Abstract 2914: A role for glycolysis in the c-Met/HGF signaling axis

Abstract

Mitochondrial respiration is the most efficient form of energy production in the cell; however, in the absence of oxygen, such as within a solid tumor mass, cells rely on glycolysis as the main source of energy. Under hypoxic conditions the end product of glycolysis, pyruvate, is reduced to lactate by lactate dehydrogenase (LDH), which is then exported out of the cell. This reduction is essential to regenerate NAD+ consumed by the earlier steps of glycolysis. Recent evidence suggests that hepatocyte growth factor (HGF), the only known ligand for the c-Met receptor, causes an increase in glycolysis. This led our laboratory to hypothesize that glycolysis may be required for HGF-induced phenotypic changes in cancer cells. HGF signaling through the c-Met receptor induces an epithelial-mesenchymal transition (EMT), including loss of cell-cell adhesions through down-regulation of E-cadherin expression, as well as increased motility and cell scattering characteristic of the initiating steps leading to cancer cell invasion and metastasis. Using DU145 prostate cancer cells, we have found that inhibitors of glycolysis (2-DG) and lactate production via LDH activity (oxamate), were able to inhibit HGF-induced cell scattering. Using a wound healing assay, we observed that oxamate was able to prevent HGF-induced cell migration, suggesting a role for glycolysis in cell motility. Additionally, lactic acid was able to rescue cell scattering and wound healing blocked by oxamate, but not by 2-DG. Lactic acid measurements showed that oxamate prevented an increase in glycolysis stimulated by HGF. Measurement of ATP levels also suggested that 2-DG was able to block cell motility due to a reduction in ATP, while oxamate appeared to work through a yet undetermined method. Western blot analysis indicated that oxamate caused a decrease in HGF-induced phospho-Met and downstream phospho-Akt levels. Using H1993 lung cancer cells with constitutively active c-Met, we were able to determine that oxamate deactivated c-Met, while not affecting total c-Met levels. The ability of oxamate to reduce phosphorylation levels appeared to be Met specific based on its inability to block phosphorylation of other activated receptors. Oxamate not only inhibits LDH, but also aspartate aminotransferase (AAT), an enzyme involved in the malate-aspartate shuttle. Our data suggest, however, that the ability of oxamate to inhibit HGF-induced signaling and cell scattering is not through its ability to inhibit AAT. Taken together, our data suggest the c-Met/HGF signaling axis is dependent on glycolysis and perhaps lactic acid levels. Our long-term goals are to elucidate the specific mechanism for this dependence as a means of defining novel targets for preventing c-Met-mediated cancer cell invasion and metastasis. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2914. doi:10.1158/1538-7445.AM2011-2914

HGF/Met Signaling in Head and Neck Cancer: Impact on the Tumor Microenvironment

“…There is evidence that HGF/Met signaling results in higher lactate secretion by cancer cells via upregulation of glycolysis (65). Lactate was shown to potently suppress the proliferation and activity of human CTLs (66).…”