title: Involvement of mitophagy in oncogenic K-Ras-induced transformation: overcoming a cellular energy deficit from glucose deficiency.
abstract: Although mitochondrial impairment has often been implicated in carcinogenesis, the mechanisms of its development in cancer remain unknown. We report here that autophagy triggered by oncogenic K-Ras mediates functional loss of mitochondria during cell transformation to overcome an energy deficit resulting from glucose deficiency. When Rat2 cells were infected with a retrovirus harboring constitutively active K-Ras (V12) , mitochondrial respiration significantly declined in parallel with the acquisition of transformation characteristics. Decreased respiration was not related to mitochondrial biogenesis but was inversely associated with the increased formation of acidic vesicles enclosing mitochondria, during which autophagy-related proteins such as Beclin 1, Atg5, LC3-II and vacuolar ATPases were induced. Interestingly, blocking autophagy with conventional inhibitors (bafilomycin A, 3-methyladenin) and siRNA-mediated knockdown of autophagy-related genes recovered respiratory protein expression and respiratory activity; JNK was involved in these phenomena as an upstream regulator. The cells transformed by K-Ras (V12)  maintained cellular ATP level mainly through glycolytic ATP production without induction of GLUT1, the low Km glucose transporter. Finally, K-Ras (V12) -triggered LC3-II formation was modulated by extracellular glucose levels, and LC3-II formation increased only in hepatocellular carcinoma tissues exhibiting low glucose uptake and increased K-Ras expression. Taken together, our observations suggest that mitochondrial functional loss may be mediated by oncogenic K-Ras-induced mitophagy during early tumorigenesis even in the absence of hypoxia, and that this mitophagic process may be an important strategy to overcome the cellular energy deficit triggered by insufficient glucose.
authors: Department of Biochemistry and Molecular Biology, The Graduate School, Ajou University, Suwon, South Korea.
authors: June-Hyung
authors: JH
authors: Kim
authors: Hee Young
authors: HY
authors: Kim
authors: Young-Kyoung
authors: YK
authors: Lee
authors: Young-Sil
authors: YS
authors: Yoon
authors: Wei Guang
authors: WG
authors: Xu
authors: Joon-Kee
authors: JK
authors: Yoon
authors: Sung-E
authors: SE
authors: Choi
authors: Young-Gyu
authors: YG
authors: Ko
authors: Min-Jung
authors: MJ
authors: Kim
authors: Su-Jae
authors: SJ
authors: Lee
authors: Hee-Jung
authors: HJ
authors: Wang
authors: Gyesoon
authors: G
authors: Yoon
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D000368:Aged; D000818:Animals; D001343:Autophagy; D001692:Biological Transport; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D002471:Cell Transformation, Neoplastic; D015972:Gene Expression Regulation, Neoplastic; D011905:Genes, ras; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D000860:Hypoxia; D008875:Middle Aged; D008928:Mitochondria / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D051381:Rats; D014617:Vacuoles / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D034741:RNA, Small Interfering; D000255:Adenosine Triphosphate; D000251:Adenosine Triphosphatases; D018631:ras Proteins; D005947:Glucose