N-Methyladenosine Directly Regulates CD40L Expression in CD4 T Lymphocytes.

T cell activation is a highly regulated process, modulated via the expression of various immune regulatory proteins including cytokines, surface receptors and co-stimulatory proteins. N-methyladenosine (mA) is an RNA modification that can directly regulate RNA expression levels and it is associated with various biological processes. However, the function of mA in T cell activation remains incompletely understood. We identify mA as a novel regulator of the expression of the CD40 ligand (CD40L) in human CD4 lymphocytes. Manipulation of the mA 'eraser' fat mass and obesity-associated protein (FTO) and mA 'writer' protein methyltransferase-like 3 (METTL3) directly affects the expression of CD40L. The mA 'reader' protein YT521-B homology domain family-2 (YTHDF2) is hypothesized to be able to recognize and bind mA specific sequences on the mRNA and promotes its degradation. This study demonstrates that CD40L expression in human primary CD4 T lymphocytes is regulated via mA modifications, elucidating a new regulatory mechanism in CD4 T cell activation that could possibly be leveraged in the future to modulate T cell responses in patients with immune-related diseases.