癌症生物学

Stable isotopes have frequently been used to study metabolic processes in live cells both in vitro and in vivo. Glutamine, the most abundant amino acid in human blood, plays multiple roles in cellular metabolism by contributing to the production of nucleotides, lipids, glutathione, and other amino acids. It also supports energy production via anaplerosis of tricarboxylic acid cycle intermediates. While ¹³C-glutamine has been extensively employed to study glutamine metabolism in various cell types, detailed analyses of specific lipids derived from ¹³C-glutamine via the reductive carboxylation pathway are limited. In this protocol, we present a detailed procedure to investigate glutamine metabolism in human glioblastoma (GBM) cells by conducting ¹³C-glutamine tracing coupled with untargeted metabolomics analysis using liquid chromatography–mass spectrometry (LC–MS/MS). The method includes step-by-step instructions for the extraction and detection of polar metabolites and long-chain fatty acids (LCFAs) derived from ¹³C-glutamine in GBM cells. Notably, this approach enables the distinction between isomers of two monounsaturated FAs with identical masses: palmitoleic acid (16:1n-7) (cis-9-hexadecenoic acid) and palmitelaidic acid (16:1n-7) (trans-9-hexadecenoic acid) derived from ¹³C-glutamine through the reductive carboxylation process. In addition, using this protocol, we also unveil previously unknown metabolic alterations in GBM cells following lysosome inhibition by the antipsychotic drug pimozide.

Laser-assisted microdissection (LAM) coupled with next-generation sequencing technologies offers a powerful approach to dissecting the complex cellular heterogeneity within lung adenocarcinoma (LUAD) tumors. This protocol outlines the method for isolating specific high-risk LUAD tissues containing micropapillary/solid (MIP/SOL) patterns, which is linked to poor prognosis. We detail the process of LAM, which involves tissue fixation, microtome sectioning, and the precise dissection and collection of cells of interest under microscopic guidance. The isolated cells are then subjected to RNA extraction, library preparation, and sequencing to profile transfer RNA–derived fragments (tRFs) and tRNA-derived stress-induced RNAs (tiRNAs), which are emerging as key regulators in cancer. This protocol enables researchers to obtain high-quality transcriptomic data from specific LUAD cell populations, aiming to uncover tRF-Val-CAC-024 and tiRNA-Gly-CCC as potential biomarkers for early diagnosis and therapeutic targets for LUAD treatment.

ATAC-seq (assay for transposase-accessible chromatin with high-throughput sequencing) is a powerful method to evaluate chromatin accessibility and nucleosome positioning at a genome-wide scale. This assay uses a hyperactive Tn5 transposase, to simultaneously cut open chromatin and insert adapter sequences. After sequencing, the reads generated through this technique are generally indicative of transcriptional regulatory elements that are located in accessible chromatin. This method was originally developed by Buenrostro et al. (2013), and since then it has been improved by the same authors several times, until their last update called OMNI ATAC-seq (Corces et al., 2017). Here, we describe an ATAC-seq protocol based on the OMNI-ATAC method, with a special focus on the initial steps of thawing cryopreserved cells, and the final steps of library purification using magnetic beads. This protocol can be of interest for laboratories working in a fast-paced environment.

Graphic abstract:

Flowchart of the protocol

Once thought to be a mere consequence of the state of a cell, intermediary metabolism is now recognized as a key regulator of mammalian cell fate and function. In addition, cell metabolism is often disturbed in malignancies such as cancer, and targeting metabolic pathways can provide new therapeutic options. Cell metabolism is mostly studied in cell cultures in vitro, using techniques such as metabolomics, stable isotope tracing, and biochemical assays. Increasing evidence however shows that the metabolic profile of cells is highly dependent on the microenvironment, and metabolic vulnerabilities identified in vitro do not always translate to in vivo settings. Here, we provide a detailed protocol on how to perform in vivo stable isotope tracing in leukemia cells in mice, focusing on glutamine metabolism in acute myeloid leukemia (AML) cells. This method allows studying the metabolic profile of leukemia cells in their native bone marrow niche.

The activation of the Takeda G-protein receptor 5 (TGR5, also known as the G protein-coupled bile acid receptor 1, GPBAR1) in enteroendocrine L-cells results in secretion of the anti-diabetic hormone Glucagon-Like Peptide 1 (GLP-1) into systemic circulation. Consequently, recent research has focused on identification and development of TGR5 agonists as type 2 diabetes therapeutics. However, the clinical application of TGR5 agonists has been hampered by side effects of these compounds that primarily result from their absorption into circulation. Here we describe an in vitro screening protocol to evaluate the TGR5 agonism, GLP-1 secretion, and gut-restricted properties of small molecules. The protocol involves differentiating gut epithelial and endocrine cells together in transwells to assess both the pharmacodynamics of TGR5 agonists and the toxicity of compounds to the intestinal monolayer. As a proof of concept, we demonstrate the use of the protocol in evaluating properties of naturally occurring bile acid metabolites that are potent TGR5 agonists. This protocol is adapted from Chaudhari et al. (2021).

Exosomes and other extracellular vesicles (EVs) are considered the main vehicles transporting RNAs in extracellular samples, including human bodily fluids. However, a major proportion of extracellular RNAs (exRNAs) do not copurify with EVs and remain in ultracentrifugation supernatants of cell-conditioned medium or blood serum. We have observed that nonvesicular exRNA profiles are highly biased toward those RNAs with intrinsic resistance to extracellular ribonucleases. These highly resistant exRNAs are interesting from a biomarker point of view, but are not representative of the actual bulk of RNAs released to the extracellular space. In order to understand exRNA dynamics and capture both stable and unstable RNAs, we developed a method based on size-exclusion chromatography (SEC) fractionation of RNase inhibitor (RI)-treated cell-conditioned medium (RI-SEC-seq). This method has allowed us to identify and study extracellular ribosomes and tRNAs, and offers a dynamical view of the extracellular RNAome which can impact biomarker discovery in the near future.

Graphical abstract:

Overview of the RI-SEC-seq protocol: sequencing of size-exclusion chromatography fractions from nonvesicular extracellular samples treated or not with RNase inhibitors (+/- RI)