Double role of pyruvate kinase type M2 in the regulation of phosphometabolite pools

Abstract

Proliferating nonnal cells and tumor cells typically express a particular isoenzyme of pyruvate kinase called type M 2-PK. This isoenzyme exists in two different forms: the so-called tumor M 2-PK, which is strongly overexpressed in tumor cells, and the lung M 2-PK, which is the predominant species found in lung. The tumor M 2-PK mainly appears in a trimeric or dimeric state and has a low affinity for its substrate phosphoenolpyruvate. The lung M 2-PK is always tetrameric and has a high affinity for phophoenolpyruvate. Using a temperature-sensitive mutant of pp60v-src kinase, we have investigated the influence of transfonnation on the amount of the two fonns of pyruvate kinase type M2 in different host cells. The appearance of the tumor M 2-PK is detectable 3 h and is maximal 12 h after onset of transfonnation and follows the activation of the pp60v-src tyrosine kinase. The tumor M 2-PK has a high level of specific phosphorylation in serine and tyrosine, whereas in lung M 2-PK phosphorylation can hardly be detected. From this and from in vitro phosphorylation experiments, we conclude that the phosphorylation of the tetrameric lung type of M 2-PK leads to a breakdown to the dimeric tumor M 2-PK. The appearance of the low PEP-affinity fonn of pyruvate kinase within 3 h after transfonnation correlates with an increase of the glycolytic phosphometabolite pools and of the synthetic products derived from them, e.g., P-ribose-PP. Some of these phosphometabolites, e.g., AMP and NADH, represent links between metabolism and cell proliferation.