Alterations in c-Myc phenotypes resulting from dynamin-related protein 1 (Drp1)-mediated mitochondrial fission

Abstract

The c-Myc (Myc) oncoprotein regulates numerous phenotypes pertaining to cell mass, survival and metabolism. Glycolysis, oxidative phosphorylation (OXPHOS) and mitochondrial biogenesis are positively controlled by Myc, with myc−/− rat fibroblasts displaying atrophic mitochondria, structural and functional defects in electron transport chain (ETC) components, compromised OXPHOS and ATP depletion. However, while Myc influences mitochondrial structure and function, it is not clear to what extent the reverse is true. To test this, we induced a state of mitochondrial hyper-fission in rat fibroblasts by de-regulating Drp1, a dynamin-like GTPase that participates in the terminal fission process. The mitochondria from these cells showed reduced mass and interconnectivity, a paucity of cristae, a marked reduction in OXPHOS and structural and functional defects in ETC Complexes I and V. High rates of abortive mitochondrial fusion were observed, likely reflecting ongoing, but ultimately futile, attempts to normalize mitochondrial mass. Cellular consequences included reduction of cell volume, ATP depletion and activation of AMP-dependent protein kinase. In response to Myc deregulation, apoptosis was significantly impaired both in the absence and presence of serum, although this could be reversed by increasing ATP levels by pharmacologic means. The current work demonstrates that enforced mitochondrial fission closely recapitulates a state of Myc deficiency and that mitochondrial integrity and function can affect Myc-regulated cellular behaviors. The low intracellular ATP levels that are frequently seen in some tumors as a result of inadequate vascular perfusion could favor tumor survival by countering the pro-apoptotic tendencies of Myc overexpression.

Respiratory Capacity and Reserve Predict Cell Sensitivity to Mitochondria Inhibitors: Mechanism-Based Markers to Identify Metformin-Responsive Cancers

“…Abundant experimental evidence suggests that downregulation of mitochondrial respiration capacity is intimately linked to the process of malignant transformation (43)(44)(45)(46). Indeed, we found that the process of transforming BJ fibroblast cells led to the reduction of RC and RR, providing direct evidence connecting malignant transformation to changes in respiratory properties, and increased vulnerability to antimitochondria agents such as metformin.…”

“…Knowledge has been growing steadily about metabolic differences between cancer cells and benign cells. Although the molecular mechanisms for the metabolic adaptation are multifaceted and likely variable in different cancer cells, several common tumor suppressors or oncogenes, such as p53 and RAS, have been linked to the regulation of glycolysis and mitochondrial activity (43)(44)(45)(46). We postulated that cancer cells have lower RC/RC than their normal counterparts as a direct consequence of the transformation process.…”

Aspirin increases mitochondrial fatty acid oxidation

“…Mitochondria were visualized with mouse anti-ATP Synthase (ThermoFisher, Clone 4.3E8.D10), peroxisomes with rabbit anti-PMP70 (Abcam), and nuclei with Hoechst Dye (Sigma), using standard techniques as described [22, 23]. Secondary antibodies used were goat anti-mouse Cy3 (Jackson Immunolaboratories) and goat anti-rabbit Alexa 488 (ThermoFisher).…”

Metabolic and oncogenic adaptations to pyruvate dehydrogenase inactivation in fibroblasts

“…S1F). This may reflect a compensatory change by which cells conserve energy through the reduction of biomass (see below) (17).…”