The TGF-β-inducible miR-23a cluster attenuates IFN-γ levels and antigen-specific cytotoxicity in human CD8+ T cells

Cytokine secretion and degranulation represent key components of CD8(+) T-cell cytotoxicity. While transcriptional blockade of IFN- and inhibition of degranulation by TGF- are well established, we wondered whether TGF- could also induce immune-regulatory miRNAs in human CD8(+) T cells. We used miRNA microarrays and high-throughput sequencing in combination with qRT-PCR and found that TGF- promotes expression of the miR-23a cluster in human CD8(+) T cells. Likewise, TGF- up-regulated expression of the cluster in CD8(+) T cells from wild-type mice, but not in cells from mice with tissue-specific expression of a dominant-negative TGF- type II receptor. Reporter gene assays including site mutations confirmed that miR-23a specifically targets the 3UTR of CD107a/LAMP1 mRNA, whereas the further miRNAs expressed in this clusternamely, miR-27a and -24target the 3UTR of IFN- mRNA. Upon modulation of the miR-23a cluster by the respective miRNA antagomirs and mimics, we observed significant changes in IFN- expression, but only slight effects on CD107a/LAMP1 expression. Still, overexpression of the cluster attenuated the cytotoxic activity of antigen-specific CD8(+) T cells. These functional data thus reveal that the miR-23a cluster not only is induced by TGF-, but also exerts a suppressive effect on CD8(+) T-cell effector functions, even in the absence of TGF- signaling.