T cell receptor associated transmembrane adaptor 1 (TRAT1) modulates human Th17 and Treg responses via PI3-kinase and STAT dependent mechanisms
- Cell Commun Signal. 2025 Oct 10;23(1):431. doi: 10.1186/s12964-025-02429-z.
- 1. Department of Laboratory Medicine, Medical University of Vienna, Vienna, Austria.
- 2. Department of Internal Medicine III, Division of Nephrology and Dialysis, Medical University of Vienna, Vienna, Austria.
- 3. Department of Dermatology, Medical University of Vienna, Vienna, Austria.
- 4. CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna, Austria.
- 5. Department of Otorhinolaryngology, Medical University of Vienna, Vienna, Austria.
- 6. Department of Laboratory Medicine, Medical University of Vienna, Vienna, Austria. [email protected].
- # Contributed equally.
Background: Adaptor proteins associated with the T cell receptor (TCR) play critical roles in regulating immune responses by Translating receptor engagement into intracellular signals. T cell Receptor Associated Transmembrane Adaptor 1 (TRAT1) has been implicated in modulating TCR complex stability, but its functional role in human effector and regulatory CD4⁺ T cell subsets remains poorly understood. This study aimed to elucidate the role of TRAT1 in regulating T cell activation and differentiation, particularly in helper T cells function and regulatory T cells.
Methods: Primary human CD4⁺ T cells, including thymus-derived and induced regulatory T cells (Treg), were genetically modified by CRISPR/Cas9-mediated gene deletion or retro-/lentiviral overexpression of TRAT1. Functional assays, flow cytometry, cytokine quantification, and RNA Sequencing were performed to evaluate modulation of T cell functions. Mechanistic studies included pathway inhibition using small molecules and phospho-protein analysis. The influence of TRAT1 on Treg function was further assessed in a CAR Treg context in an immune Organoid model of allo-rejection.
Results: Thymus-derived, TGFb-induced and FOXP3-transgenic Treg displayed reduced expression of TRAT1 compared to effector T cells, which showed pronounced up-regulation of TRAT1 following activation. In effector T cells, deletion of TRAT1 led to increased signaling through the phosphoinositide 3-kinase pathway resulting in enhanced proliferation and increased expression of activation markers. However, this was accompanied by reduced production of interleukin-17, which was linked to elevated activity of STAT6 as shown by inhibition experiments using small molecule inhibitors. Overexpression and CRISPR/Cas9-mediated knockout of TRAT1 in Treg enhanced suppression of CD4⁺ target cells via up-regulation of LAP/GARP but reduced suppression of CD8⁺ target cells, an effect confirmed in HLA-A2-specific CAR Treg in a human Organoid model of allo-rejection.
Conclusions: TRAT1 acts as a dual regulator of human CD4⁺ T cell function, limiting effector activation through modulation of intracellular signaling and supporting regulatory T cell-mediated suppression. These findings reveal a novel mechanism of immune regulation with potential implications for the development of cell-based immunotherapies.