Fig. 5. Growth inhibition depends on tyrosine 367 and glutamine 370 of the IL-9R. BW5147 cells were transfected with the following receptors: hIL-9R (wild-type); mut1 (Tyr-367 to Phe, abrogates STAT activation); mut6 (Leu-368 to Arg, results in the preferential activation of STAT1 and STAT3); and mut7 (Gln-370 to Leu, preferential activation of STAT5) (10) . Clones expressing a similar level of receptor were stimulated with hIL-9. After 3 days, proliferation was evaluated by measuring [3H]thymidine incorporation. A representative experiment is shown, with SDs (bars) calculated from triplicate cultures.