The main purpose of this study was to examine the effect of 17β-estradiol (E2) on the production of insulin-like growth factor-I (IGF-I) and insulin-like growth factor binding proteins (IGFBP) by GH4C1 cells, a pituitary tumor cell line that displays many phenotypic properties of the anterior pituitary lactotroph. At a low population density (10 500 cells/cm2), E2 stimulated production of IGF-I by 4.2-fold. At this density, the antiestrogen tamoxifen (TAM) had no significant effect, whereas triiodothyronine (T3), which has been demonstrated to increase the level of IGF-I mRNA in the parental GH3 cell line, stimulated IGF-I production by 3.3-fold. Both E2 and T3 also stimulated GH4C1 cell proliferation at this population density. At a four-fold higher population density (42 000 cells/cm2), E2, TAM and T3 had little effect on IGF-I production. E2 failed to stimulate proliferation of GH4C1 cells at high density, and T3 stimulated production of IGFBP-3 by 6- and 11-fold, respectively. At high density, the abilities of E2 and T3 to stimulate IGFBP-3 production were somewhat reduced. TAM had no effect on IGFBP-3 production at either population density. These data indicate that E2 and T3 stimulate production by GH4C1 cells of IGF-I through a mechanism that is sensitive to changes in population density.
- Insulin-like growth factor binding protein
- Insulin-like growth factor-I
ASJC Scopus subject areas
- Molecular Biology