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Microarray and biochemical analysis of lovastatin-induced apoptosis of squamous cell carcinomas
Jim Dimitroulakos1, Wilson H Marhin, Jason Tokunaga
1Department of Cellular and Molecular Biology, The University Health Network, 610 University Avenue, Toronto, Ontario, Canada M5G 2M9.
Abstract:
We recently identified 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme of the mevalonate pathway, as a potential therapeutic target of the head and neck squamous cell carcinomas (HNSCC) and cervical carcinomas (CC). The products of this complex biochemical pathway, including de novo cholesterol, are vital for a variety of key cellular functions affecting membrane integrity, cell signaling, protein synthesis, and cell cycle progression. Lovastatin, a specific inhibitor of HMG-CoA reductase, induces a pronounced apoptotic response in a specific subset of tumor types, including HNSCC and CC. The mediators of this response are not well established. Identification of differentially expressed genes represents a feasible approach to delineate these mediators as lovastatin has the potential to modulate transcription indirectly by perturbing levels of sterols and other mevalonate metabolites. Expression analysis following treatment of the HNSCC cell lines SCC9 or SCC25 with 10 microM lovastatin for 1 day showed that less than 2% (9 cDNAs) of the 588 cDNAs on this microarray were affected in both cell lines. These included diazepam-binding inhibitor/acyl-CoA-binding protein, the activated transcription factor 4 and rhoA. Because the biosynthesis of mevalonate leads to its incorporation into more than a dozen classes of end products, their role in lovastatin-induced apoptosis was also evaluated. Addition of the metabolites of all the major branches of the mevalonate pathway indicated that only the nonsterol moiety, geranylgeranyl pyrophosphate (GGPP), significantly inhibited the apoptotic effects of lovastatin in HNSCC and CC cells. Because rhoA requires GGPP for its function, this links the microarray and biochemical data and identifies rhoA as a potential mediator of the anticancer properties of lovastatin. Our data suggest that the depletion of nonsterol mevalonate metabolites, particularly GGPP, can be potential mediators of lovastatin-induced apoptosis of HNSCC and CC cells.
Insights
Lovastatin induces apoptosis in head and neck and cervical cancers by inhibiting HMG-CoA reductase. Depletion of geranylgeranyl pyrophosphate (GGPP), a mevalonate metabolite, mediates this effect, identifying rhoA as a key factor.
Area of Science:
- Biochemistry
- Molecular Biology
- Oncology
Background:
- 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase is a therapeutic target in head and neck squamous cell carcinomas (HNSCC) and cervical carcinomas (CC).
- The mevalonate pathway produces essential molecules like cholesterol, crucial for cellular functions.
- Lovastatin, an HMG-CoA reductase inhibitor, triggers apoptosis in HNSCC and CC, but mediators are unknown.
Purpose of the Study:
- To identify mediators of lovastatin-induced apoptosis in HNSCC and CC.
- To investigate the role of mevalonate pathway metabolites in lovastatin's anticancer effects.
- To explore the potential involvement of rhoA in lovastatin's mechanism of action.
Main Methods:
- Gene expression analysis using microarrays on HNSCC cell lines (SCC9, SCC25) treated with lovastatin.
- Biochemical assays evaluating the impact of mevalonate pathway metabolites on lovastatin-induced apoptosis.
- Correlation of gene expression data with metabolic pathway analysis.
Main Results:
- Lovastatin treatment affected less than 2% of cDNAs, including diazepam-binding inhibitor, activated transcription factor 4, and rhoA.
- Only geranylgeranyl pyrophosphate (GGPP), a nonsterol mevalonate metabolite, significantly inhibited lovastatin-induced apoptosis.
- RhoA, which requires GGPP, was identified as a potential mediator linking microarray and biochemical findings.
Conclusions:
- The depletion of nonsterol mevalonate metabolites, specifically GGPP, mediates lovastatin-induced apoptosis in HNSCC and CC.
- RhoA activation, dependent on GGPP, is implicated in the anticancer properties of lovastatin.
- Targeting the mevalonate pathway, particularly GGPP synthesis, offers a potential therapeutic strategy for HNSCC and CC.