Signaling Systems Laboratory, Department of Chemistry and Biochemistry, University of California at San Diego, La Jolla, California 92093, USA.
TNF-induced NF-kappaB activity shows complex temporal regulation whose different phases lead to distinct gene expression programs. Combining experimental studies and mathematical modeling, we identify two temporal amplification steps-one determined by the obligate negative feedback regulator IkappaBalpha-that define the duration of the first phase of NF-kappaB activity. The second phase is defined by A20, whose inducible expression provides for a rheostat function by which other inflammatory stimuli can regulate TNF responses. Our results delineate the nonredundant functions implied by the knockout phenotypes of ikappabalpha and a20, and identify the latter as a signaling cross-talk mediator controlling inflammatory and developmental responses.