The pineal hormone, melatonin has repeatedly been shown to inhibit the proliferation of estrogen receptor alpha (ERalpha)-positive MCF-7 human breast cancer cells. Previous reports have suggested that the actions of melatonin can be mediated either through G protein-coupled membrane receptors, or via retinoid orphan receptors (RORalpha), which constitutively activate gene transcription through their corresponding response elements termed ROREs. Transient transfection assays using an RORE-luciferase reporter construct have shown that the endogenous (RORalpha), receptors expressed in MCF-7 breast cancer cells exhibited a high basal level of transcriptional activity, which was further stimulated by serum. In the presence of serum, both the transcriptional activity and DNA binding ability of (RORalpha), were repressed by melatonin treatment, even though melatonin had no effect on RORalpha protein levels. Although RORalphas were originally proposed as nuclear receptors for melatonin, the direct binding of melatonin to these receptors can not be repeated. Therefore, it is not clear how melatonin can modulate (RORalpha), functions in MCF-7 cells. Consistent with the results from other systems, RORalpha transcriptional activity in MCF-7 cells was found to be responsive to intracellular calcium concentration ([Ca2+]i), calmodulin (CaM), and Ca2+/CaM-dependent protein kinases. Meanwhile, melatonin not only affected CaM subcellular distribution, but also modulated [Ca2+]i change induced by another known calcium stimulator, ATP, indicating that melatonin may regulate RORalpha transcriptional activity via its modulation of the Ca2+/CaM signaling pathway in MCF-7 cells. In exploring the biological functions of (RORalpha), receptors, we found that the decrease in RORalpha protein levels by an (RORalpha), antisense oligonucleotide con-elated with growth inhibition in MCF-7 cells. Our data suggest that RORalpha receptors may play a role in stimulating the proliferation of MCF-7 cells, and thus, the repressive effect of melatonin on these receptors may, at least in part, mediates melatonin's antiproliferative effects on breast cancer cells / acase@tulane.edu
| Identifer | oai:union.ndltd.org:TULANE/oai:http://digitallibrary.tulane.edu/:tulane_23618 |
| Date | January 2000 |
| Contributors | Dai, Jun (Author), Hill, Steven M (Thesis advisor) |
| Publisher | Tulane University |
| Source Sets | Tulane University |
| Language | English |
| Detected Language | English |
| Rights | Access requires a license to the Dissertations and Theses (ProQuest) database., Copyright is in accordance with U.S. Copyright law |
Page generated in 0.0159 seconds