FAT10 is phosphorylated by IKKβ to inhibit the antiviral type-I interferon response.

IFN-I secretion provides a rapid host defense against infection with RNA viruses. Within the host cell, viral RNA triggers the activation of the RIG-I signaling pathway, leading to the production of IFN-I. Because an exaggerated IFN-I response causes severe tissue damage, RIG-I signaling is tightly regulated.

Regulation of Interferon Induction by the Ubiquitin-Like Modifier FAT10.

The revelation that the human major histocompatibility complex (MHC) class I locus encodes a ubiquitin-like protein designated HLA-F adjacent transcript 10 (FAT10) or ubiquitin D (UBD) has attracted increasing attention to the function of this protein. Interestingly, the pro-inflammatory cytokines interferon (IFN)-γ and tumor necrosis factor (TNF) α synergize to strongly induce FAT10 expression, thereby suggesting a role of FAT10 in the immune response. Recent reports that FAT10 downregulates type I interferon production while it upregulates IFN-γ pose mechanistic questions on how FAT10 differentially regulates interferon induction.

The ubiquitin-like modifier FAT10 is required for normal IFN-γ production by activated CD8 T cells.

FAT10 is the only ubiquitin-like modifier which directly targets its substrate proteins for rapid degradation by the proteasome. While the conjugation and proteasomal targeting of FAT10 are fairly well understood, the biological functions of FAT10 have remained largely elusive. Here we have investigated the role of FAT10 in cytokine responses in mice upon viral infection.

The expression profile of the ubiquitin-like modifier FAT10 in immune cells suggests cell type-specific functions.

The TNF and IFN-γ-inducible ubiquitin-like modifier HLA-F adjacent transcript 10 (FAT10) is most prominently expressed in immunological tissues but information regarding basal expression and inducibility of FAT10 in the different types of immune cells is still lacking. Hence, we investigated FAT10 mRNA expression in the major human and murine immune cell subsets, and FAT10 protein expression in human leukocytes. We isolated the different human leukocytes from peripheral blood and the murine immune cell subsets from spleen.