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ABSTRACT

Human MCF-7 breast cancer cells have been studied to determine their suitability as an autocrine model for the synthesis, secretion and action of insulin-like growth factor-I (IGF-I). Secretion of immunoreactive (ir-) IGF-I into serum-free medium was very low (<500 pg/10⁶ cells per day). Northern blot hybridization detected at least two IGF-I messenger RNA transcripts (∼4·6 and ∼1·8 kb) which were similar in size to those reported in other human and rat tissues. IGF-II mRNA was also detected but at low abundance. Cell proliferation was stimulated in a dose-responsive manner by exogenous IGF-I (10–30 ng/ml). Addition of a monoclonal antibody against IGF-I to MCF-7 cells in serum-free medium caused an inhibition of cell proliferation, suggesting that endogenous locally produced IGF-I does play an autocrine/paracrine role in MCF-7 cell growth. Proliferation of MCF-7 cells was sensitive to oestradiol (10 nm) in the absence but not in the presence of the weakly oestrogenic pH indicator phenol red. Neither IGF-I secretion nor IGF-I mRNA synthesis, however, was affected by addition of oestradiol. Similarly, GH, dexamethasone or dexamethasone plus oestradiol had no effect on either parameter.

These data indicate that MCF-7 cells synthesize, secrete and respond to IGF-I. The very low levels of ir-IGF-I produced and their apparent lack of hormonal modulation suggest, however, that further studies are required to establish whether IGF-I plays a major physiological role in growth and development of MCF-7 cells.

ABSTRACT

The aim of this study was to establish the gestational- and labour-associated variation in the relative abundance of prostaglandin synthase-1 (PGHS-1) and prostaglandin synthase-2 (PGHS-2) mRNA in ovine placenta (cotyledons). Cotyledons were collected from non-labouring ewes at 40–145 days of gestation (n=25) and from ewes in active labour (145–147 days, n=5). The relative abundance of PGHS-1 and PGHS-2 mRNA transcripts was determined by Northern blot analysis and laser densitometry, using a 2·3 kb sheep and a 1·2kb mouse cDNA probe respectively. Data were expressed as a ratio of PGHS transcript hybridization/18S rRNA hybridization. During pregnancy, the relative abundance of PGHS-2 mRNA increased sevenfold, from 0·19±0·04 at 40–85 days (n=5) to 1·39±0·05 at 140–145 days (n=4) (P<0·01). PGHS-1 mRNA relative abundance did not change significantly (P>0·05) during gestation. Neither PGHS-1 nor PGHS-2 mRNA relative abundance changed significantly in association with labour onset at term (n=5) when compared with the relative abundance observed at 140–145 days (n=4) (P>0·05). The data obtained in this study are consistent with the hypothesis that PGHS-1 is constitutively expressed in ovine placenta during pregnancy and at the time of labour, and that PGHS-2 is induced during the second half of pregnancy. It remains to be established to what extent these two isozymes contribute to the net prostaglandin-forming capacity of the ovine placenta, particularly at the time of labour.