Inhibition of the mevalonate pathway affects epigenetic regulation in cancer cells

Abstract

The mevalonate pathway provides metabolites for post-translational modifications such as farnesylation, which are critical for the activity of RAS downstream signaling. Subsequently occurring regulatory processes can induce an aberrant stimulation of DNA methyltransferase (DNMT1) as well as changes in histone deacetylases (HDACs) and microRNAs in many cancer cell lines. Inhibitors of the mevalonate pathway are increasingly recognized as anticancer drugs. Extensive evidence indicates an intense cross-talk between signaling pathways, which affect growth, differentiation, and apoptosis either directly or indirectly via epigenetic mechanisms. Herein, we show data obtained by novel transcriptomic and corresponding methylomic or proteomic analyses from cell lines treated with pharmacologic doses of respective inhibitors (i.e., simvastatin, ibandronate). Metabolic pathways and their epigenetic consequences appear to be affected by a changed concentration of NADPH. Moreover, since the mevalonate metabolism is part of a signaling network, including vitamin D metabolism or fatty acid synthesis, the epigenetic activity of associated pathways is also presented. This emphasizes the far-reaching epigenetic impact of metabolic therapies on cancer cells and provides some explanation for clinical observations, which indicate the anticancer activity of statins and bisphosphonates.

Keywords: Mevalonate pathway; bisphosphonates; cancer metabolism; epigenetics; statins.

Figure 1

Inhibition of the mevalonate pathway influences the stability of the plasma membrane. It inhibits isoprenylation of the small GTP-binding proteins and, therefore, the activity of RAS signaling. As a consequence, RAS signals via RAF into the MAPK pathway, an inhibited signaling via FLI1 and JNK (c-JUN N-terminal kinase), leads to a downregulation of DNMT1. The cross-talk of RAS with PI3K-AKT-mTOR signaling influences the expression of HDACs. Additional metabolic pathways influenced by RAS signaling are glucose uptake and the OCM, which may both be fueled by activating mutations of the P53 gene (TP53) and play essential roles in DNA repair and inflammation. Similar to the inhibition of HMG-Co-A reductase, a downregulation of these pathways changes the concentration of NADPH. In addition, there is also a downregulation of the RHOA-ROCK signaling and the associated vitamin D degrading enzyme CYP24A1 . This could induce a series of vitamin D−associated effects on fatty acid metabolism and epigenetics, for example .

Figure 2

NAD(P)⁺ biosynthesis and major NAD(P)⁺-mediated signaling pathways affect histone (de)acetylation (modified according to (36)). Simvastatin and ibandronate induce upregulation of the NMNAT (nicotineamide mononucleotide acetyltransferase), which synthesizes NAD from ATP and NMN (nicotineamide mononucleotide). NAD⁺-consuming reactions from PARP (polyADP ribose polymerase), HDACs, and sirtuins are downregulated by inhibitors of mevalonate synthesis in cancer cells.

Figure 3

Results from a transcriptomic analysis of the OCM: Downregulated genes were, dependening on their level colored in green, upregulated in red. The analyzed cell lines are from the left to the right: U2OS osteosarcoma treated with ibandronate and simvastatin; PC-3 prostate cancer cells treated with ibandronate. The labels are the actual gene names according to the NCBI gene database. Abbreviations: MTHFD, methylenetetrahydrofolate dehydrogenase; MTHFR, methylenetetrahydrofolate reductase; DHFR, dihydrofolate reductase; TYMS, thymidylate synthetase; SHMT, serine hydroxymethyltransferase; AHCYL1, adenosylhomocysteinase-like 1; MTR, 5-methyltetrahydrofolate-homocysteine methyltransferase; DNMT1, DNA (cytosine-5-)-methyltransferase 1; MAT2B, methionine adenosyltransferase II, beta.

Figure 4

Effect of a FASN inhibitor (C75) or vitamin D3 on epigenetic regulators (DNMT1 and HDAC2, key enzymes of OCM DHFR and TYMS, as well as FASN.