title: Melatonin uptake in prostate cancer cells: intracellular transport versus simple passive diffusion.
abstract: Melatonin, an indole mainly synthesized in the pineal gland during the dark phase, plays a role as an endogenous antioxidant and an anticancer agent in many tumors. Melatonin, at pharmacological concentrations, inhibits cell growth and induces neuroendocrine differentiation in prostate cancer cells. Classically it has been considered that melatonin enters freely into most of cells by passive diffusion through the cell membrane; however, there are few studies examining how melatonin is taken up by cancer cells. The aim of the present paper was to study the uptake of melatonin into human androgen-dependent LNCaP and androgen-independent PC-3 prostate cancer cells. Increased concentrations of melatonin induced a rapid and transitory rise in intracellular melatonin content in both cell types, with a peak of maximal content at 6 hr after melatonin addition, following a rhythmic uptake; melatonin was found in both cytoplasm and nuclear fractions. Inhibition of protein or RNA synthesis partially blocked melatonin uptake in both cell lines. Interestingly, melatonin pulse incubation led to a higher uptake after four cycles of pulse incubation. Neither extracellular Ca(2+)/K(+) alterations nor the presence of bovine serum albumin or charcoal-stripped serum modified the profile of melatonin uptake. On the contrary, chemical binding of melatonin to BSA totally prevented melatonin from entering into cells. The present data support the hypothesis that a facilitated diffusion or an active process rather than simple passive diffusion through the cell membrane is the major mechanism in melatonin uptake by prostate cancer cells and it accounts for its intracellular concentration (350 nM-3.3 microM), which is related to its anti-tumor actions.
authors.affiliation: Departamento de Morfología y Biología Celular, School of Medicine, University of Oviedo, Spain.
authors.forename: David
authors.initials: D
authors.lastname: Hevia
authors.forename: Rosa M
authors.initials: RM
authors.lastname: Sainz
authors.forename: Domingo
authors.initials: D
authors.lastname: Blanco
authors.forename: Isabel
authors.initials: I
authors.lastname: Quirós
authors.forename: Dun-Xian
authors.initials: DX
authors.lastname: Tan
authors.forename: Carmen
authors.initials: C
authors.lastname: Rodríguez
authors.forename: Juan C
authors.initials: JC
authors.lastname: Mayo
mesh_terms: D000704:Analysis of Variance; D001693:Biological Transport, Active; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism; D002458:Cell Fractionation; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism*; D002940:Circadian Rhythm; D003593:Cytoplasm / Q000378:metabolism*; D004058:Diffusion; D055459:Facilitated Diffusion; D005434:Flow Cytometry; D005786:Gene Expression Regulation / Q000502:physiology; D006801:Humans; D008051:Lipid Bilayers; D008297:Male; D008550:Melatonin / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000378:metabolism*; D012710:Serum Albumin, Bovine
chemical_list: D008051:Lipid Bilayers; D012710:Serum Albumin, Bovine; D008550:Melatonin; D011188:Potassium; D002118:Calcium