FIG 4.

TRAF6 catalyzes STAT3 ubiquitination upon S. Typhimurium infection. (A) Traf6^+/+ MEFs were first serum starved and then infected with S. Typhimurium at an MOI of 10 for the indicated times. WCEs were collected for immunoprecipitation (IP) with rabbit anti-STAT3, followed by Western blotting (IB) with mouse anti-STAT3 and mouse anti-ubiquitin. WCEs were probed with rabbit anti-STAT3 and rabbit anti-tubulin (as a loading control). (B) Importance of the TRAF6 C70 residue for S. Typhimurium-induced STAT3 ubiquitination and phosphorylation. Traf6^−/− MEFs were transfected with either mock plasmids (Vector), pcDNA4-FLAG-TRAF6 (WT), or pcDNA4-FLAG-TRAF6 C70A (C70A) for 24 h before infection with S. Typhimurium for 8 h. STAT3 was immunoprecipitated as described for panel A, and the phosphorylation of STAT3 was detected as for Fig. 3B.