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Inhibitions of mTORC1 and 4EBP-1 are key events orchestrated by Rottlerin in SK-Mel-28 cell killing
E Daveri1, E Maellaro2, G Valacchi3
1Department of Life Sciences, University of Siena, via Aldo Moro 7, 53100 Siena, Italy.
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.
Insights
Rottlerin causes melanoma cell death by blocking protein synthesis, not apoptosis or autophagy. This delayed cytotoxicity in SK-Mel-28 cells is linked to mTORC1 inhibition, offering a novel therapeutic insight.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Death Mechanisms
Background:
- Rottlerin exhibits time- and dose-dependent antiproliferative effects on SK-Mel-28 melanoma cells.
- Cytotoxicity in SK-Mel-28 cells, a therapy-refractory line, is delayed, appearing after 48 hours of Rottlerin exposure.
- Previous studies indicated antiproliferative effects but lacked clarity on the specific cell death pathways involved.
Purpose of the Study:
- To identify the precise type of cell death induced by Rottlerin in SK-Mel-28 melanoma cells.
- To elucidate the underlying molecular mechanisms responsible for the delayed cytotoxicity observed.
- To investigate the role of apoptosis, necroptosis, and autophagy in Rottlerin-induced cell death.
Main Methods:
- Analysis of apoptotic, necrotic/necroptotic, and autophagic markers in Rottlerin-treated SK-Mel-28 cells.
- Western blotting, caspase activity assays, and nuclear imaging were employed.
- Assessment of Rottlerin's effects in the presence of specific inhibitors for apoptosis, autophagy, and necroptosis.
Main Results:
- Rottlerin-induced cytotoxicity in SK-Mel-28 cells was not mediated by apoptosis, necroptosis, or autophagy.
- Prolonged Rottlerin treatment led to growth arrest and significant inhibition of protein synthesis.
- This inhibition of protein synthesis was linked to the suppression of mTORC1 activity, which also triggered a protective autophagic response.
Conclusions:
- Rottlerin induces melanoma cell death through a novel mechanism involving the blockage of protein synthesis, independent of classical cell death pathways.
- The observed effects are attributed to mTORC1 inhibition, highlighting its dual role in protein synthesis arrest and autophagy induction.
- Rottlerin demonstrates selective toxicity, arresting growth in normal fibroblasts without causing significant cytotoxicity, suggesting potential therapeutic applications.
