Fatty acid synthase inhibitors induce apoptosis in non-tumorigenic melan-a cells associated with inhibition of mitochondrial respiration

PLoS One. 2014 Jun 25;9(6):e101060. doi: 10.1371/journal.pone.0101060. eCollection 2014.

Abstract

The metabolic enzyme fatty acid synthase (FASN) is responsible for the endogenous synthesis of palmitate, a saturated long-chain fatty acid. In contrast to most normal tissues, a variety of human cancers overexpress FASN. One such cancer is cutaneous melanoma, in which the level of FASN expression is associated with tumor invasion and poor prognosis. We previously reported that two FASN inhibitors, cerulenin and orlistat, induce apoptosis in B16-F10 mouse melanoma cells via the intrinsic apoptosis pathway. Here, we investigated the effects of these inhibitors on non-tumorigenic melan-a cells. Cerulenin and orlistat treatments were found to induce apoptosis and decrease cell proliferation, in addition to inducing the release of mitochondrial cytochrome c and activating caspases-9 and -3. Transfection with FASN siRNA did not result in apoptosis. Mass spectrometry analysis demonstrated that treatment with the FASN inhibitors did not alter either the mitochondrial free fatty acid content or composition. This result suggests that cerulenin- and orlistat-induced apoptosis events are independent of FASN inhibition. Analysis of the energy-linked functions of melan-a mitochondria demonstrated the inhibition of respiration, followed by a significant decrease in mitochondrial membrane potential (ΔΨm) and the stimulation of superoxide anion generation. The inhibition of NADH-linked substrate oxidation was approximately 40% and 61% for cerulenin and orlistat treatments, respectively, and the inhibition of succinate oxidation was approximately 46% and 52%, respectively. In contrast, no significant inhibition occurred when respiration was supported by the complex IV substrate N,N,N',N'-tetramethyl-p-phenylenediamine (TMPD). The protection conferred by the free radical scavenger N-acetyl-cysteine indicates that the FASN inhibitors induced apoptosis through an oxidative stress-associated mechanism. In combination, the present results demonstrate that cerulenin and orlistat induce apoptosis in non-tumorigenic cells via mitochondrial dysfunction, independent of FASN inhibition.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis / drug effects*
  • Blotting, Western
  • Cell Cycle / drug effects
  • Cell Proliferation / drug effects
  • Cell Respiration / drug effects
  • Cells, Cultured
  • Cerulenin / pharmacology*
  • Citrate (si)-Synthase / antagonists & inhibitors
  • Cytochromes c / metabolism
  • Fatty Acid Synthases / antagonists & inhibitors*
  • Fatty Acid Synthesis Inhibitors / pharmacology*
  • Humans
  • Keratinocytes / drug effects
  • Keratinocytes / enzymology
  • Keratinocytes / pathology*
  • Melanocytes / drug effects
  • Melanocytes / enzymology
  • Melanocytes / pathology*
  • Melanoma / drug therapy
  • Melanoma / enzymology
  • Melanoma / pathology
  • Membrane Potential, Mitochondrial / drug effects*
  • Mice
  • RNA, Messenger / genetics
  • Reactive Oxygen Species / metabolism
  • Real-Time Polymerase Chain Reaction
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction
  • Spectrometry, Mass, Electrospray Ionization

Substances

  • Fatty Acid Synthesis Inhibitors
  • RNA, Messenger
  • Reactive Oxygen Species
  • Cerulenin
  • Cytochromes c
  • Fatty Acid Synthases
  • Citrate (si)-Synthase

Grants and funding

This work was supported by Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP –06/59786-0, 07/54639-1, 08/57471-7, and 11/50400-0), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq – 470539/2008-9). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.