Abstract LB263: An in vivo unbiased screen identifies clathrin adaptor protein complex-2 as a novel tumor suppressor

Abstract

Abstract Pancreatic ductal adenocarcinoma (PDAC) is almost uniformly lethal. It is thus imperative to find new therapeutic approaches to treat this disease. While whole genome CRISPR/Cas9 screens have successfully identified new vulnerabilities in PDAC cell lines, it is becoming increasingly clear that cell culture do not faithfully recapitulate the complex nature of tumorigenesis in vivo, and hence may fail to identify the full spectrum of potential therapeutic targets to be explored in this devastating disease. As previous screens we performed identified phosphatidylinositol (Ptdlns) metabolism as important for pancreatic cell growth, I generated a custom sgRNA library targeting this entire form of metabolism. To identify vulnerabilities specific to tumor growth, I screened this library in five different human PDAC cell lines grown in culture versus as xenograft tumors. I found that sgRNAs targeting two genes encoding separate subunits of the Adaptor Protein complex-2 (AP2), a regulator of clathrin mediated endocytosis, were negatively enriched in all five PDAC cell lines when grown in culture. In agreement, AP2 subunit genes are considered common essential by DepMap. Paradoxically however, the same sgRNAs were positively enriched in three of these five cell lines when grown as xenograft tumors. This begs the question how the loss of a supposably essential complex behaves like a tumor suppressor and instead enhances tumor growth when disrupted. Here, I will present data that loss of AP2 results in a substantial restructuring the plasma membrane proteome, which in cultured cells results in the loss of iron transport, one of the main functions of this complex, and cell death. Conversely, this restructuring in vivo retains receptors and adhesion proteins on the cell surface, where transcriptome and proteomic analysis indicate enhances proliferative signaling. These data support AP2 promoting cell viability of cultured cells through active iron transport, but suppresses tumor growth in vivo by endocytosing the very receptors needed for tumor growth. Citation Format: Seth Parker Zimmerman, Christopher M. Counter. An in vivo unbiased screen identifies clathrin adaptor protein complex-2 as a novel tumor suppressor [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB263.