contributed equally to this work TIA-1 and TIAR are related proteins that bind to an AU-rich element (ARE) in the 3¢ untranslated region of tumor necrosis factor alpha (TNF-a) transcripts. To determine the functional signi®cance of this interaction, we used homologous recombination to produce mutant mice lacking TIA-1. Although lipopolysaccharide (LPS)-stimulated macrophages derived from wild-type and TIA-1 ±/± mice express similar amounts of TNF-a transcripts, macrophages lacking TIA-1 produce signi®cantly more TNF-a protein than wild-type controls. The half-life of TNF-a transcripts is similar in wild-type and TIA-1 ±/± macrophages, indicating that TIA-1 does not regulate transcript stability. Rather, the absence of TIA-1 signi®cantly increases the proportion of TNF-a transcripts that associate with polysomes, suggesting that TIA-1 normally functions as a translational silencer. TIA-1 does not appear to regulate the production of interleukin 1b, granulocyte±macrophage colony-stimulating factor or interferon g, indicating that its effects are, at least partially, transcript speci®c. Mice lacking TIA-1 are hypersensitive to the toxic effects of LPS, indicating that this translational control pathway may regulate the organismal response to microbial stress.

Stress granules (SGs) are dynamic cytoplasmic foci at which stalled translation initiation complexes accumulate in cells subjected to environmental stress. SG-associated proteins such as TIA-1, TIAR and HuR bind to AU-rich element (ARE)-containing mRNAs and control their translation and stability. Here we show that tristetraprolin (TTP), an ARE-binding protein that destabilizes ARE-mRNAs, is recruited to SGs that are assembled in response to FCCP-induced energy deprivation, but not arsenite-induced oxidative stress. Exclusion of TTP from arsenite-induced SGs is a consequence of MAPKAP kinase-2 (MK2)-induced phosphorylation at serines 52 and 178, which promotes the assembly of TTP:14-3-3 complexes. 14-3-3 binding excludes TTP from SGs and inhibits TTP-dependent degradation of ARE-containing transcripts. In activated RAW 264.7 macrophages, endogenous TTP:14-3-3 complexes bind to ARE-RNA. Our data reveal the mechanism by which the p38-MAPK/MK2 kinase cascade inhibits TTP-mediated degradation of ARE-containing transcripts and thereby contributes to lipopolysaccharide-induced TNFalpha expression.

IMPORTANCE Sprifermin is under investigation as a disease-modifying osteoarthritis drug.OBJECTIVE To evaluate the effects of sprifermin on changes in total femorotibial joint cartilage thickness in the more symptomatic knee of patients with osteoarthritis. Osteoarthritis Randomized Trial with Administration of Repeated Doses) was a 5-year, dose-finding, multicenter randomized clinical trial conducted at 10 sites. Eligible participants were aged 40 to 85 years with symptomatic, radiographic knee osteoarthritis and Kellgren-Lawrence grade 2 or 3. Enrollment began in July 2013 and ended in May 2014; the last participant visit occurred on May 8, 2017. The primary outcome at 2 years and a follow-up analysis at 3 years are reported. DESIGN, SETTING, AND PARTICIPANTSINTERVENTIONS Participants were randomized to 1 of 5 groups: intra-articular injections of 100 μg of sprifermin administered every 6 months (n = 110) or every 12 months (n = 110), 30 μg of sprifermin every 6 months (n = 111) or every 12 months (n = 110), or placebo every 6 months (n = 108). Each treatment consisted of weekly injections over 3 weeks. MAIN OUTCOMES AND MEASURESThe primary end point was change in total femorotibial joint cartilage thickness measured by quantitative magnetic resonance imaging at 2 years. The secondary end points (of 15 total) included 2-year change from baseline in total Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores. The minimal clinically important difference (MCID) is unknown for the primary outcome; for total WOMAC score in patients with hip and knee osteoarthritis, the absolute MCID is 7 U (95% CI, 4 to 10 U) and the percentage MCID is 14% (95% CI, 9% to 18%). RESULTS Among 549 participants (median age, 65.0 years; 379 female [69.0%]), 474 (86.3%) completed 2-year follow-up. Compared with placebo, the changes from baseline to 2 years in total femorotibial joint cartilage thickness were 0.05 mm (95% CI, 0.03 to 0.07 mm) for 100 μg of sprifermin administered every 6 months; 0.04 mm (95% CI, 0.02 to 0.06 mm) for 100 μg of sprifermin every 12 months; 0.02 mm (95% CI, −0.01 to 0.04 mm) for 30 μg of sprifermin every 6 months; and 0.01 mm (95% CI, −0.01 to 0.03 mm) for 30 μg of sprifermin every 12 months. Compared with placebo, there were no statistically significant differences in mean absolute change from baseline in total WOMAC scores for 100 μg of sprifermin administered every 6 months or every 12 months, or for 30 μg of sprifermin every 6 months or every 12 months. The most frequently reported treatment-emergent adverse event was arthralgia (placebo: n = 46 [43.0%]; 100 μg of sprifermin administered every 6 months: n = 45 [41.3%]; 100 μg of sprifermin every 12 months: n = 50 [45.0%]; 30 μg of sprifermin every 6 months: n = 40 [36.0%]; and 30 μg of sprifermin every 12 months: n = 48 [44.0%]).CONCLUSIONS AND RELEVANCE Among participants with symptomatic radiographic knee osteoarthritis, the intra-articular administration of 100 μg of sprifermin every 6 or 12 months vs placebo resulted in an impro...