Arthritis suppressor genes TIA-1 and TTP dampen the expression of tumor necrosis factor alpha, cyclooxygenase 2, and inflammatory arthritis.

TIA-1 and TTP are AU-rich element-binding proteins that prevent the pathological overexpression of tumor necrosis factor alpha (TNF-alpha). TIA-1 inhibits the translation of TNF-alpha transcripts, whereas TTP promotes the degradation of TNF-alpha transcripts. Here we show that TIA-1 and TTP function as arthritis suppressor genes: TIA-1(-/-) mice develop mild arthritis, TTP(-/-) mice develop severe arthritis, and TIA-1(-/-)TTP(-/-) mice develop very severe arthritis. Peritoneal macrophages derived from all three genotypes overexpress cyclooxygenase 2 and TNF-alpha. Surprisingly, lipopolysaccharide-activated TIA-1(-/-)TTP(-/-) macrophages secrete less TNF-alpha protein than either TIA-1(-/-) or TTP(-/-) macrophages. In these mice, arthritogenic cytokine may be produced by neutrophils that accumulate in the bone marrow and peripheral blood. Our results suggest that TIA-1 and TTP are genetic modifiers of inflammatory arthritis that can alter the spectrum of cells that produce arthritogenic cytokines.