TLR8-dependent TNF{alpha} over-expression in Fanconi anemia group C cells. Blood [Blood] Journal article

A Fanconi anemia (FA) protein complex facilitates ubiquitinylation of FANCI and FANCD2. Whether FA sub complexes influence ubiquitinylation of other substrates is unknown. Here we show, using gene expression microarray and proteomics methods, that genes encoding proteins directly involved in ubiquitinylation are over-represented in the signature of FA bone marrow cells and that while some proteins are uniquely ubiquitinylated in complemented cells, others are ubiquitinylated only in mutant cells. One in the latter category was toll-like receptor 8 (TLR8). Because TNFalpha production is abnormally high in FA-C cells and contributes to the pathogenesis of the marrow failure phenotype, we tested the hypothesis that TNFalpha gene over-expression in FA-C cells is TLR8-dependent. We confirmed that TLR8 (or a TLR8-associated protein) is ubiquitinylated in mutant FA-C cells, and that high level TNFalpha synthesis in mutant cells depended upon TLR8 and the canonical downstream signaling intermediates IRAK-1 and IKK-alpha/beta. FANCC deficient THP-1 cells over-expressed TNFalpha in response to TLR8 agonists but not other TLR agonists, and primary splenic macrophages from Fancc(-/-) mice were also hypersensitive to the TLR8 agonist R848. TNFalpha production in FA-C cells was suppressed by inhibitors of TLR8, p38 MAPK, IRAK, and IKK. Engineered point mutations of FANCC were capable of complementing the mitomycin C hypersensitivity phenotype of FANCC mutant cells but did not suppress TNFalpha overproduction. In conclusion, FANCC suppresses production of TNFalpha in mononuclear phagocytes by suppressing TLR8 activity and this function of FANCC is independent of its function in protecting the genome from cross-linking agent-induced damage.

Blood [Blood]