Figure 2

PDGF receptors are inversely regulated with IGF-IR. Western blotting was used to examine expression in response to varying IGF-IR levels. Doxycycline was withdrawn from MTB-IGFIR mice with mammary tumors and tissue was collected 24 or 48 h later. Levels of PDGFRs were assessed and compared to that of tumors with IGF-IR induction (a). IGF-IR and PDGFR expression in a cell line (RJ345) created from a IGF-IR-dependent primary mammary tumor and two cell lines (RJ348 and RJ348) created from different IGF-IR-independent recurrent spindle tumors (b). Four cell clones expressing low levels of IGF-IR were generated through serial passage in the absence of doxycycline. Confirmation of IGF-IR downregulation as well as determination of PDGFRα and PDGFRβ levels was performed (c). PDGFR levels in RM11A cells grown in vivo with (RM11A + dox) or without (RM11A-dox) doxycycline induction. Tissue was collected when tumors reached 17 mm in diameter (d). For all Western blots, β-actin served as a loading control.