Differences in oxygen-dependent regulation of enzymes between tumor and normal cell systems in culture

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Abstract
Metabolic studies in tumor cells have indicated that bioenergetic regulatory mechanisms geared to acute changes in oxygen availability are abnormal. In the present studies we have examined bioenergetic adaptations to chronic oxygen depletion in culture maintained tumor cells in comparison to normal cell lines. Activities of two key glycolytic enzymes (pyruvate kinase (PyKi) and phosphofructokinase (PFK)) were measured in two tumor cell lines (fibrosarcoma (FS) and Hela) and two normal cell lines (rat lung fibroblasts (RLF) and WI‐38) maintained in culture for up to 96 hours under aerobic (PO2 ∼ 140) and hypoxic PO2 ∼ (15) conditions. Exposure to low O2 tensions for 96 hours resulted in significant increases in PyKi and PFK in both RLF and WI‐38, but did not alter activities of these enzymes in either FS or HeLa cell systems. Activities of two enzymes involved in O2 metabolism (cytochrome oxidase (CyOx)) and superoxide dismutase (SOD) were also measured in the two tumor cell lines and in RLF. Chronic hypoxia significantly decreased the activities of CyOx and SOD in RLF cell systems but did not alter the activities of these enzymes in the tumor cells. In these studies, the tumor‐derived cell lines do not demonstrate specific enzymatic responses to sustained oxygen depletion in vitro noted in normal cell systems, suggesting significant abnormalities in regulatory mechanisms geared to chronic changes in molecular O2.