Pollin, Gareth

Background/Objectives: Pancreatic ductal adenocarcinoma (PDAC) arises predominantly from activating KRAS mutations, yet individual genetic variants differ markedly in signaling output and clinical impact. G12D, the most prevalent variant, strongly drives oncogenic programs, whereas G12R signals less efficiently through the AKT and ERK pathways and is associated with longer patient survival than G12D-driven PDAC. Methods: To elucidate how these differences influence early cellular transformation, we expressed a panel of KRAS mutants in non-cancerous pancreatic ductal epithelial cells as a model of early PDAC initiation and profiled transcriptional and phospho-proteomic responses. We next examined whether epigenetic differences translate into mutation-specific changes in nuclear organization using quantitative imaging of G12D- and G12R-expressing nuclei at 24 and 48 h. Results: Each variant established a unique regulatory program enriched for chromatin remodelers, histone modifiers, and nuclear structural factors, indicating that variant-specific KRAS signaling rapidly develops divergent epigenetic states. Integrated transcriptomic and phospho-proteomic analyses identified G12D and G12R as the most divergent variants. G12D induced pronounced nuclear remodeling, including increased nuclear size, irregular morphology, and reorganization of the nucleolus and spliceosome, consistent with extensive chromatin and transcriptional reprogramming. In contrast, G12R elicited a weaker response, with minimal or delayed structural changes. Conclusions: Together, these findings demonstrate that KRAS mutational context in pancreatic ductal epithelial cells shapes early transcriptional reprogramming that actively remodels nuclear architecture and nuclear sub-compartments. This work establishes nuclear structural remodeling as a structural state of KRAS-driven epigenetic dysregulation during PDAC initiation.

Abstract Histone H3 lysine 9 methylation (H3K9me), which is written by the Euchromatic Histone Lysine Methyltransferases EHMT1 and EHMT2 and read by the heterochromatin protein 1 (HP1) chromobox (CBX) protein family, is dysregulated in many types of cancers. Approaches to inhibit regulators of this pathway are currently being evaluated for therapeutic purposes. Thus, knowledge of the complexes supporting the function of these writers and readers during the process of cell proliferation is critical for our understanding of their role in carcinogenesis. Here, we immunopurified each of these proteins and used mass spectrometry to define their associated non-histone proteins, individually and at two different phases of the cell cycle, namely G1/S and G2/M. Our findings identify novel binding proteins for these writers and readers, as well as corroborate known interactors, to show the formation of distinct protein complex networks in a cell cycle phase-specific manner. Furthermore, there is an organizational switch between cell cycle phases for interactions among specific writer–reader pairs. Through a multi-tiered bioinformatics-based approach, we reveal that many interacting proteins exhibit histone mimicry, based on an H3K9-like linear motif. Gene ontology analyses, pathway enrichment, and network reconstruction inferred that these comprehensive EHMT and CBX-associated interacting protein networks participate in various functions, including transcription, DNA repair, splicing, and membrane disassembly. Combined, our data reveals novel complexes that provide insight into key functions of cell cycle-associated epigenomic processes that are highly relevant for better understanding these chromatin-modifying proteins during cell cycle and carcinogenesis.