title: Evidence for a biphasic apoptotic pathway induced by melatonin in MCF-7 breast cancer cells.
abstract: Previous investigations demonstrated that melatonin exerts an oncostatic action on estrogen-responsive breast cancer, both in vitro and in vivo. Nevertheless, the pro-apoptotic effect of melatonin is still a matter of debate. An experimental study was undertaken to focus on melatonin-related apoptosis and to identify the apoptotic pathways involved. Whole cell-count, flow-cytometry analysis and proteins involved in apoptotic pathways [p53, p73, murine double minute 2 (MDM2), caspases-9,-7,-6, cleaved-poly ADP ribose polymerase (PARP), Bcl-2, Bax and apoptotic inducing factor (AIF)] were investigated in human MCF-7 breast cancer cells treated with physiological (1 nM) concentration of melatonin. Melatonin exerts a significant growth-inhibitory effect on MCF-7 cells, becoming evident after 72 hr and thereafter increasing linearly up to 144 hr. In this model, the growth-inhibition is transforming growth factor beta 1 (TGFbeta1)-dependent and it might be reversed by adding an anti-TGFbeta1 antibody. Melatonin induces a significant rise in apoptotic rate, at both 24 and 96 hr. The anti-TGFbeta1 antibody almost completely suppresses melatonin-related late apoptosis; however, early apoptosis is unaffected. Early programmed cell death is associated with a significant increase in the p53/MDM2 ratio and in AIF release, without modifications in caspase activity or cleaved-PARP levels. Activated caspases-9 and -7 and cleaved-PARP increased significantly at 96 hr, concomitantly with a down-regulation of the Bcl-2/Bax ratio. These data suggest that two distinct apoptotic processes are triggered by melatonin in MCF-7 cells: an early, TGFbeta1 and caspase-independent response, and a late apoptotic TGFbeta1-dependent process in which activated-caspase-7 is likely to be the terminal effector.
authors.affiliation: Surgery Department "Pietro Valdoni", Rome, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Cucina
authors.forename: Sara
authors.initials: S
authors.lastname: Proietti
authors.forename: Fabrizio
authors.initials: F
authors.lastname: D'Anselmi
authors.forename: Pierpaolo
authors.initials: P
authors.lastname: Coluccia
authors.forename: Simona
authors.initials: S
authors.lastname: Dinicola
authors.forename: Luigi
authors.initials: L
authors.lastname: Frati
authors.forename: Mariano
authors.initials: M
authors.lastname: Bizzarri
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D000975:Antioxidants / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis*; D001943:Breast Neoplasms / Q000188:drug therapy / Q000378:metabolism*; D045744:Cell Line, Tumor; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D008550:Melatonin / Q000494:pharmacology*; D009363:Neoplasm Proteins / Q000378:metabolism*; D013997:Time Factors; D053773:Transforming Growth Factor beta1 / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D000975:Antioxidants; D051017:Apoptosis Regulatory Proteins; D009363:Neoplasm Proteins; D053773:Transforming Growth Factor beta1; D008550:Melatonin