Activation of the Integrated Stress Response Regulates Lovastatin-induced Apoptosis

Abstract

Lovastatin, a potent inhibitor of mevalonate synthesis, can readily induce apoptosis in a subset of human tumor types including head and neck squamous cell carcinomas (HNSCC). We recently identified activation of transcription factor (ATF) 4 as a lovastatin induced gene in HNSCC cells. ATF4 plays a significant role in regulating cellular responses to a wide variety of stress inducers known as the integrated stress response (ISR). These cell stresses lead to the phosphorylation of eukaryotic initiation factor (eIF) 2␣ shutting down global protein translation. However, the translation of ATF4 is enhanced. In this study, lovastatin treatment induced eIF2␣ phosphorylation and inhibited global protein translation. ATF4 expression was induced followed by increased ATF3 and CHOP expression, targets of ATF4 activity, in SCC25 HNSCC cells. In CHOP ؊/؊ murine embryonic fibroblasts (MEFs), lovastatin-induced apoptosis was attenuated indicating a role for CHOP in this response. Furthermore, the eIF2␣ kinase GCN2 mediates lovastatin induction of ATF4 and lovastatin-induced apoptosis was also attenuated in GCN2 ؊/؊ MEFs. The pro-drug version of lovastatin has potential proteasome inhibitory activity and recently a variety of well established proteasome inhibitors were shown to activate the ISR. In this study, neither the pro-drug nor the active forms of lovastatin had any significant effect on proteasome activity. Therefore, lovastatin, by targeting mevalonate synthesis, is a potent inducer of the ISR through a novel and as yet unrecognized mechanism.

Lovastatin inhibits EGFR dimerization and AKT activation in squamous cell carcinoma cells: potential regulation by targeting rho proteins

“…We next performed quantitative reverse transcriptase PCR analysis to compare the expression profile of (activation of transcription factor) ATF3 and GAPDH (Figure 3b) mRNA in monosome-and polysome-enriched fractions. It has been shown before that increased ATF3 expression is an indication of attenuation of protein translation during stress (Niknejad et al, 2007). We found that ATF3 mRNA (Figure 3b) shifted toward the heavier polysome fractions in lovastatin-treated cells.…”

“…Using EGFR-targeting agents requires combination-based therapies to enhance their clinical activity. Our recent studies have shown that the depletion of mevalonate metabolites affects the activity of a number of cell signaling cascades, including inhibitory effects on EGFR activity and their downstream signaling pathways (Mantha et al, 2005;Niknejad et al, 2007). Combinations of statins with agents targeting EGFR activity, such as gefitinib, induce a potent synergistic cytotoxic response in a variety of responsive tumor types, including SCC (Mantha et al, 2005).…”

Peroxisome Deficiency Causes a Complex Phenotype because of Hepatic SREBP/Insig Dysregulation Associated with Endoplasmic Reticulum Stress

“…Therefore, levels of other mevalonate metabolites may also be perturbed in PEX2 Ϫ/Ϫ mice leading to an activation of PERK and/or GCN2. For instance, inhibition of cholesterol biosynthesis can trigger the ISR, probably because of alterations of membrane cholesterol composition (56,57). Perturbations of non-sterol isoprenoids downstream of the farnesyl pyrophosphate branch point also contribute to the development of ER stress.…”

Monensin Inhibits Epidermal Growth Factor Receptor Trafficking and Activation: Synergistic Cytotoxicity in Combination with EGFR Inhibitors

“…The synergistic effects of lovastatin in combination with EGFR-TKIs that we previously reported were due to its ability to inhibit EGFR activity (30) and to induce the integrated stress response; particularly, the ATF3 that regulates the apoptosis induction of this pathway (35,36). We first evaluated the effect of monensin treatment alone and in combination with erlotinib on ligand-induced EGFR activation and its downstream signaling pathways by Western blot analysis.…”