Abstract 4757: Loss of KDM5A supports KRAS-driven pancreatic cancer

Objective: Mutant KRAS is a primary driver of pancreatic ductal adenocarcinoma (PDAC), which exhibits marked hypoxia. Despite the strong association of hypoxia and PDAC, the relationship between KRAS and hypoxia is still poorly understood. The oxygen-sensitive histone lysine demethylase, KDM5A, was recently reported to mediate epigenetic responses to hypoxia independent of the hypoxia-inducible factors. KDM5A epigenetically represses transcription via two mechanisms: by its demethylase activity on activating H3K4me3 marks, and through its interaction with deacetylase complexes containing HDAC1/2, which deacetylates activating H3K9ac and H4K16ac histone marks. Under hypoxic conditions, KDM5A loses its activity, leading to restoration of these H3K4me3 marks, thereby activating KDM5A target genes. The purpose of this study is to understand how KDM5A loss of function contributes to pathogenesis of mutant KRAS-driven pancreatic cancer. Methods: Cell lines derived from mice with pancreas-specific p53 deletion and doxycycline-inducible expression of KrasG12D (iKPC). Protein lysates were prepared using RIPA buffer. Histones were purified by acid extraction. Immunoblotting was used to probe for protein levels of Kdm5a, H3K4me3, H3K9ac, and H4K16ac. Genetic ablation of KrasG12D was performed by culturing iKPCs in tetracycline-free medium. Kras was induced by adding doxycycline to the culture medium. Pharmaceutical inhibition of MEK, proteasome, and Kdm5a were performed by treating iKPCs with mirdametinib, MG-132, and CPI-455, respectively. Knockdown of β-TrCP and FBXW7 were performed by stable expression of shRNA in iKPCs. Protein motif scanning was performed using the Eukaryotic Linear Motif (ELM) Prediction online software. Results: We discovered that Kdm5a protein levels were abrogated by induction of KrasG12D and stabilized by genetic ablation of Kras. Pharmaceutical inhibition of MEK or proteasome function stabilized Kdm5a, indicating that Kras induces Kdm5a proteasomal degradation through the MEK/ERK pathway. H3K4me3, H3K9ac, and H4K16ac histone marks were increased in Kras-on iKPC compared to Kras-off iKPC, consistent the expected effect of Kras-induced Kdm5a degradation. Pharmaceutical inhibition Kdm5a in the Kras-off setting restored H3K4me3, suggesting that Kdm5a contributes to demethylation of H3K4me3 in iKPC. We identified two phosphodegron sites corresponding to β-TrCP and FBXW7 of the ubiquitin ligase complex within the Kdm5a protein sequence. Knockdow