The online version of this article (doi:10.1186/1476-4598-11-60) contains supplementary material, which is available to authorized users.
The authors declare that they have no competing interests.
ST conducted the K-ras and COX Vb siRNA experiments, soft agar and in vivo experiments and participated in the conception of the manuscript. KKN assisted with the COX assay. DLS conducted the EIF4E siRNA experiments. AY assisted in the in vivo experiments. JMT assisted in the development of the COX assay. YI assisted in the in vivo experiments. ACK conducted the real time RT-PCR. HF conducted the histopathological review of the tumors. BFC assisted with the oxygen consumption experiments. JWE participated in the design of the experiments and interpretation of the data. JC conceived the research, directed all experiments and drafted the manuscript. All the authors have been involved in the drafting of the manuscript and have read and approved the final manuscript.
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).
We found that the introduction of activated H-RasV12 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.
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.
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- Cytochrome c oxidase is activated by the oncoprotein Ras and is required for A549 lung adenocarcinoma growth
Kristin K Nelson
Deanna L Siow
Joshua M Thornburg
Alden C Klarer
Brian F Clem
John W Eaton
- BioMed Central
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