Constitutive activation of Stat 3 oncogene product in human ovarian carcinoma cells

Objective. Stat 3 functions in transducing signals from the cell's surface to its nucleus and activation of gene transcription. Aberrations of Stat 3 in breast cancer have raised the possibility of its contribution to oncogen esis. Our goal was to examine ovarian cancer cell lines to determine whethe r Stat 3 plays a relevant role in ovarian carcinogenesis. Methods. Protein lysates were extracted from normal ovarian surface epithel ial cells and malignant cells. Western blotting techniques were performed w ith phosphorylation-independent or phosphorylation-specific Stat 3 (tyrosin e 705) antibody. Confirmation of Stat 3 activation was determined by a luci ferase reporter driven by a promoter containing Stat 3-specific binding sit es. Bcl-x(L) and cyclin D-1 were also analyzed by Western blotting. Results. MDAH 2774, OV-1063, Caov-3, and O.C. 22819 expressed high levels o f phosphorylated Stat 3. In contrast, A2780 and normal ovarian surface epit helial cells had little Stat 3 phosphorylation recognized. Confirmation of persistent activation of Stat 3 activity was shown by transfection of cells with a Stat 3 luciferase reporter. Potential downstream mediators of Stat 3 including Bcl-x(L) and cyclin D-1 were also evaluated. In cells expressin g activated Stat 3, high levels of both Bcl-x(L) and cyclin D-1 were detect ed, whereas in A2780 cells, which did not express activated Stat 3, only lo w levels of Bcl-x(L) and cyclin D-1 were expressed. Conclusions. Constitutive activation of Stat 3 is present in ovarian cancer lines but not in normal ovarian surface epithelial cells. Activation of St at 3 is a common event during oncogenic transformation upstream to both Bcl -x(L) and cyclin D-1. The relationship of this aberrancy of ovarian carcino ma harboring activated Stat 3 deserves further investigation. (C) 2000 Acad emic Press.