Frontiers in Bioscience-Elite (FBE) is published by IMR Press from Volume 13 Issue 2 (2021). Previous articles were published by another publisher on a subscription basis, and they are hosted by IMR Press on imrpress.com as a courtesy and upon agreement with Frontiers in Bioscience.
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Academic Editor: Anna Czarnecka
Oncocytic tumors, also called oxyphilic tumors, are characterized by hyperproliferation of mitochondria, which histologically presents as a fine granular eosinophilic cytoplasm. In accordance with the high mitochondrial density in oncocytomas, transcript levels of subunits of complexes of the oxidative phosphorylation (OXPHOS) system are increased. Hence, for a long time oncocytomas were presumed to have a highly active aerobic mitochondrial energy metabolism. Recently, detailed analysis of all OXPHOS complexes in a variety of oncocytomas revealed loss of complex I and compensatory up-regulation of the other complexes. In half of the oncocytoma cases examined the absence of complex I is caused by disruptive mutations in mitochondrial DNA encoding complex I subunits. The new data presented here on rare oncocytomas and the accompanying review of the literature clearly indicate that complex I deficiency in combination with up-regulation of mitochondria can be regarded as a hallmark of oncocytic tumor cells. Therefore, complex I of the respiratory chain has to be added to the growing list of mitochondrial tumor suppressors.