ABSENCE OF CONSTITUTIVE EGF RECEPTOR ACTIVATION IN OVARIAN-CANCER CELL-LINES

Previous investigators have noted that certain ovarian cancer cell lin es secrete and respond to transforming growth factor-alpha (TGF-alpha) , suggesting that endogenous activation of the epidermal growth factor (EGF) receptor through autocrine or paracrine mechanisms might contri bute to the proliferative response. In order to determine whether auto crine stimulation was partly responsible for the proliferative respons e in ovarian cancer, we investigated whether the EGF receptor expresse d by ovarian cancer cell lines was constitutively activated as assesse d by the presence of tyrosine phosphorylation. A specific anti-phospho tyrosine antibody was used in conjunction with an immunoblotting techn ique in order to detect EGF receptor phosphorylation in ovarian cancer cell lines in the absence and presence of exogenous EGF. The effects of neutralising anti-EGF receptor antibody on the proliferation of ova rian cancer cell lines was also examined. We found no evidence for con stitutive tyrosine phosphorylation of the p170 EGF receptor in eight e pithelial ovarian cancer cell lines tested, although each line demonst rated inducible phosphorylation in response to exogenous EGF. The abse nce of constitutive EGF receptor activation was also noted when cells were grown under high density conditions, thus excluding a role for me mbrane-bound EGF or TGF-alpha in this process. Media conditioned by fi ve ovarian cancer cell lines, as well as malignant ascites obtained fr om 12 different ovarian cancer patients, were not capable of stimulati ng EGF receptor phosphorylation. Finally, the proliferation of ovarian cancer cell lines was not significantly inhibited in the presence of neutralising anti-EGF receptor antibody. These data suggest that EGF r eceptor activation through autocrine pathways is not a major mechanism for the growth of many ovarian cancer cell lines. Other pathways of s ignal transduction which bypass the requirement for EGF receptor activ ation may be important in the proliferation for ovarian cancer cells. Such EGF receptor-independent pathways may limit the effectiveness of strategies designed to inhibit ovarian cancer cell growth through disr uption of EGF receptor function.