EXPRESSION OF INSULIN-LIKE GROWTH-FACTORS AND THEIR BINDING-PROTEINS IN THE ESTROGEN-RESPONSIVE ISHIKAWA HUMAN ENDOMETRIAL CANCER CELL-LINE

In uterine tissue, estrogen regulates various components of the insulin-like growth factor system; however, there are few suitable in vitro systems to examine these effects. Here we have examined the effects of 17-beta estradiol (E(2)) on expression and synthesis of insulinlike growth factors (IGF-I and IGF-II) and the insulin-like growth factor binding proteins (IGFBPs) by Ishikawa human endometrial cancer cells. Using a semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) assay, we demonstrated that both E(2) and 4-hydroxy-tamoxifen (OHT) enhanced IGF-I expression but had no effect on IGF-II expression. The pure antiestrogen ICI 182,780 had no effect on IGF-I expression and partially blocked the E(2) and OHT effect on IGF-I expression. The effect of epidermal growth factor (EGF), which is able to mimic some of the effects of E(2) in Ishikawa cells and uterine tissue, was also examined. EGF, unlike E(2), did not increase IGF-I expression but rather resulted in a significant decrease in IGF-I messenger RNA (mRNA) levels. EGF also resulted in a small, nonsignificant increase in IGF-II mRNA levels. IGFBP-3, -5, and -6 mRNAs were detected by Northern blot analyses of Ishikawa cells RNA. However, only IGFBP-3 was consistently detected by ligand blotting of conditioned medium. E(2) had no significant effect on expression of any of the binding proteins, whereas EGF increased IGFBP-5 mRNA levels. These data provide the first in vitro demonstration of regulation of IGF-I expression by E(2). The Ishikawa cell line may provide a useful model to further investigate the molecular mechanisms underlying E(2) regulation of IGF-I expression. Furthermore, we have demonstrated a clear dissociation of the effects of E(2) and EGF on IGF-I expression in this cell line.