Efficient inhibition of macrophage TNF-α production upon targeted delivery of K48R ubiquitin

K48R ubiquitin (K48R-Ub) is an analogue of native ubiquitin that does not form polyubiquitin chain conjugates. Targeted delivery of this recombinant mutant ubiquitin to human macrophages results in an intracellular increase in the ubiquitin analogue. IkB alpha polyubiquitination and degradation were significantly inhibited in K48R-Ub targeted macrophages upon stimulation with lipopolysaccharide. The ability to reduce IkB alpha degradation was also associated with a reduced production of TNF-alpha, the gene of which is under NF-kB control. At a concentration of 0.1 mu M, dexamethasone was less effective than K48R-Ub in preventing IkB alpha depletion and TNF-alpha release. These data suggest that ubiquitin analogues are potent suppressors of TNF-alpha release in macrophages.