Abstract
BackgroundApoptosis-inducing factor (AIF), named for its involvement in cell death pathways, is a mitochondrial protein that regulates metabolic homeostasis. In addition to supporting the survival of healthy cells, AIF also plays a contributory role to the development of cancer through its enzymatic activity, and we have previously shown that AIF preferentially supports advanced-stage prostate cancer cells. Here we further evaluated the role of AIF in tumorigenesis by exploring its function in pancreatic cancer, a disease setting that most often presents at an advanced stage by the time of diagnosis.MethodsA bioinformatics approach was first employed to investigate AIF mRNA transcript levels in pancreatic tumor specimens vs. normal tissues. AIF-deficient pancreatic cancer cell lines were then established via lentiviral infection. Immunoblot analysis was used to determine relative protein quantities within cells. Cell viability was measured by flow cytometry; in vitro and Matrigel™ growth/survival using Coulter™ counting and phase contrast microscopy; and glucose consumption in the absence and presence of Matrigel™ using spectrophotometric methods.ResultsArchival gene expression data revealed a modest elevation of AIF transcript levels in subsets of pancreatic tumor specimens, suggesting a possible role in disease progression. AIF expression was then suppressed in a panel of five pancreatic cancer cell lines that display diverse metabolic phenotypes. AIF ablation selectively crippled the growth of cells in vitro in a manner that directly correlated with the loss of mitochondrial respiratory chain subunits and altered glucose metabolism, and these effects were exacerbated in the presence of Matrigel™ substrate. This suggests a critical metabolic role for AIF to pancreatic tumorigenesis, while the spectrum of sensitivities to AIF ablation depends on basal cellular metabolic phenotypes.ConclusionsAltogether these data indicate that AIF supports the growth and survival of metabolically defined pancreatic cancer cells and that this metabolic function may derive from a novel mechanism so far undocumented in other cancer types.
Highlights
Apoptosis-inducing factor (AIF), named for its involvement in cell death pathways, is a mitochondrial protein that regulates metabolic homeostasis
The AIFdeficient phenotype is associated with concomitant depletions of mitochondrial respiratory chain subunits and subsequent impairment of oxidative phosphorylation [22], in part due to a resulting defective co-translational import system regulated by the AIF-interacting protein CHCHD4/MIA40 [23, 24]
Materials MEM, DMEM, RPMI 1640, DMEM/F12, GlutaMAX, horse serum, insulin, transferrin, epidermal growth factor, trypsin, 4–12 % bis-tris polyacrylamide gels, and nitrocellulose membranes were obtained from Life Technologies; fetal bovine serum (FBS), phosphate buffered saline (PBS), and Pierce ECL 2 Western Blotting Substrate were from Thermo Scientific; QuantiChromTM Glucose Assay Kit was from BioAssay Systems; MatrigelTM was from BD Biosciences; Matrigel Recovery Solution was from Corning; protease inhibitor tablets were from Roche Applied Science; all other materials were from Sigma
Summary
Apoptosis-inducing factor (AIF), named for its involvement in cell death pathways, is a mitochondrial protein that regulates metabolic homeostasis. It has been proposed that AIF functions in vivo as a metabolic sensor [25], supported by its contributory roles to disorders involving metabolic dysregulation including obesity, diabetes, and cancer [26,27,28]. While largely descriptive, these studies altogether illustrate a role for AIF as a critical regulator of cellular metabolism
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