INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEIN SECRETION BY BREAST-CARCINOMA CELL-LINES - CORRELATION WITH ESTROGEN-RECEPTOR STATUS

Breast tumor cell lines have been shown to secrete several distinct polypeptide growth factors, although conflicting results exist for the insulin-like growth factors (IGFs). In contrast a limited number of breast tumor cell lines have definitely been shown to secrete the high affinity IGF binding proteins (IGFBPs) that modify IGF actions. To characterize the types of IGFBPs that are secreted by breast tumor cell lines, conditioned medium was collected from seven separate tumor cell lines, three of which were estrogen receptor (ER) negative, and four of which were ER positive. All three of the ER negative cell lines, MDA-231, MDA-330, and HS578T, secreted binding proteins of 49, 000 and 43, 000 Mr(IGFBP-3) as well as 29, 000 (IGFBP-1) and 24, 000 Mr. In contrast, all four ER positive cell lines secreted 34, 000 (IGFBP-2) or 24, 000 Mrforms, and none secreted the 49, 000 and 43, 000 or 29, 000 Mrforms. BT-20, a cell line that is positive for ER messenger RNA (mRNA) but negative for ER protein, secreted predominantly a 34, 000 Mrprotein. The amount of total IGFBP activity released in 24 h ranged between 0.4 and 5.6 nM equivalents of IGFBP-1, and there was no significant difference between the ER positive and negative cell lines. The MCF-7 cells that produced predominantly 34, 000 and 24, 000 Mrforms showed a 1.8-fold increase in IGFBP secretion after estrogen stimulation. Immunoblotting and a specific RIA for IGFBP-1 showed that only the ER negative lines MDA-330, MDA-231, and HS578T secreted this form. Northern blotting analysis for the mRNA encoding this protein showed that both MDA-330 and MDA-231 contained a single 1.6 kilobase mRNA species that hybridized with an IGFBP-1 complementary DNA (cDNA) probe. Immunoblotting analysis of the other cell lines showed that only the 34, 000 Mrform secreted by the ER positive cell lines reacted with IGFBP- 2 antisera. Exposure of the conditioned media from the three ER negative cell lines to N-glycanase revealed that the 49, 000 and 43, 000 Mrforms of IGFBP were glycosylated and therefore probably represent IGFBP-3. We conclude that ER negative cell lines secrete three forms of IGFBPs, IGFBP-1, IGFBP-3, and a 24, 000 Mrform. In contrast, the ER positive cell lines secrete predominantly IGFBP-2 and the 24, 000 Mrform but do not secrete IGFBP-3 or 1. Secretion of these forms is stimulated by estrogen. These findings indicate that breast tumor cell lines secrete specific forms of IGFBPs and that ER negative and positive tumor cell lines differ in the forms of IGFBPs that are produced. These findings may have implications for understanding the role of the IGFs in controlling breast carcinoma cell proliferation. © 1990 by The Endocrine Society.