Reactive Oxygen Species-generating Mitochondrial DNA Mutation Up-regulates Hypoxia-inducible Factor-1α Gene Transcription via Phosphatidylinositol 3-Kinase-Akt/Protein Kinase C/Histone Deacetylase Pathway

Abstract

Lewis lung carcinoma-derived high metastatic A11 cells constitutively overexpress hypoxia-inducible factor (HIF)-1␣ mRNA compared with low metastatic P29 cells. Because A11 cells exclusively possess a G13997A mutation in the mitochondrial NADH dehydrogenase subunit 6 (ND6) gene, we addressed here a causal relationship between the ND6 mutation and the activation of HIF-1␣ transcription, and we investigated the potential mechanism. Using trans-mitochondrial cybrids between A11 and P29 cells, we found that the ND6 mutation was directly involved in HIF-1␣ mRNA overexpression. Stimulation of HIF-1␣ transcription by the ND6 mutation was mediated by overproduction of reactive oxygen species (ROS) and subsequent activation of phosphatidylinositol 3-kinase (PI3K)-Akt and protein kinase C (PKC) signaling pathways. The up-regulation of HIF-1␣ transcription was abolished by mithramycin A, an Sp1 inhibitor, but luciferase reporter and chromatin immunoprecipitation assays indicated that Sp1 was necessary but not sufficient for HIF-1␣ mRNA overexpression in A11 cells. On the other hand, trichostatin A, a histone deacetylase (HDAC) inhibitor, markedly suppressed HIF-1␣ transcription in A11 cells. In accordance with this, HDAC activity was high in A11 cells but low in P29 cells and in A11 cells treated with the ROS scavenger ebselene, the PI3K inhibitor LY294002, and the PKC inhibitor Ro31-8220. These results suggest that the ROS-generating ND6 mutation increases HIF-1␣ transcription via the PI3K-Akt/ PKC/HDAC pathway, leading to HIF-1␣ protein accumulation in hypoxic tumor cells.

Time- and oxygen-dependent expression and regulation of NDRG1 in human brain cancer cells

“…Most of the transcription factors regulating metabolic events in cancer, including HIF-1α, have a binding site for SP1 in their promoter region (66). HIF-1α expression has been shown to be SP1-dependent in human prostate cancer cells (67), suggesting a crucial regulatory role in cancer metabolism as well as during hypoxia. We showed an upregulation of CEBPα in human GBM cells in response to hypoxia.…”

Mitochondrial genome instability in colorectal adenoma and adenocarcinoma

“…Statistical analysis revealed that fusion and fission (p= 0.0472) and mitochondrial localization genes subsets (p=0.0231) were more affected in adenocarcinoma samples. b Relative mtDNA copy number analysis showed a decreased number of mitochondrial genome content in adenocarcinoma when compared to normal colon (p=0.0092) mutated in tumors [39,32], and those mutations were associated with cancer progression mediated by ROS production, PI3K/Akt/PKC pathway activation, and HIF1α [14,13,31,40].…”

Oxidative stress and metal carcinogenesis

“…ROS induce the release of calcium from intracellular stores resulting in the activation of PKC. The activation of PKC is also required for generating ROS as well as for the ROS-mediated migration of cells [222] and HIF-1a activation [223]. Thus, uncontrolled activation of PKC is a potential mechanism of metal and/or ROS-induced carcinogenesis.…”