Liver X receptor activation in chronic myelogenous leukemia cells yields distinct mass fingerprints by whole cell MALDI-TOF MS, which correspond to changes in cell viability, gene expression, and differentiation markers

Abstract

Liver X receptor (LXR) agonists, including synthetic ligands or naturally-occurring oxysterols, exert promising lipid-modulating, anti-inflammatory, and anti-tumor effects. Matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) whole cell mass spectrometry (MS) shows promise in chronic disease and food science research, clinical diagnostics of cancer cells and bacterial pathogens, and drug/nutraceutical discovery due to its relatively low-cost, rapid, reliable, and high-throughput ability to identify unique cell phenotypes and differentiation states of immune cells that play essential roles in chronic metabolic and inflammatory disease pathophysiology. However, optimization of whole cell MALDI-TOF MS-based methods to assess cellular changes in response to pharmaceutical and/or nutraceutical treatment warrants further study. Thus, we investigated whether whole cell MALDI-TOF MS could detect cellular phenotype changes of human stem-like erythroleukemia K562 cells – a model for chronic myelogenous leukemia (CML) – induced by the LXR agonist TO-901317, a synthetic ligand that mimics effects of naturally-occurring oxysterols, which are oxidized cholesterol derivatives formed under conditions of high cellular cholesterol concentrations and in food products. TO-901317 dose- and time-dependently altered mRNA expression of cholesterol flux genes, including ATP-binding cassette transporter A1 (ABCA1), LDL-receptor (LDLR), HMG-CoA reductase (HMGCR), and reduced cellular cholesterol content by 22.9% at 24 hours. TO-901317 additionally dose- and time-dependently impacted K562 cell viability, number, size, and reduced mRNA expression of the anti-apoptotic gene BCL2L1 by 43.3%. These effects corresponded to induced gene expression of erythroid markers and hemoglobin content, suggesting that LXR activation may promote erythroid lineage differentiation. Whole cell MALDI-TOF MS mass fingerprinting revealed distinct proteomic phenotypes between TO-901317 vs. untreated cells, and identified histone 2A and histone H4 as uniquely expressed proteins. These findings not only elucidate a novel role for LXR agonists in a model of CML, but demonstrate that mass fingerprints obtained by whole cell MALDI-TOF mass spectrometry effectively distinguish between treatment-induced cell phenotypes.