Elucidating the role of IFT20-TSG101 axis in the initiation of c-SMAC formation in CD4+ T cells

Abstract

$CD4^+$ T cells play a role in the conductor of the adaptive immune system. When $CD4^+$ T cells are activated by antigen recognition, co-stimulation, and cytokines, they orchestrate the detailed immune response by controlling surrounding immune cells such as $CD8^+$ T cells, neutrophils, and eosinophils. Recent literature has highlighted that the formation of supramolecular activation cluster (SMAC), a large ‘immunological synapse’ composed of various signaling complexes, enhances $CD4^+$ T cell activation. The structure of SMAC is similar to a bull’s eye and consists of three concentric circles: (a) central SMAC (c-SMAC), containing the TCR/CD3 complex and CD28, (b) peripheral SMAC (p-SMAC), which contains adhesion molecules, such as integrin-related proteins, and (c) distal SMAC (d-SMAC), composed of CD43 and CD45. Critically, although the composition of SMAC is known, the proteins involved in SMAC formation have not been fully investigated. Surprisingly, single-cell RNA sequencing data showed that intraflagellar transport 20 (IFT20), which is a transporter protein associated with the formation of cilia, was upregulated in stimulated CD4+ T cells with anti-CD3 and anti-CD28 relative to unstimulated CD4+ T cell. We first revealed the protein-protein interaction with IFT20 and tumor susceptibility gene 101 (TSG101), which is essential for the initiation of c-SMAC formation. Formation of c-SMAC by the interaction with TSG101 and IFT20 enhanced the phosphorylation of AKT-mTOR signaling and modulated aerobic glycolysis and cellular respiration through regulation of glucose transporter 1 (GLUT1). Conversely, IFT20-deficient $CD4^+$ T cells showed impaired AKT–mTOR signaling and reduced glucose metabolism, resulting in downregulation of $CD4^+$ T cell effector function. We found that $CD4^+$ T cells from asthma patients showed increased IFT20 expression, whereas mice lacking $CD4^+$ T cell-specific IFT20 displayed reduced protease-induced airway inflammation. In this study, we suggest that TSG101-IFT20 axis initiates c-SMAC formation resulting in enhancement of AKT-mTOR signaling.