title: Modulation of intracellular calcium and calmodulin by melatonin in MCF-7 human breast cancer cells.
abstract: The pineal hormone, melatonin, has been shown to inhibit the proliferation of the estrogen receptor alpha (ERalpha)-positive macrophage chemotactic factor (MCF)-7 human breast cancer cells. Previous studies from other systems indicate that melatonin modulates the calcium (Ca2+)/calmodulin (CaM) signaling pathway either by changing intracellular calcium concentration ([Ca2+]i) via activation of its G-protein coupled membrane receptors, or through a direct interaction with CaM. In this study, although melatonin alone had no effect on basal [Ca2+]i in MCF-7 cells, it significantly enhanced the elevation of [Ca2+]i induction by extracellular adenosine triphosphate (ATP), which increases [Ca2+]i via the G protein-coupled P2y-purinoceptor and the phospholipase C (PLC) pathway. Pretreatment of MCF-7 cells with 10(-7) M melatonin increased the 10(-5) M ATP-induced [Ca2+]i peak change from 79.4 +/- 11.6 nM to 146.2 +/- 22.3 nM. Furthermore, without changing total cellular CaM levels, melatonin markedly increased the amount of membrane-bound CaM to 237 and 162% of control levels after I and 6 hr of treatment, respectively. Cytosolic CaM levels were also elevated to 172% of control after 6 hr of melatonin treatment. Correlative growth studies demonstrated that ATP (10(-5) M) can stimulate MCF-7 cell growth, that melatonin can suppress MCF-7 cell proliferation, but that pretreatment of MCF-7 cells with melatonin followed by ATP(10(-5) M), like 10(-4) M ATP can further suppress MCF-7 cell proliferation; this indicates that melatonin's potentiation of ATP induced [Ca2+]i may be above the threshold for cell growth. Given the important role of [Ca2+]i and CaM in tumor cell homeostasis and proliferation and melatonin's modulation of [Ca2+]i, melatonin's effects on the Ca2+/CaM signaling pathway may play an important role in mediating the growth-inhibitory effect of melatonin on MCF-7 human breast cancer cells.
authors.affiliation: Department of Structural and Cellular Biology, Tulane University Cancer Center, Tulane University School of Medicine, New Orleans, LA 70112, USA.
authors.forename: Jun
authors.initials: J
authors.lastname: Dai
authors.forename: Edward W
authors.initials: EW
authors.lastname: Inscho
authors.forename: Lin
authors.initials: L
authors.lastname: Yuan
authors.forename: Steven M
authors.initials: SM
authors.lastname: Hill
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000187:drug effects / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D004357:Drug Synergism; D005260:Female; D006801:Humans; D008550:Melatonin / Q000494:pharmacology*; D015398:Signal Transduction; D013347:Subcellular Fractions; D014407:Tumor Cells, Cultured
chemical_list: D002147:Calmodulin; D000255:Adenosine Triphosphate; D008550:Melatonin; D002118:Calcium