ALTERATIONS IN F-ACTIN DISTRIBUTION IN CELLS TREATED WITH MELATONIN

One of the possible pathways of action of melatonin is its effect on t he cytoskeleton. In this work we looked for alterations in the cytoske leton of cells treated with melatonin at physiological concentrations. T-47D, Hs-578T (human breast carcinoma cell lines), and MDCK (normal dog kidney) cells were maintained in MCDB 153 supplemented with 1% fet al bovine serum (FBS), or in Dulbecco's modified Eagle's medium (DMEM) supplemented with 5% FBS and treated with melatonin (10(-9) M or 10(- 10) M) for 2 and 5 days, with or without 10(-8) M estradiol. F-actin w as stained with phalloidin-fluorescein isothiocyanate (FITC). Cytokera tin 19 and beta-tubulin filaments were detected with specific monoclon al antibodies and secondary antibodies bound to FITC. Melatonin-treate d T-47D cells observed in a transmission electronic microscope (TEM) s howed an irregular nuclear shape and intermediate filaments disposed a round the nucleus, which was not observed in control cells. Immunofluo rescence analysis of cytokeratin filaments did not show significant di fferences between their distribution in control and treated cells. Mel atonin did not induce significant alterations in cytokeratin filaments of T-47D, Hs578T or MDCK cells in DMEM and MCDB 153, or T-47D cells i n DMEM. Melatonin induced the derangement of F-actin both in T-47D and MDCK cells kept in MCDB 153. The same was not observed when estradiol was also present. We did not observe significant alterations in the d istribution of F-actin in T-47D or Hs-578T cells grown in DMEM. In DME M, melatonin-treated MDCK cells were more elongated, with a slight con centration of F-actin on the cell boundary. Melatonin induced very sli ght alterations in microtubule organization of all cell lines studied.