Lovastatin‐induced apoptosis is mediated by activating transcription factor 3 and enhanced in combination with salubrinal

Abstract

We have previously demonstrated the ability of lovastatin, a potent inhibitor of mevalonate synthesis, to induce tumorspecific apoptosis. The apoptotic effects of lovastatin were regulated in part by the integrated stress response (ISR) that regulates cellular responses to a wide variety of stress inducers. A key regulator of the ISR apoptotic response is activating transcription factor 3 (ATF3) and its target gene CHOP=GADD153. In our study, we demonstrate that in multiple lovastatinresistant clones of the squamous cell carcinoma (SCC) cell line SCC9, lovastatin treatment (1-25 lM, 24 hr) in contrast to the parental line failed to significantly induce ATF3 expression. Furthermore, the SCC-derived cell lines SCC25 and HeLa that are sensitive to lovastatin-induced apoptosis also preferentially induce ATF3 expression compared to resistant breast (MCF-7) and prostate carcinoma (PC3)-derived cell lines. In HeLa cells shRNA targeting ATF3 expression as well as in ATF3-deficient murine embryonic fibroblasts, lovastatin-induced cytotoxicity and apoptosis were attenuated. In ex vivo HNSCC tumors, lovastatin also induced ATF3 mRNA expression in two of four tumors evaluated. Salubrinal, an agent that can sustain the activity of a key regulator of the ISR eIF2a, further increased the expression of ATF3 and demonstrated synergistic cytotoxicity in combination with lovastatin in SCC cells. Taken together, our results demonstrate preferential induction of ATF3 in lovastatin-sensitive tumor-derived cell lines that regulate lovastatin-induced apoptosis. Importantly, combining lovastatin with salubrinal enhanced ATF3 expression and induced synergistic cytotoxicity in SCC cells.Deregulated or elevated activity of 3-hydroxy-3-methyl glutaryl coenzyme A (HMG-CoA) reductase, the initial and rate-limiting enzyme of the mevalonate pathway, has been shown in a range of different tumors.

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

“…6C) and analyzed by qRT-PCR performed in triplicate. In our previous studies using lovastatin treatments, HMGCoA reductase induction was generally to a lower extent than ATF3 (29,35).…”

“…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.…”

Lovastatin lowers the risk of breast cancer: a population-based study using logistic regression with a random effects model

“…Increasing evidence has revealed that statins have another valuable effect in preventing cancer (Boudreau et al 2007; Jafari et al 2013; Ahern et al 2014). Various laboratory studies have demonstrated the statin-induced apoptosis of cancer cells, including breast cancer cells, with increasing evidence accumulating on the mechanism underlying this (Campbell et al 2006; Corsini et al 1995; Dimitroulakos et al 2001; Niknejad et al 2007; Woditschka et al 2010; Ma et al 2012; Niknejad et al 2014). Preclinical findings favor the possibility that lovastatin exerts anticancer effects, including effects against breast cancer.…”

“…Niknejad et al identified transcription factors that play a crucial role in lovastatin-induced apoptosis in head and neck squamous cell carcinoma cell lines (Niknejad et al 2007), and multiple stress pathways were found to regulate the cytotoxic effects of lovastatin in squamous cell carcinoma cell lines (Ma et al 2012). Another study reported that certain substances enhanced lovastatin-induced apoptosis (Niknejad et al 2014). It has been shown that lovastatin inhibited cell invasion and cell proliferation in breast cancer cell lines (Kang et al 2009; Klawitter et al 2010).…”

Activating Transcription Factor 3-mediated Chemo-intervention with Cancer Chemokines in a Noncanonical Pathway under Endoplasmic Reticulum Stress

“…Enhanced ATF3 production can be associated with cellular defenses by maintaining epithelial sur- vival after toxic insults (59). Although many reports have suggested that ATF3 has apoptosis-promoting effects (60,61), it can also protect cells from physical and chemical cytotoxic stresses by suppressing the induction of cell death factors such as p53 proteins (62). ATF3-suppressed cells show an enhanced level of p53 that probably makes the cells more sensitive to cytotoxic effects.…”