Mitochondrial Respiration Promotes Non-Small Cell Lung Cancer Cell Proliferation and Function
Lung cancer is the leading cause of cancer related death both in the USA and worldwide. More than 80% of the lung cancer cases are non-small cell lung cancer (NSCLC). Since Otto Warburg made the first observation that the rate of aerobic glycolisis is increased in tumor cells, substantial amount of research has been done on altered cancer cell metabolism and bioenergetics. Recently, the use of more advanced metabolomics and genomics technologies has revealed the remarkable plasticity of tumor metabolism and bioenergetics. Many types of tumor cells have been shown to generate most of the cellular energy via mitochondrial respiration and oxidative phosphorylation. In this dissertation project it has been shown that the rate of respiration is intensified in an array of NSCLCs compared to the normal lung cell line. We also found that the respiration is greatly reduced when NSCLCs are grown in glutamine deprived media, whereas the respiration is unaffected when the cells are grown in glucose deprived media. In this project we have also shown that Hedgehog (Hh) signaling inhibitors Cyclopamine tartrate (CycT) and SNAT1 disrupt mitochondrial function and aerobic respiration. Our results showed that CycT, like glutamine depletion, caused a substantial decrease in oxygen consumption in a number of NSCLC cell lines, suppressed NSCLC cell proliferation, and induced apoptosis. Further, we found that CycT increased reactive oxygen species (ROS) generation, causes mitochondrial membrane hyperpolarization, and mitochondrial fragmentation, thereby disrupting mitochondrial function in NSCLC cells. Furthermore, using two isogenic cell lines representing matched pairs of normal and cancer cells, we have identified changes in protein levels accompanying transformation of normal lung epithelial cells to cancer cells. Surprisingly, a substantial number of proteins involved in actin cytoskeleton were preferentially downregualted in cancer cells. However, similar numbers of proteins in other organelles were either up or down regulated. The formation of stress fibers and focal adhesions were also markedly decreased in cancer cells. Protein network analysis showed that the altered proteins are highly connected.