The major goal of this project is to determine whether targeting pyruvate kinase M2 (PKM2), the enzyme in the last step of glycolysis, can serve as a novel chemopreventive approach. Upregulation of PKM2 has been reported in many types of human cancers;however, whether PKM2 is activated during the early stage of tumorigenesis and therefore, whether inhibiting PKM2 activation can serve as a chemopreventive approach are unclear. It was first discovered in the 1920's by Otto Warburg and co-workers that cancer cells, in the presence of oxygen, utilize high rates of glycolysis followed by lactic acid fermentation to produce energy. This biological process was coined the "Warburg Effect." Cancer cells adapt to aerobic glycolysis by up/down regulating key metabolic enzymes including pyruvate kinase, the enzyme that converts phosphoeno pyruvate to pyruvate. Cancer cells overexpress the M2 isoform (PKM2) while reduce the expression of the M1 isoform of pyruvate kinase. However, at which stage during tumorigenesis PKM2 activation is initiated and the underlying mechanism of activation remain unclear. Furthermore, it is unknown whether PKM2 activation is regulated by the intracellular redox status and what role oxidative stress may play in leading to the activation of PKM2 in human cancers. Using the multistage skin carcinogenesis mouse model, our initial studies have shown that PKM2 expression and activity are increased during the early stages of tumor formation;and downregulation of PKM2 can suppress neoplastic transformation of mouse skin epidermal cells. We utilized two clonal variants of the JB6 mouse skin epidermal cell line, promotable JB6 (P+) and non-promotable (P-) cells with varying levels of manganese superoxide dismutase (MnSOD) expression, to determine a relationship between oxidative stress and PKM2 activation. We found that (P+) cells with lower levels of MnSOD and higher levels of oxidative stress, compared to their P- counterparts, showed higher levels of PKM2 expression and activity following tumor promoter treatment. By applying the two-stage skin carcinogenesis paradigm to MnSOD non-transgenic and transgenic mice, we found that overexpression of MnSOD suppressed carcinogen-induced PKM2 activation, suggesting that intracellular redox status can modulate PKM2 activation during tumorigenesis. Based on these studies, we hypothesize that PKM2 activation is a tumor promoting event during early cancer development and oxidative stress is conducive to PKM2 activation.
The aims of this application are as follows:
Specific Aim 1 : Can inhibition of PKM2 activity suppress carcinogenesis? Specific Aim 2: Does oxidative stress contribute to PKM2 activation? We expect this application will show a high impact: the role of PKM2 in early cancer development will be defined;the underlying mechanisms can be utilized as potential drug targets for cancer prevention.
The activation of pyruvate kinase M2 (PKM2) has been observed in our early tumorigenesis models and inhibition of PKM2 activation suppresses cell transformation, suggesting that the metabolic shift may occur at the very early stage of cancer development. This application will study whether inhibition of PKM2 may serve as a novel chemopreventive approach and whether oxidative stress activates PKM2. 1
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