Inhibition of fatty acid synthase (FAS) suppressesHER2/neu(erbB-2) oncogene overexpression in cancer cells

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Abstract
Fatty acid synthase (FAS) activity is a potential therapeutic target to treat cancer and obesity. Here, we have identified a molecular link between FAS andHER2(erbB-2) oncogene, a marker for poor prognosis that is overexpressed in 30% of breast and ovarian cancers. Pharmacological FAS inhibitors cerulenin and C75 were found to suppress p185HER2oncoprotein expression and tyrosine-kinase activity in breast and ovarianHER2overexpressors. Similarly, p185HER2expression was dramatically down-regulated when FAS gene expression was silenced by using the highly sequence-specific mechanism of RNA interference (RNAi). Pharmacological and RNAi-mediated silencing of FAS specifically down-regulatedHER2mRNA and, concomitantly, caused a prominent up-regulation of PEA3, a transcriptional repressor ofHER2. A cytoplasmic redistribution of p185HER2was associated with marked morphological changes of FAS RNAi-transfected cells, whereas chemical inhibitors of FAS promoted a striking nuclear accumulation of p185HER2. The simultaneous targeting of FAS andHER2by chemical FAS inhibitors and the humanized antibody directed against p185HER2trastuzumab, respectively, was synergistically cytotoxic towardHER2overexpressors. Similarly, concurrent RNAi-mediated silencing of FAS andHER2genes synergistically stimulated apoptotic cell death inHER2overexpressors. p185HER2was synergistically down-regulated after simultaneous inhibition of FAS andHER2by either pharmacological inhibitors or small interfering RNA. These findings provide evidence of an active role of FAS in cancer evolution by specifically regulating oncogenic proteins closely related to malignant transformation, strongly suggesting thatHER2oncogene may act as the key molecular sensor of energy imbalance after the perturbation of tumor-associated FAS hyperactivity in cancer cells.