Abstract 5302: Unmasking aggressive tumor profiles in lung adenocarcinomas through the molecular abundances and catalytic action of serine hydrolases
Authors: Sajic Tatjana , Arni Stephan , Aebersold Rudolf , Hillinger Sven 
Published: June 2023

Abstract
(a) Current proteomic methods quantify solely the catalytically active portion of enzymes without normalizing the active portion to the total enzyme amount, thus compromising comparison of the results. We take advantage of a SWATH/DIA-MS workflow and describe a method based on depletion-dependent ABPP (dd-ABPP) able to concurrently determine catalytically active enzymes and their total molecular abundances, as well as quantify the contextual sample proteomes.
(b) We monitored high quality peptides of more than 190 SH activities and molecular abundances of around 4000 contextual tissue proteins in advanced lung adenocarcinomas (LUAD). While we found that LUAD tumors display enhanced proteolytic activities compared with control lung tissue, the most prominent characteristic of an aggressive tumor phenotype was enhanced lipolysis of metabolic SHs emphasized by IAH1, ABHD12, LYPLA2 and ABHD10.
(c) Molecular signatures of the activity profiles of 23 SHs and 59 contextual tissue proteins discriminate aggressive tumors at the time of diagnosis. Enhanced detection of S-palmitoylated proteins correlating by active-enzyme capture uncovers their functional links with the metabolic SHs related to lipoprotein depalmitoylation via enzymes displaying increased de-palmitoylase activities and enhanced fatty acid metabolism in aggressive LUAD. To further validate our findings, we analysed LUAD tumors for panels of saturated and unsaturated fatty acid (C8-C22) levels. Strikingly, we detected a statistically significant increase in monounsaturated palmitoleic acid (C16:1) in the aggressive compared with less-aggressive tumors. Notably, the primary source of palmitoleic acid in the cellular environments results from an excess of free palmitic acid and its conversion by rate-limiting enzyme Stearoyl-CoA desaturase 1 (SCD) that is enhanced in LUAD cancer.
(d) We detected a significant increase in palmitoleic acid levels in aggressive tumors. To a certain extent our data support previous findings on the active process of lipid desaturation in lung adenocarcinoma cells as the main source of energy for cell proliferation. Our approach also revealed that changes in the active lipase fractions between subtypes do not follow changes in enzyme protein quantities, suggesting that lipase regulations are related rather to peculiarities of the enzyme protein sequence, a distorted enzyme-inhibitor equilibrium, or a distorted molecular composition of the tissue itself. Since the inhibitors of serine lipases are promising targets in other RAS-mutant carcinomas, and the inhibitors of a rate-limiting SCD1 enzyme prevent palmitic acid conversion to a monounsaturated form, these metabolic vulnerabilities detected in aggressive LUAD will be helpful for future therapeutic strategies in lung cancer.
Citation Format: Tatjana Sajic, Stephan Arni, Rudolf Aebersold, Sven Hillinger. Unmasking aggressive tumor profiles in lung adenocarcinomas through the molecular abundances and catalytic action of serine hydrolases. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5302.