Figure 2.
Effect of flavonoids and EGF on the kinase activity of A431 cellular proteins. (A) Cell lysates of 50 μg proteins were incubated with various flavonoids at 20 μM or with 100 nM EGF in the presence of [γ-32P]-ATP. Lanes: 1, control; 2, EGF; 3, luteolin; 4, quercetin; 5, genistein; 6, Taxifolin; 7, d-catechin; 8, naringenin; 9, kaempferol; 10, wogonin. Note that luteolin and quercetin both dramatically inhibited the phosphorylation of most protein bands, including the EGF receptor band (170-kDa), whereas genistein produced only a marginal (12%) decrease of the phosphorylation level of the 170-kDa band. (B) Cell lysates with equivalent amounts of protein (50 μg) were immunoprecipitated with anti-EGFR antibodies. After centrifugation, the supernatants were collected and then subjected to total kinase activity assay as described above. Lanes: 1, cell lysate; 2, EGF+cell lysate; 3. EGFR-removed cell lysate.