Abstract B079: Unfolding the role of cell state on stress granule heterogeneity and function in pancreatic cancer

Abstract

Abstract Phenotypic and functional heterogeneity is a common feature of cancer cells that poses as a major therapeutic challenge. Previous work has implicated the phase-separation organelles, stress granules (SGs), as important mediators of tumorigenesis that function as a mutant KRAS-driven stress-adaptive mechanism to enhance cellular fitness. We have found that mutant KRAS pancreatic cancer cells show a high degree of intra-cellular heterogeneity in SG formation, ranging from no SGs to markedly high levels. Given the function of SGs in cancer cell fitness and the role of cancer cell heterogeneity in tumor progression and therapeutic response, we sought to understand the determinants of SG heterogeneity and its role in KRAS-driven tumorigenesis. Here, we show that the capability of KRAS mutant pancreatic cancer cells to form SGs is dependent on the cell cycle state, with cells in G2 phase showing markedly enhanced SG formation. We demonstrate that this heterogeneity in SG formation is determined by a cell cycle specific interplay between the activator of cell death, Caspase 3, and the SG regulator molecule 15-deoxy-delta-12,14-prostaglandin J2 (15-d-PGJ2). We show that 15-d-PGJ2 production in G2 is driven by calcium-dependent phospholipase A2 (cPLA2) activity and is subject to regulation by Caspase 3. Our results show that the capacity of Caspase 3 to cleave and inactivate the cPLA2 protein is specifically suppressed in G2, thus leading to upregulation of cPLA2 activity and 15-d-PGJ2 levels. As such, we find that 15d-PGJ2 levels are highest in G2 and that the inhibition of cPLA2 blocks SG formation in G2 specifically. Accordingly, exogenous 15d-PGJ2 rescues SG formation in cPLA2-inhibited G2 cells. In addition, we demonstrate that Caspase 3 inhibition increases 15-d-PGJ2 levels and stimulates SG formation in asynchronous cells, mirroring the natural suppression of Caspase 3 seen in G2. Importantly, we show that heterogeneity in SG levels translates into a functional heterogeneity whereby SG inhibition preferentially sensitizes cells in G2 to stress stimuli. Altogether these data support a model whereby SG formation integrates cues from cell death and proliferative signals and indicate that SG levels may be critical to achieve a clear signal for cell cycle progression at the G2/M border. Furthermore, our findings suggest that cancer cells may show differential sensitivity to anti-SG therapy as they progress through the cell cycle, and pairing such therapy with G2-synchronizing chemotherapeutics may increase susceptibility and thus treatment efficacy. Citation Format: Alexandra Redding, Guillaume Fonteneau, Elda Grabocka. Unfolding the role of cell state on stress granule heterogeneity and function in pancreatic cancer [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer; 2022 Sep 13-16; Boston, MA. Philadelphia (PA): AACR; Cancer Res 2022;82(22 Suppl):Abstract nr B079.