Differential induction of TTP mRNA accumulation mediated by TNFR1 and TNFR2

. BMMφs were prepared as described in “Materials and methods” and were stimulated with increasing concentrations of rmTNF-α for 30 minutes. Northern blots from these experiments are shown on the left; the TTP and cyclophilin (Cyclo) mRNAs are indicated. On the right is the PhosphorImager quantitation of these blots after the TTP mRNA levels had been normalized for cyclophilin mRNA levels. WT macrophages exhibited detectable expression of TTP mRNA after stimulation with as little as 0.1 ng/mL rmTNF-α. However, in the absence of both TNFRs (TNFR1/2KO), there was no induction of TTP mRNA expression, even at the highest concentration of rmTNF-α used, 10 ng/mL. In the absence of TNFR1 (TNFR1KO), there was also no induction of TTP mRNA expression. However, in the absence of TNFR2 (TNFR2KO), rmTNF-α induced the expression of TTP mRNA, but there was a shift to the right of one order of magnitude in the concentration-dependence curve compared with that seen in WT macrophages. The experiment shown here is representative of 3 independent experiments using cells derived from different groups of animals.