Steady-state mRNA expression for growth factors in DMBA-induced rat mammary tumors.

Steady-state mRNA levels were examined for insulin-like growth factors (IGF) I and II, transforming growth factor alpha (TGF alpha) and its receptor and the epidermal growth factor (EGF) receptor in mammary tumors induced by DMBA in rats. An abundant 4.8 kb TGF alpha transcript was identified in all tumors, along with a 7.5-8.0 kb IGF-I transcript. A presumptive 2.9 kb IGF-II transcript was also identified in all tumors. Northern analyses and receptor autophosphorylation studies failed to detect EGF receptors in any mammary tumors. These findings suggest the potential for autocrine or paracrine influences of IGF-I and IGF-II in this tumor model and a possible paracrine influence of TGF alpha in tumor-induced neovascularization.