title: Regulation of succinate-ubiquinone reductase and fumarate reductase activities in human complex II by phosphorylation of its flavoprotein subunit.
abstract: Complex II (succinate-ubiquinone reductase; SQR) is a mitochondrial respiratory chain enzyme that is directly involved in the TCA cycle. Complex II exerts a reverse reaction, fumarate reductase (FRD) activity, in various species such as bacteria, parasitic helminths and shellfish, but the existence of FRD activity in humans has not been previously reported. Here, we describe the detection of FRD activity in human cancer cells. The activity level was low, but distinct, and it increased significantly when the cells were cultured under hypoxic and glucose-deprived conditions. Treatment with phosphatase caused the dephosphorylation of flavoprotein subunit (Fp) with a concomitant increase in SQR activity, whereas FRD activity decreased. On the other hand, treatment with protein kinase caused an increase in FRD activity and a decrease in SQR activity. These data suggest that modification of the Fp subunit regulates both the SQR and FRD activities of complex II and that the phosphorylation of Fp might be important for maintaining mitochondrial energy metabolism within the tumor microenvironment.
authors: Cancer Physiology Project, Investigative Treatment Division, National Cancer Center Research Institute East, Chiba, Japan. etomitsu@east.ncc.go.jp
authors: Eriko
authors: E
authors: Tomitsuka
authors: Kiyoshi
authors: K
authors: Kita
authors: Hiroyasu
authors: H
authors: Esumi
mesh_terms: D000818:Animals; D018929:Cell Culture Techniques; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D042963:Electron Transport Complex II / Q000737:chemistry* / Q000378:metabolism*; D005420:Flavoproteins / Q000378:metabolism*; D005947:Glucose / Q000172:deficiency; D006801:Humans; D008928:Mitochondria / Q000201:enzymology; D010744:Phosphoric Monoester Hydrolases / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011494:Protein Kinases / Q000494:pharmacology; D021122:Protein Subunits / Q000378:metabolism*; D013385:Succinate Dehydrogenase / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D005420:Flavoproteins; D021122:Protein Subunits; D042963:Electron Transport Complex II; D013385:Succinate Dehydrogenase; D011494:Protein Kinases; D010744:Phosphoric Monoester Hydrolases; D005947:Glucose