Insulin/IGF-1 modulation of the expression of two estrogen-induced genes in MCF-7 cells

Estrogen responses of human breast cancer cell lines have frequently been shown to be promoted by insulin. We have examined the action of insulin, and its interaction with estradiol, in regulating the expression of the estrogen-induced genes, LIV-1 and pS2. Both hormones cause increases in mRNA levels of the two genes but do so by distinct mechanisms. The concentration of insulin required to produce this effect suggests that it is acting via its ability to bind to the IGF-1 receptor. Both insulin and estradiol exert their effects at the level of transcription. Induction by insulin is dependent upon continued protein synthesis whereas induction by estradiol is not. Induction by both insulin and estradiol is prevented by the pure antiestrogen, ICI 164384, indicating the requirement for an activatable estrogen receptor. Insulin does not stimulate LIV-1 expression via the androgen receptor. These results demonstrate that both estradiol and insulin can stimulate the transcription of these estrogen-inducible genes, by separate mechanisms both of which involve the estrogen receptor.