PARENT SESSION
Signal Transduction
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CYCLIC AMP IN OVARIAN CANCER CELLS BOTH INHIBITS PROLIFERATION AND INCREASES c-KIT EXPRESSION.
Shaw, Tanya1,2, Keszthelyi, Eniko1,2, Tonary, Angela 1,2, Cada, Michaela1,2, Vanderhyden, Barbara1,2, 1 2
ABSTRACT- The significant changes in the ovarian hormonal milieu in post-menopausal women may contribute to their increased risk for developing ovarian cancer. We hypothesize that the altered cell proliferation rates induced by hormone stimulation may be attributable to accompanying changes in the expression and/or activity of proto-oncogenes and growth factors, such as c-kit. C-kit encodes a tyrosine kinase receptor (Kit) that, when activated by its ligand (KL), stimulates proliferation, migration and survival. Greater than 70% of epithelial ovarian cancers co-express c-kit and KL. Since c-kit and KL expression can be differentially regulated by gonadotropic and steroid hormones in the normal ovary, the goal of these experiments was to examine the possible role of hormonally regulated c-kit and KL expression on ovarian cancer cell proliferation. Two ovarian cancer cell lines, HEY and OVCA 429, both of which express c-kit and KL, failed to show altered proliferation or gene expression in the presence of estradiol, progesterone, testosterone, follicle stimulating hormone or human chorionic gonadotropin, likely due to the loss of functional receptors from repeated cell culture. Treatment of HEY cells with dibutyryl cyclic AMP (dbcAMP), 8-bromo-cAMP, and cholera toxin over a range of concentrations caused a dose-dependent inhibition of HEY cell proliferation by up to 40, 62, and 38%, respectively. This inhibition of proliferation correlated with a dose-dependent increase in c-kit mRNA expression, yielding 5- to 7-fold elevations in transcript abundance; there were no changes in steady-state levels of KL transcripts. In order to determine whether Kit expression/activity was responsible for the observed decrease in proliferation, dbcAMP-treated HEY cells were exposed to either anti-Kit neutralizing antibodies, or the Kit inhibitor STI 571. Preliminary experiments show that these treatments do not alter the growth rate of control cells or reverse the dbcAMP-induced inhibition of proliferation. These results suggest that cAMP signalling pathways regulate both cell proliferation and c-kit expression in ovarian cancer cells, however, it appears that Kit is not assuming its traditional role as a growth factor.
KEY WORDS: c-kit , cyclic AMP, ovarian cancer, cell proliferation