Abstract
In our earlier study we have demonstrated that MCF-7 cell line expresses all three opioid receptor types, micro, delta and kappa (MOR, DOR and KOR, respectively), but predominantly MOR. Morphine, as well as endogenous MOR-selective agonists, endomorphin-1 and endomorphin-2 were shown to decrease MOR gene expression in MCF-7 cells. Opioid antagonist - naloxone -produced the opposite effect, increasing MOR gene expression. In this study we investigated and compared the influence of several opioid antagonists of alkaloid structure (beta-funaltrexamine and naloxonazine) and of peptide structure: [Dmt(1), D-1-Nal(4)]endomorphin-2, [Dmt, D-2-Nal(4)]endomorphin-1, and [Dmt, D-2-Nal(4)]endomorphin-2 on MOR up-/down-regulation and proliferation in MCF-7 cell line. MCF-7 cells were incubated with opioids. The levels of MOR mRNA were assessed using quantitative real-time RT-PCR assay. Cell growth was measured by Mosmann tetrazolium salt assay. It was shown that all tested opioid antagonists produced up-regulation of MOR gene expression, but the strongest effect was observed with naloxonazine. However, none of the antagonists at concentrations as high as 10(-4) M showed any antiproliferative effects on MCF-7 cells, neither in the presence or absence of beta-estradiol. It seems that up- or down-regulation of MOR mRNA levels has no direct effect on cell proliferation.
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