PROJECT SUMMARY Acinar epithelial cells can undergo a highly regulated acinar-to-ductal metaplasia (ADM), wherein resident acinar cells of the pancreas undergo trans-differentiation into ductal-like cells. In the context of damage to pancreas (pancreatitis), this process is adaptive and apparently reversible, where the ductal-like cells that have undergone ADM completely restore their acinar identity by undergoing acinar cell reprogramming. However, in the presence of mutant Kras, ADM cells remain ductal and are unable to reprogram into acinar cells, forcing their continued development down the ductal lineage. We have identified central molecular determinants of ADM, including key transcription factors such Prrx1 and Sox9. Despite this, very little remains known regarding the alterations that distinguish “adaptive” ADM (i.e. pancreatitis or injury-induced), which does not result in PanIN (preneoplasia), from “oncogenic” ADM (i.e. mutant Kras induced), which does. Additional features of ADM process are unknown – namely, what ‘gatekeepers’ control trans- differentiation of acinar cells and how the pancreas microenvironment participates in these cell fate transitions. Our objective is to study acinar cell fate and to define the key points at which the tightly regulated process of ADM is dysregulated. First, in several prior studies, we have defined Prrx1 as a central determinant of ADM formation. Second, we have begun to identify differences in the chromatin landscape of adaptive versus oncogenic ADM and highlight the AP-1 member Fra1 as a firm mediator distinguishing oncogenic and adaptive ADM through new in vivo data. Third, we have identified new cell extrinsic roles for epithelial Fra1 to act as an organizer of a microenvironment that fosters ADM. Together, our central hypothesis is that oncogenic ADM features central mediators distinct from those in adaptive ADM that drive subsequent inflammatory and preneoplastic states. Our collaborative teams (Rustgi-Columbia, NYC and Chandwani-Weill Cornell, NYC) will pursue the following interrelated Specific Aims: (1) Define the role of Fra-1 (cell intrinsic) in mediating the switch from adaptive to oncogenic ADM; (2) Delineate how coordinate activation of Prrx1 and Sox9 controls acinar cell responses in ADM; (3) Determine the cell-extrinsic effect(s) of Fra-1 in organizing an ADM-promoting microenvironment. Together, our innovative studies now focus on three specific aspects of the ADM process – Prrx1-Sox9 activation, Fra1 dependency, and microenvironment contributions -- –– that will further illuminate the key biological processes that ensure an appropriate response to tissue-level injury in the pancreas.