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Cancer Lett. 2016 Sep 28;380(1):106-13. doi: 10.1016/j.canlet.2016.06.018. Epub 2016 Jun 22.

Inhibitions of mTORC1 and 4EBP-1 are key events orchestrated by Rottlerin in SK-Mel-28 cell killing.

Author information

1
Department of Life Sciences, University of Siena, via Aldo Moro 7, 53100 Siena, Italy.
2
Department of Molecular and Developmental Medicine, University of Siena, Via Aldo Moro 7, 53100 Siena, Italy.
3
Department of Biology and Evolution, University of Ferrara, Via Luigi Borsari 46, 44100 Ferrara, Italy.
4
Department of Medicine, Surgery and Neuroscience, University of Siena, Strada delle Scotte 4, 53100 Siena, Italy.
5
Department of Life Sciences, University of Siena, via Aldo Moro 7, 53100 Siena, Italy. Electronic address: emanuela.maioli@unisi.it.

Abstract

Earlier studies demonstrated that Rottlerin exerts a time- and dose-dependent antiproliferative effect on SK-Mel-28 melanoma cells during 24 h of treatment, but cytotoxicity due to cell death began only after a 48 h exposure. In the current study, in order to identify the type of cell death in this cell line, which is notoriously refractory to most anticancer therapies, and to clarify the underlying mechanisms of this delayed outcome, we searched for apoptotic, necrotic/necroptotic and autophagic traits in Rottlerin-exposed cells. Although SK-Mel-28 cells are both apoptosis and autophagy competent, Western blotting analysis, caspase activity assay, nuclear imaging and the effects of autophagy, apoptosis and necroptosis inhibitors, indicated that Rottlerin cytotoxicity was due to none of the aforementioned death mechanisms. Nevertheless, in growth arrested cells, the death did occur after a prolonged treatment and most likely ensued from the observed blockage of protein synthesis that reached levels expected to be incompatible with cell survival. From a mechanistic point of view, we ascribed this effect to the documented inhibition of mTORC1 activity; mTORC1 inhibition on the one hand led to a not deadly, rather protective autophagic response but, on the other hand caused a near complete arrest of protein synthesis. Interestingly, no cytotoxicity was found towards normal skin fibroblasts, which only resulted mildly growth arrested by the drug.

KEYWORDS:

4EBP-1; AMPK; Autophagy; Protein synthesis; Rottlerin; mTOR

PMID:
27343979
DOI:
10.1016/j.canlet.2016.06.018
[Indexed for MEDLINE]

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