CTLA-4-targeted proteins in differentiating CD8+ T lymphocytes

Abstract

Abstract The blockade of inhibitory receptors like Cytotoxic T Lymphocyte-associated molecule-4 (CTLA-4, CD152) on T cells is a potent approach to regain functionality of ineffective immune responses against tumor cells. However, the underlying mechanisms of CTLA-4 mediated attenuation in CD8+ T cells are still incompletely explored. To discover proteins targeted by CTLA-4, we used a CD8+ T cell in vitro activation system combined with iTRAQ proteomic analysis. The mass spectrometry data revealed that CTLA-4-controls central changes in phosphorylation of proteins involved in T cell signaling, RNA processing, DNA replication and microtubule polymerization. Beside other molecules, we identified and verified CTLA-4-mediated post-translational modifications of the AP-1 family transcription factor Fos-related antigen 2 (Fra-2) as well as the regulation of an inhibitor of protein translation and set up a network of proteins altered by CTLA-4. Consequently, CD8+ T cells deficient for CTLA-4-induced targets showed enhanced production of otherwise repressed effector molecules like IFN-gamma and Granzyme B and ultimately proofed to be superior in control of tumor growth. These findings delineate how CTLA-4 is able to modulate CD8+ T cell differentiation and provide new strategies to improve anti-tumor immune therapy.