Expression of adrenomedullin in long-term oestrogen-deprived human breast cancer cells
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KeywordsBreast Cancer Breast Cancer Cell Tamoxifen MCF7 Cell Human Breast Cancer
Oestrogen is a major requirement for the growth of human breast cancer cells. Current treatments are aimed at reducing the action of oestrogen with antioestrogen therapy. However, many patients are able to progress to a state where they no longer respond to antioestrogen therapy. Long-term growth of breast cancer cell lines in the absence of oestrogen leads to the development of acquired resistance where the cells are able to grow without the addition of oestrogen, they can still be inhibited by antioestrogens and there is no loss of oestrogen receptor alpha. The aim of this work was to identify novel molecular markers that could indicate impending failure to endocrine therapy. Adrenomedullin is a 52-amino-acid peptide which may play a role in tumour survival and angiogenesis. Microarray data comparing oestrogen-maintained MCF7 cells with long-term oestrogen-deprived MCF7 cells showed that the expression of adrenomedullin mRNA was 12-fold upregulated after more than 1 year of culture in the absence of oestrogen. Real-time RT-PCR data were able to confirm the increase in the levels of adrenomedullin mRNA in long-term oestrogen-deprived cells. Immunocytochemistry using a monoclonal antibody specific for adrenomedullin was also able to show an increase in the amount of adrenomedullin protein in long-term oestrogen-deprived cells. Furthermore, long-term treatment of oestrogen-maintained cells with tamoxifen and fulvestrant led to an increase in the level of adrenomedullin mRNA which was not observed in long-term oestrogen deprived cells. Further validation with tumour samples is required to examine the importance of adrenomedullin as a possible marker of endocrine resistance in human breast cancer.