Abstract A036: <i>Kras</i>-driven proteostatic dysfunction primes pancreatic epithelial cells for tumorigenesis

Abstract Mutations in Kras, the most commonly mutated oncogene in pancreatic ductal adenocarcinoma (PDAC), do not lead to immediate morphological changes in pancreatic acinar cells. In fact, the molecular events driven by Kras that precede and facilitate the earliest transformation towards malignancy, such as acinar-ductal metaplasia (ADM) and PanIN formation, remain unclear. In this study, omics analyses were performed in genetically engineered mouse models to identify and understand cooperating events triggering early metaplasia in PDAC. Mutant Kras transcriptionally downregulates ER-phagy, a selective form of degradation of the endoplasmic reticulum (ER) that involves autophagy-mediated delivery of ER fragments, either defective or that contain aggregated proteins, to the lysosomes. This was not only observed at transcriptional levels in a Kras mutant mouse model of PDAC initiation (KC model), but also using a novel ER-phagy reporter (ss-SRAI-KDEL) where heterogeneous degrees of suppression of ER-phagy across the acinar cell compartment of the KC mouse pancreas were observed, and the areas of greatest downregulation were tightly spatially correlated with incipient ADM. Genetic ablation of ER-phagy by conditional deletion of key ER-phagy gene, Ccpg1, led to homogeneous failure of ER proteostasis across the acinar cell compartment and widespread acceleration of inflammation and ADM in KC mice. Proteomics and high-resolution imaging revealed a small select group of highly aggregation-prone ER luminal proteins that accumulate and aggregate within acinar cells, including the REG3 family of proteins known to be associated with injury. Originally post-translational due to ER-phagy deficiency, the accumulation of aggregation-prone proteins is exacerbated by mutant Kras through a feed-forward transcriptional loop. Crucially, Kras mutation alone is sufficient to drive these protein aggregates in acinar cells over time and this phenotype is tightly spatially associated with the formerly observed suppression of ER-phagy and onset of ADM. Spatial transcriptomics revealed that acinar cells presenting sporadic proteostatic defects were enriched in pancreatic injury associated genes, suggesting this rare population of injured acinar cells is primed for ADM. Additionally, ectopic expression of an aggregation-prone mutant of REG3B in KC mice demonstrated that aggregate formation alone is sufficient to trigger this ADM-primed state and co-operate with Kras. Taken together, these results suggest that ER proteostasis failure and protein aggregation induce inflammation and acinar cell injury predisposing these cells to undergo ADM. Thus, loss of proteostasis and sporadic pathologic protein aggregates are mechanistic hallmarks of early steps in Kras-driven tumorigenesis in PDAC. Citation Format: Carla Salomo Coll, Marisa di Monaco, Jocelyn Holkham, Matt Smith, Morwenna Muir, Philippe Gautier, Hywel Dunn-Davies, Xiaozhong Zheng, Roopesh Krishnankutty, Alain J. Kemp, Katie Winnington-Ingram, Alex von Kriegsheim, Jennifer P. Morton, Natalia Jimenez-Moreno, Damian Mole, Simon Wilkinson. Kras-driven proteostatic dysfunction primes pancreatic epithelial cells for tumorigenesis [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Pancreatic Cancer Research—Emerging Science Driving Transformative Solutions; Boston, MA; 2025 Sep 28-Oct 1; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2025;85(18_Suppl_3):Abstract nr A036.