title: Involvement of Bax protein in the prevention of glucocorticoid-induced thymocytes apoptosis by melatonin.
abstract: The antiapoptotic effect of melatonin has been described in several systems. In this study, the antagonistic effect of the methoxyindole on dexamethasone-induced apoptosis in mouse thymocytes was examined. Melatonin decreased both DNA fragmentation, and the number of annexin V-positive cells incubated in the presence of dexamethasone. Analysis of the expression of the members of the Bcl-2 family indicated that the synthetic glucocorticoid increased Bax protein levels without affecting the levels of Bcl-2, Bcl-XL, Bcl-XS, or Bak. This effect correlated with an increase in thymocytes bax mRNA levels. Dexamethasone also increased the release of cytochrome C from mitochondria. All of these effects were reduced in the presence of melatonin, which was ineffective per se on these parameters. In addition, the involvement of cAMP on glucocorticoid/melatonin antagonism was examined. Both melatonin and dexamethasone decreased the levels of this nucleotide in mouse thymocytes, indicating that the antagonistic action between both hormones involves a cAMP-independent pathway. In summary, the present results suggest that the antiapoptotic effect of melatonin on glucocorticoid-treated thymocytes would be a consequence of an inhibition of the mitochondrial pathway, presumably through the regulation of Bax protein levels.
mesh_terms: D000276:Adjuvants, Immunologic / Q000494:pharmacology*; D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D045304:Cytochromes c / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology; D008297:Male; D008550:Melatonin / Q000494:pharmacology*; D051379:Mice; D008815:Mice, Inbred Strains; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger / Q000032:analysis; D011965:Receptors, Glucocorticoid / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology* / Q000378:metabolism; D051028:bcl-2-Associated X Protein
chemical_list: D000276:Adjuvants, Immunologic; C494827:Bax protein, mouse; D005938:Glucocorticoids; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D051028:bcl-2-Associated X Protein; D003907:Dexamethasone; D045304:Cytochromes c; D008550:Melatonin