumor initiation. To begin to test this hypothesis, we characterized the immune cell infiltrate in pancreata from KrasG12D mice in which tumor initiation was stimulated either by caerulein-induced pancreatitis (KRAS/caerulein mice) or Ptf1a deletion (KRAS/cKO mice). While pancreata of both groups had abundant macrophage infiltration, we found that T-cell infiltration was more pronounced in KRAS/cKO mice than KRAS/caerulein mice. These data suggest that dedifferentiation has a non-cell-autonomous effect on the response of the immune system to Kras-mutant precancerous cells. We next wanted to test whether dedifferentiation changed the response of the precancerous microenvironment to anti-inflammatory agents such as dexamethasone (DEX), which has been previously shown to inhibit PanIN formation. Consistent with previous results, we found that DEX alleviated PanIN formation and preserved histologically normal acinar tissue in KRAS/caerulein mice, which retain wild-type PTF1A. Paradoxically, however, DEX treatment enhanced PanIN formation in KRAS/cKO mice, indicating that PTF1A-mediated differentiation pathways are required for the anti-tumor effects of this commonly-used drug. In ongoing studies, we will use these genetic and pharmacological tools to determine what inflammatory cells and signals are required for ADR and subsequent PanIN initiation.

Citation Format: Nathan M. Krah, Shuba M. Narayanan, Deanne E. Yugawa, L Charles Murtaugh.{Authors}. Defining functional PDAC-suppressive mechanisms of the acinar differentiation factor PTF1A. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B15.