Involvement of Transforming Growth Factor α/Epidermal Growth Factor Receptor Autocrine Growth Mechanism in an Ovarian Cancer Cell Line in Vitro

Although transforming growth factor (TGF) α and epidermal growth factor (EGF) receptor (EGFR) autocrine mechanism is widely demonstrated in many kinds of cancers, its biological significances still remain circumstantial. We critically assessed the significance of this mechanism on the growth of an ovarian cancer cell line. Northern blot analysis in polyadenylated RNA isolated from cells by using ³²P-labeled pre-TGFα, EGFR, and prepro-EGF complementary DNAs as probes revealed that pre-TGFα and EGFR but not prepro-EGF gene transcripts were expressed in the cell. TGFα and EGFR but not EGF proteins were observed by immunocytochemical stainings, using monoclonal antibodies against human TGFα, EGFR, and EGF, respectively. This cell line possessed a class of high affinity EGF receptor by ¹²⁵I-EGF binding studies; K₄ being 2.9 × 10⁻¹⁰ m and B_max to be 7.7 × 10⁴ sites/cell. As much as 1.12 ± 0.14 ng (SD; n = 3)/10⁷ cells/24 h of TGFα was secreted in the conditioned media. These results suggested the expression of a TGFα/EGFR autocrine mechanism in this cell line. We, therefore, assessed the biological significance of this mechanism on the growth of this cell line in serum-free monolayer cell cultures. Although 0.1, 1.0, and 10 nm concentrations of TGFα did not show significant growth promotion, monoclonal antibodies against TGFα and EGFR but not EGF significantly inhibited cell growth. All these data suggested the biological importance of a TGFα/EGFR autocrine mechanism on the growth of this cell line in vitro.