and Insulin-like Growth Factor 1 Receptor Abrogates All Requirements for Exogenous Growth Factors1

BALB/c3T3 cells are exquisitely growth regulated and require both platelet-derived growth factor and insulin-like growth factor-i (IGF-i) for optimal proliferation. BALB/c3T3 cells that constitutively express IGF-i and elevated levels of IGF-i receptor (IGF-iR) are capable of growth in serum-free medium without the addition of any exogenous growth factors. BALB/c3T3 cells overexpressing only the IGF-1R plasmid required IGF-i or insulin for serum-free growth. Antisense oligodeoxynucleotides complementary to IGF-i R mRNA inhibited IGF-i-mediated cell growth. Under these conditions, neither the epidermal growth factor receptor nor phospholipase C’yi was autophosphorylated. These findings indicate that constitutive expression of IGF-i and IGF-1R allows 3T3 cells to grow in serum-free medium without addition of those exogenous growth factors that are required by the parent cell line