MITOCHONDRIAL PROTEINS AS TUMOR MARKERS AND ANTI-CANCER DRUG TARGETS
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AbstractCancer is a major cause of morbidity and mortality. Identification and characterization of novel biomarkers are expected to facilitate early diagnosis and improve prognosis of human malignancies. Increasing number of studies have linked tumor progression with metabolic reprogramming. However, the players involved are not fully discovered. Therefore, understanding the cancer cell plasticity may offer a successful approach for an anti-cancer strategy. In this regard, we report the functional characterization of Coiled-coil Helix Tumor and Metabolism 1 (CHTM1) and KM1 as important regulator of cancer cell metabolism.CHTM1 is localized in cytosol and mitochondrial inter-membrane spaceand regulates mitochondrial activity. Our results demonstrate that MIA40 appears to alterCHTM1 mitochondrial localizationand stability. Further, CHTM1 cysteineresiduesinvolved in CHTM1 folding modulatescellular distributionof CHTM1. Importantly, alterations in CHTM1 expression in cancer cells affect mitochondrial activity. Given thatmitochondria play an important role in cellular response to nutrient stress, we sought to analyze the role of CHTM1 in glucose/glutamine-deprived conditions. Wehave found thatCHTM1 deficiency enhancescancer cell sensitivityto glucose/glutamine starvation and metformin treatment. Additionally, increased sensitivity of CHTM1-deficient cells to metabolic stress could be in part due to inability to activate fatty acid oxidation. Further, targeting CHTM1 expression in cancer cells reduce fatty acid oxidation causing decrease in substrate availability under metabolic stress conditions. This can explain the increase in autophagy and protein catabolism in CHTM1-deficient cancer cells under metabolic stress conditions. Mechanistic studies suggest that CHTM1-mediated alterations in cancer cell metabolism under stress conditions involve modulation of PGC1 alpha-CREB-PKC signaling.We further demonstrate that under metabolic stress, CHTM1 deficiency activates p38-AIF1pathway leading to increased cell death. CHTM1 negatively regulates p38 and interacts with AIF1 alteringAIF1release frommitochondria under metabolic stress conditions.These findings are highly significant because alterations in cancer cell metabolism are linked to pathogenesis of cancer. Most importantly, multiple human malignancies associated with breast, colon and lung tissuesshow increase in CHTM1 expression. CHTM1 appears to be a high value tumor marker, that has the potential tofacilitate earlydiagnosis of human malignancies and could also serve as a target to develop novel therapeutics to manage human malignancies. In the second part of this manuscript, we report the characterization of a novel protein temporarily named as KM1. Our results indicate that KM1 is localized inthemitochondrial inner membrane and regulates mitochondrial activity. Metabolic stress-induced increased cell death is noted in KM1 knockout cancer cells, a finding consistent with the defective mitochondria in KM1-deficient cells. Our results further demonstrate that under metabolic stress KM1 regulates mitochondrial-mediated cell death. Most importantly, KM1 levels are upregulated in breast and lung cancer tissues.Collectively, our results suggest that CHTM1 and KM1 are novel proteins and are involved in regulating cancer cell metabolism.
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