Abstract A087: Loss of KDM5A supports KRAS-driven pancreatic cancer
Authors: Chen Jasper , Han Jincheng , DePinho Ronald A. , Taniguchi Cullen M. 
Published: January 2024

Abstract
Objective: Our objective is to investigate the potential link between the Kras and hypoxia in pancreatic ductal adenocarcinoma (PDAC). PDAC is notorious for its resistance to chemotherapy, radiotherapy, and immunotherapy, owing to its dense stroma and high intratumoral hypoxia. Here, we explore how loss of Kdm5a reprograms the epigenome and contributes to Kras-driven pathology in PDAC. We believe that loss of Kdm5a plays an essential role in enabling cancer cells to survive under hypoxic conditions. Methods: We used cell lines (iKPCs) derived from a genetically engineered mouse model of PDAC with doxycycline-inducible KrasG12D. To induce KrasG12D expression, cells were cultured in media containing 1 mcg/ml doxycycline (Kras-on). To turn off KrasG12D expression, cells were cultured in tetracycline-free media (Kras-off). Pharmaceutical inhibition of KrasG12D, MEK, and ERK was performed by treating iKPCs with MRTX-1133, mirdametinib, and ravoxertinib, respectively. MG-132 was used to inhibit the proteasome pathway. Kdm5a was overexpressed in iKPCs by lentiviral infection. Profiling of histone modifications was performed by epiproteomic mass spectrometry of iKPCs under three conditions: Kras-off, Kras-on, and Kras-on overexpressing Kdm5a. Results: The induction of oncogenic Kras led to a decrease in Kdm5a protein levels, which was restored by reduced oncogenic Kras expression induced by doxycycline withdrawal or Kras-specific inhibition with MRTX-1133. Proteasomal inhibition using MG-132 also stabilized Kdm5a. This suggests that phosphorylation of Kdm5a by Erk may lead to activation of a phosphodegron, ubiquitination, and subsequent proteasomal degradation. Immunoprecipitation of Kdm5a confirmed elevated phosphorylated-Ser/Thr and ubiquitin in the Kras-on condition. Although Kdm5a is a H3K4me3 demethylase, we observed no differences in the total abundance of H3K4me3 in the conditions we profiled. Conversely, acetylation of several histone marks, including H3K14ac and H4K16ac, were elevated in Kras-off compared to Kras-on iKPCs. The overexpression of Kdm5a in Kras-on iKPCs was found to rescue the reduction in histone acetylation. Conclusions: We present compelling evidence that oncogenic Kras induces the proteasomal degradation of Kdm5a in PDAC. Restoring Kdm5a in PDAC mitigates some epigenetic alterations induced by Kras. Our research unearths a hitherto unexplored pathway through which Kras can reprogram the epigenome. Although mass spectrometry studies of Kdm5a have previously found that it could interact with subunits of histone acetyltransferase (HAT) complexes, including Tip60 and Mrg15, direct evidence that Kdm5a facilitates histone acetylation has not been described. Thus, our findings could broaden understanding for predicting and identifying potential escape mechanisms that could arise upon Kras inhibition before they manifest in patients, providing a more proactive approach to managing PDAC.
Citation Format: Jasper Chen, Jincheng Han, Ronald A. DePinho, Cullen M. Taniguchi. Loss of KDM5A supports KRAS-driven pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Pancreatic Cancer; 2023 Sep 27-30; Boston, Massachusetts. Philadelphia (PA): AACR; Cancer Res 2024;84(2 Suppl):Abstract nr A087.