Table 1.

EGF Stimulation, but Not Thrombin Stimulation, of p70^S6k Activity Is Abolished by AG1478

Stimulus	p70S6k activity (percentage of unstimulated control)
Unstimulated control	100 ± 2.7
Unstimulated + AG1478	68 ± 4.2
EGF	678 ± 87
EGF + AG1478	81 ± 3.7
Thrombin	231 ± 21
Thrombin + AG1478	171 ± 15

Swiss 3T3 cells were left unstimulated or were activated with EGF (10 nM) or thrombin (1 U/ml) in the presence or absence of the EGF receptor kinase inhibitor AG1478 (0.5 μM) for 1 h. Cells were then lysed with Triton X-100–containing buffer and p70^S6k was immunoprecipitated from the membrane plus cytosol fraction. The activity of p70^S6k precipitated was quantitated by a kinase assay involving phosphorylation of an S6 kinase peptide substrate in the presence of [γ-³²P]ATP. There was no difference in amount of p70^S6k protein precipitated in the different samples (not shown). It can be seen that AG1478 totally inhibited EGF stimulation of p70^S6k while only partially inhibiting the unstimulated value and that stimulated by thrombin. Results are the mean ± SE of six samples from two experiments.