PROJECT SUMMARY Pancreatic cancer is a near universally fatal disease with a 5-year survival rate of less than 9%. As the third leading cause of cancer-related deaths in the United States, pancreatic cancer is a major public health concern, necessitating significant advances in our understanding of the underlying disease etiologies. Substantial evidence has recognized inflammation’s role in destabilizing tissue homeostasis. In the pancreas, inflammation manifests as a transient cell-fate transition known as acinar-to-ductal metaplasia (ADM), which is known to play varying roles in both tumor initiation and progression. However, much is still to be learned about how ADM and inflammation—even after subsequent resolution—can lead to the accumulation of molecular changes that aid in pancreatic cancer initiation. Interestingly, we have found that following pancreatitis, acinar cells carry chromatin accessibility changes that persist even eighteen-weeks after histologic recovery. Furthermore, we observe that following resolution of pancreatitis, the persisting inflammatory memory synergizes with either a secondary, sub- threshold non-inflammatory stimulus or oncogenic stress to induce either promiscuous ADM induction or pancreatic tumorigenesis, respectively. Acinar cells thus fail to fully differentiate, and maintain a ‘memory’ of the cycle of metaplasia and regeneration, lowering the threshold for dedifferentiation and tumorigenesis. Motif analysis demonstrates the enrichment of AP-1 motifs at these memory regions—a transcriptional effector activated downstream of the Ras/MAPK pathway. In addition, our preliminary data demonstrates that the acinar population responds heterogeneously to inflammation-associated injury—with both an ADM-permissive and an ADM-resistant population co-occurring during pancreatitis. Given these findings, we hypothesize that AP- 1/Fra1 promotes inflammatory memory formation and tumorigenesis in a subset of pancreatic acinar cells permissive to metaplastic transition. In the proposed studies, we set out to determine if AP-1/Fra1 is responsible for memory formation, promiscuous ADM induction, and tumor initiation. Additionally, the proposed studies serve to identify the cellular dynamics associated with metaplastic transition, the distribution of the memory in ADM-permissive and -resistant populations, as well as the increased susceptibility of ADM-permissive cells to malignant transformation. To address the functional role of Fra1, we will utilize complementary 2D/3D in vitro systems and in vivo models of Fra1 deletion and AP-1 inhibition. To determine the molecular characteristics, dynamics, and tumorigenic outcomes associated with the divergent cell fate decisions, we will employ distinct lineage tracing mouse models that conditionally mark cells and reversibly induce mutant Kras in the pancreas. We anticipate that a better understanding of these processes will further elaborate on the connection between inflammation and onc...