Cytochrome c oxidase is activated by the oncoprotein Ras and is required for A549 lung adenocarcinoma growth.
BACKGROUND
Constitutive activation of Ras in immortalized bronchial epithelial cells increases electron transport chain activity, oxygen consumption and tricarboxylic acid cycling through unknown mechanisms. We hypothesized that members of the Ras family may stimulate respiration by enhancing the expression of the Vb regulatory subunit of cytochrome c oxidase (COX).


RESULTS
We found that the introduction of activated H-Ras(V12) into immortalized human bronchial epithelial cells increased eIF4E-dependent COX Vb protein expression simultaneously with an increase in COX activity and oxygen consumption. In support of the regulation of COX Vb expression by the Ras family, we also found that selective siRNA-mediated inhibition of K-Ras expression in A549 lung adenocarcinoma cells reduced COX Vb protein expression, COX activity, oxygen consumption and the steady-state concentration of ATP. We postulated that COX Vb-mediated activation of COX activity may be required for the anchorage-independent growth of A549 cells as soft agar colonies or as lung xenografts. We transfected the A549 cells with COX Vb small interfering or shRNA and observed a significant reduction of their COX activity, oxygen consumption, ATP and ability to grow in soft agar and as poorly differentiated tumors in athymic mice.


CONCLUSIONS
Taken together, our findings indicate that the activation of Ras increases COX activity and mitochondrial respiration in part via up-regulation of COX Vb and that this regulatory subunit of COX may have utility as a Ras effector target for the development of anti-neoplastic agents.
Molecular Targets Program, James Graham Brown Cancer Center, University of Louisville, Louisville, KY, USA.
Sucheta
S
Telang
Kristin K
KK
Nelson
Deanna L
DL
Siow
Abdullah
A
Yalcin
Joshua M
JM
Thornburg
Yoannis
Y
Imbert-Fernandez
Alden C
AC
Klarer
Hanan
H
Farghaly
Brian F
BF
Clem
John W
JW
Eaton
Jason
J
Chesney
D000230:Adenocarcinoma / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D000077192:Adenocarcinoma of Lung; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000502:physiology; D003576:Electron Transport Complex IV / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D039561:Eukaryotic Initiation Factor-4E / Q000378:metabolism; D005260:Female; D006801:Humans; D008175:Lung Neoplasms / Q000737:chemistry / Q000201:enzymology* / Q000235:genetics; D051379:Mice; D008819:Mice, Nude; D010101:Oxygen Consumption; D034741:RNA, Small Interfering / Q000235:genetics; D014183:Transplantation, Heterologous; D018631:ras Proteins / Q000378:metabolism*
D039561:Eukaryotic Initiation Factor-4E; D034741:RNA, Small Interfering; D000255:Adenosine Triphosphate; D003576:Electron Transport Complex IV; D018631:ras Proteins