Background: The GH/IGF-I axis has been implicated in the development of breast cancer. However the regulation of local expression of the GH/IGF-I axis in breast tissue is unknown. In vitro studies have suggested an inhibitory effect of ghrelin on the proliferation of breast cancer cell lines, although the mechanisms for this action are unknown.
Aims: Using a physiologically relevant culture system for breast tissue explants, to investigate the effects of ghrelin on (1) GH and IGF-I mRNA levels in normal and malignant breast tissue, and (2) the release of GH into the media from the explants.
Methods: 10 paired samples of normal (N) and malignant (T) breast tissue were obtained at surgery and individually cultured in serum-free media (DMEM) with or without exogenous ghrelin (10-9M) for 4, 24 and 48 hours. Total RNA was extracted and mRNA levels of IGF-I, GH and GAPDH quantitated by real-time RT-PCR ('Taqman') and expressed as copy number/microgram total RNA. The GH concentration in the media from 3 paired samples was assessed using an ELISA (NETRIA; sensitivity 0.4 milliunits/litre).
Results: (1) GAPDH and GH were universally expressed in all samples (median 2.5E+09 and 6.2E+06 copies respectively), but there was no change in response to ghrelin. There was a significant down regulation of IGF-I mRNA in explants incubated with ghrelin compared to media only at 24 hours in both normal (median 1.00E+00 vs 2.01E+03, p<0.05) and malignant tissue (median 5.0E+00 vs 1.08E+03, p<0.03). (2) There was no detectable GH in the media from any of the samples.
Conclusion: The specific down-regulation of IGF-I mRNA in response to ghrelin, with no effect on GAPDH or GH mRNA levels may explain the previously reported inhibitory effects by ghrelin on proliferation of breast cancer cells. The mechanisms for this down regulation remain to be determined.
22 - 24 Mar 2004
British Endocrine Societies