Type I insulin-like growth factor receptor gene expression in normal human breast tissue treated with oestrogen and progesterone

The epithelial proliferation of normal human breast tissue xenografts implanted into athymic nude mice is significantly increased from basal levels by oestradiol (E(2)), but not progesterone (Pg) treatment at serum concentrations similar to those observed in the luteal phase of the human menstrual cycle. Type I IGF receptor (IGFR-I) mRNA and protein have been shown to be up-regulated by E(2) in MCF-7 breast cancer cells in vitro in which IGF-I and E(2) act synergistically to stimulate proliferation. We have investigated the expression of the IGFR-I mRNA in normal human breast xenografts treated with or without E(2) or PS alone and in combination. Northern analysis of 20 mu g of RNA extracted from the breast xenograft samples showed no hybridization with P-32-labelled IGFR-I probe, although an 11-kb species of IGFR-I mRNA could be seen when 20 mu g of RNA extracted from either MCF-7 breast cancer cells or human breast carcinomas was examined in this way. In order to analyse the expression of IGFR-I mRNA in breast xenografts, a quantitative reverse transcription - polymerase chain reaction (RT-PCR) was employed in which RNA loading, reverse transcription and PCR efficiencies were internally controlled. The data indicate that the IGFR-I mRNA is up-regulated by two to threefold compared with untreated levels by 7 and 14 days E(2) treatment. In contrast, 7 or 14 days Pg treatment downregulates the receptor mRNA to approximately half that of untreated levels, whereas combination E(2) and Pg treatment produced a twofold increase in IGFR-I mRNA revels compared with untreated tissue. The results are consistent with the suggestion that E(2) may act to stimulate proliferation indirectly via a paracrine mechanism involving IGFs in normal as well as malignant human breast epithelial cells.