The Proceedings of the National Academy of Sciences (PNAS) published online a research paper titled "AMBRA1 controls the translation of immune-specific genes in T lymphocytes" by the research group of Yikun Yao from the Shanghai Institute of Nutrition and Health, Chinese Academy of Sciences. This study screened and identified the key regulatory protein AMBRA1 in the FAS-mediated T cell death process, revealing a new mechanism by which AMBRA1 controls TCR signaling, T cell cycle and T cell death at the translation level.
Figure 1. A new mechanism of AMBRA1 controlling TCR signaling, T cell cycle and T cell death at the translation level. (Gottlieb S, et al., 2024)
After antigen stimulation of T cell receptors, T cells are rapidly activated and differentiated into effector T cells or memory T cells. Activated T cells quickly start glycolysis to produce energy and essential components to promote T cell proliferation, and in this process T cells need to quickly synthesize a large amount of protein. Therefore, in addition to transcriptional regulation, efficient translational regulation may also play an important role in T cell activation. Previously, research on T cell activation and activation-induced T cell death focused on regulation at the transcriptional level of T cells, while research on the translation level of T cells was insufficient.
To reveal new regulatory factors that mediate T cell death, this study used whole-genome CRISPR library screening and found that the scaffold protein AMBRA1 plays an important role in FAS-mediated T cell death. AMBRA1 protein is a phylogenetically conserved scaffold protein. Previous studies have shown that AMBRA1 is a key regulator of autophagy, E3 ubiquitin ligase activity and cell cycle proteins, but there have been no reports on the function of AMBRA1 in lymphocytes and its translation-related regulatory mechanisms.
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This study used flow cytometry, immunoblotting, and a series of functional experiments to verify that knocking out AMBRA1 can reduce FAS protein expression and inhibit T cell apoptosis induced by the FAS pathway. Further, in the mechanism exploration, the researchers used OPP incorporation combined with click chemistry, sucrose gradient centrifugation to separate ribosomes and their bound mRNA, and found that AMBRA1 promotes FAS mRNA translation, and this regulatory effect is essential for the complete expression of FAS after T cell activation.
This study found that TCR signals can stimulate increased AMBRA1 expression through RNA-seq and mass spectrometry results. Then, using TCR downstream pathway inhibitors and AMBRA1 5'UTR reporter genes, the TCR stimulation-induced translation control pathway was discovered. This translation control pathway can enhance AMBRA1 translation through the CD28-PI3K-mTORC1-eIF4F axis after T cell activation, and regulate the expression of FAS and other immune-related genes.
Furthermore, researchers used a series of protein interaction and translation level detection technologies such as Bio-ID, SunSET, SILAC and combined with mePROD to find that AMBRA1 interacts with multiple ribosomal proteins and promotes the translation of multiple ribosomal biosynthesis-related proteins. Whole proteomics analysis and other experiments showed that in addition to FAS, the protein translation of more TCR signaling genes such as CD69, CD28, PD1 and CTLA4 is also regulated by AMBRA1, indicating that AMBRA1 has a wide range of effects on the translation of T cell signaling proteins.
This study discovered the role of the AMBRA1 gene in the translational regulation of TCR activation and FAS-induced T cell death signals, providing a possible direction for exploring the translational regulation of TCR signals and developing immunotherapies targeting translational regulation.
Reference
Gottlieb S, et al. AMBRA1 controls the translation of immune-specific genes in T lymphocytes. Proceedings of the National Academy of Sciences, 2024, 121(44): e2416722121.