Kit-induced activation of Jak3 is dependent on IL-7R.(A) Kit-mediated activation of Jak3 is significantly stronger in the presence of IL-7R. 293T cells transiently coexpressing Kit and Jak3 in the presence (lanes 1,2) or absence (lanes 3,4) of IL-7R were stimulated with KL for 5 minutes, and tyrosine phosphorylation (top panel) and protein amounts of immunoprecipitated Jak3 (bottom panel) were compared between unstimulated (lanes 1,3) and stimulated (lanes 2,4) cells. (B) Kit-induced total tyrosine phosphorylation and activation of Erk1/2 is independent of IL-7R. Lysates were separated on SDS-PAGE and total tyrosine phosphorylation (first panel) as well as the amount of phosphorylated ERK1/2 were analyzed (fifth panel). Lysates were probed with antibodies as indicated to demonstrate Kit, γc, IL-7Rα (second to fourth panels), and endogenous ERK2 expression (bottom panel). (C) Quantification of 4 independent experiments analyzing KL-induced phosphorylation of Jak3 (right) and ERK1/2 (left graph) either in the presence (+) or absence (−) of γc and IL-7Rα. Results are expressed as fold increase of relative phosphorylation (see “Materials and methods” for details). Single experiments are shown in gray symbols (■, ♦, ▴, ●), the average is shown in black (X) and contains the error bars (standard error). P values were determined by paired t test analysis.