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cancer metabolism, pyruvate kinase, proteomics, amino acid profile
Abstract:
The glycolytic enzyme pyruvate kinase (PK) is required for cancer development,
and has been implicated in the metabolic transition from oxidative to fermentative
metabolism, the Warburg effect. However, the global metabolic response that follows
changes in PK activity is not yet fully understood. Using shotgun proteomics, we
identified 31 yeast proteins that were regulated in a PK-dependent manner. Selective
reaction monitoring confirmed that their expression was dependent on PK isoform,
level and activity. Most of the PK targets were amino acid metabolizing enzymes
or factors of protein translation, indicating that PK plays a global regulatory role in
biosynthethic amino acid metabolism. Indeed, we found strongly altered amino acid
profiles when PK levels were changed. Low PK levels increased the cellular glutamine
and glutamate concentrations, but decreased the levels of seven amino acids including
serine and histidine. To test for evolutionary conservation of this PK function, we
quantified orthologues of the identified PK targets in thyroid follicular adenoma, a
tumor characterized by high PK levels and low respiratory activity. Aminopeptidase
AAP-1 and serine hydroxymethyltransferase SHMT1 both showed PKM2- concentration
dependence, and were upregulated in the tumor. Thus, PK expression levels and
activity were important for maintaining cellular amino acid homeostasis. Mediating
between energy production, ROS clearance and amino acid biosynthesis, PK thus plays
a central regulatory role in the metabolism of proliferating cells.
