Fig. 5. EGF signaling targets SID repression activity. (A) Deletions of TIEG2 NTD expressing D1, D2 and D3 were cloned as GAL4 DBD fusion constructs and co-transfected into CHO cells in the absence or presence of caMEK1, along with the GAL4 luciferase reporter plasmid. Note that co-expression of caMEK1 strongly antagonizes the repression activity of NTD (lane 2) and D3 (lane 5), but not D2 (lane 4). Also note that D1 repression activity is slightly antagonized by caMEK1 co-transfection (lane 5). (B) Mutations M1–M5 were generated in the context of the GAL4 D3 construct, and GAL4-based reporter assays were performed. Note that caMEK1 co-expression inhibits the repression activity of wild-type D3 (lane 2) and that mutations M1–M4 partially block caMEK1 inhibition of SID repression activity (lanes 3–6). CaMEK1-mediated inhibition is almost abolished in D3 M5 (lane 7).