CHANGES IN INSULIN-LIKE GROWTH-FACTOR-I RECEPTOR EXPRESSION AND BINDING-PROTEIN SECRETION ASSOCIATED WITH TAMOXIFEN RESISTANCE AND ESTROGENINDEPENDENCE IN HUMAN BREAST-CANCER CELLS IN-VITRO
D. Mccotter et al., CHANGES IN INSULIN-LIKE GROWTH-FACTOR-I RECEPTOR EXPRESSION AND BINDING-PROTEIN SECRETION ASSOCIATED WITH TAMOXIFEN RESISTANCE AND ESTROGENINDEPENDENCE IN HUMAN BREAST-CANCER CELLS IN-VITRO, Cancer letters, 99(2), 1996, pp. 239-245
Conditioned medium from a series of human breast cancer cell lines rep
resenting the phenotypes of estrogen dependence (ZR-75-1, MCF-7), tamo
xifen resistance (21R-75-9a1, LY2) and estrogen independence (ZR-PR-LT
) contained four detectable insulin-like growth factor binding protein
s (IGFBPs) of MW 24, 34, 44 and 70 kDa. In the tamoxifen resistant lin
es secretion of the 24 kDa IGFBP was depressed in comparison to the pa
rent lines whilst secretion of the 44 kDa IGFBP was unaffected. Secret
ion of this species by ZR-PR-LT cells was reduced. Following incubatio
n in medium containing 1% serum both tamoxifen resistant cell lines se
creted higher levels of the 44 kDa IGFBP than the respective parent li
nes. These changes in IGFBP secretion associated with the development
of tamoxifen resistance and estrogen independence were accompanied by
changes in the expression of receptors for IGF-I.