Figure 1
Upregulation of an autocrine growth factor loop during a model of breast cancer progression.
(A) T4-2 (malignant) cells, which grow independently of exogenous EGF, had significantly higher activity of EGFR than their phenotypically normal counterpart, S1 (nonmalignant) cells. The level of EGFR phosphorylation is consistent with activation by a soluble factor produced in these cells. Ponceau S staining was used as a loading control. (B) S1 cells were starved of EGF for 12 hours and then stimulated for 10 minutes with either T4-2 conditioned medium (CM) or 5 ng/ml EGF. A 5 minute pretreatment with Iressa (0.3 nM) abolished MAPK activation induced by the conditioned medium and by EGF. (C) RT-PCR analysis shows that AREG and TGFA were transcriptionally upregulated in T4-2 relative to S1 cells. GAPDH was used as a loading control. (D) ELISA of conditioned medium shows that T4-2 cells secreted significantly more AREG and TGF-α than did S1 cells. (E) S1 cell proliferation in the presence of all EGFR ligands (860 pM) was significantly different from control (Ctrl).
