Enhancing Mitochondrial Respiration Suppresses Tumor Promoter TPA-Induced PKM2 Expression and Cell Transformation in Skin Epidermal JB6 Cells

Abstract

Differentiated cells primarily metabolize glucose for energy via the tricarboxylic acid cycle and oxidative phosphorylation, but cancer cells thrive on a different mechanism to produce energy, characterized as the Warburg effect, which describes the increased dependence on aerobic glycolysis. The M2 isoform of pyruvate kinase (PKM2), which is responsible for catalyzing the final step of aerobic glycolysis, is highly expressed in cancer cells and may contribute to the Warburg effect. However, whether PKM2 plays a contributing role during early cancer development is unclear. In our studies, we have made an attempt to elucidate the effects of varying mitochondrial respiration substrates on skin cell transformation and expression of PKM2. Tumorigenicity in murine skin epidermal JB6 P+ (promotable) cells was measured in a soft agar assay using 12-O-tetradecanoylphorbol-13-acetate (TPA) as a tumor promoter. We observed a significant reduction in cell transformation upon pretreatment with the mitochondrial respiration substrate succinate or malate/pyruvate. We observed that increased expression and activity of PKM2 in TPA-treated JB6 P+ cells and pretreatment with succinate or malate/pyruvate suppressed the effects. In addition, TPA treatment also induced PKM2 whereas PKM1 expression was suppressed in mouse skin epidermal tissues in vivo. In comparison with JB6 P+ cells, the nonpromotable JB6 P− cells showed no increase in PKM2 expression or activity upon TPA treatment. Knockdown of PKM2 using a siRNA approach significantly reduced skin cell transformation. Thus, our results suggest that PKM2 activation could be an early event and play a contributing role in skin tumorigenesis.

Pyruvate Kinase M2: Multiple Faces for Conferring Benefits on Cancer Cells

“…PKM2 expression was shown to be involved in early tumorigenesis (28) and can be detected in the blood and stool of cancer patients (9,82); furthermore, increases in PKM2 levels were reported to correlate with tumor size and stage (9). As described in another article in this CCR Focus section by Yang and colleagues, mutations of IDH1 and IDH2 are also reported to be easily detectable using small amounts of tumor samples (83).…”

“…12-O-tetradecanoylphorbol-13-acetate, PKM2 expression might be an early event in carcinogenesis (28). Thus, PKM2 can be a useful biomarker for the early detection of tumors.…”

“…A variety of molecules interact with PKM2 (5,6,8,14,18,19,21,23,24,28,(36)(37)(38)(39)(40)(41)(42)(43)(44)(45)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60)(61)(62)(63)(64)(65). Many of them affect the glycolytic functions of PKM2, which directly regulate the Warburg effect.…”

Manganese Superoxide Dismutase in Cancer Prevention

“…It was demonstrated that deficiencies in mitochondrial respiration lead to reduced nicotinamide adenine dinucleotide (NADH) accumulation resulting in inactivation of PTEN and activation of the Akt survival pathway. Our previous studies have revealed that tumor promoters can decrease mitochondrial respiration which coincides with early metabolic changes as a mechanism to promote carcinogenesis (111,146,150). Although decreased mitochondrial respiration has been shown in various cancer cell lines, this is not true for all cancer cells.…”

“…4). To provide evidence that alterations in mitochondrial respiration have a direct impact on the glycolytic phenotype, PKM2 protein expression and activity in skin epidermal JB6 P + cells following mitochondrial respiration substrate pretreatment were measured and the results showed that PKM2 expression was significantly decreased (150). Although the expression of pyruvate kinase M1 isoform (PKM1) occurs in normal adult cells, tumor cells express the PKM2 isoform which has been reported as an alternative splice variant of the M1 isoform.…”