FIGURE 1.

Polyamines and myc. A, polyamine metabolism. Synthesis reactions are depicted with dark gray arrows, whereas degradation reactions are represented with pale gray arrows. Reactions inside the circle take place in mitochondria. B, Myc oncoprotein is a common transcription factor controlling PA metabolism and glycolysis. Myc transactivates several PA synthetic genes and glycolytic enzymes and also the translation initiation factor eIF5A2, which has a unique posttranslational modification dependent on spermidine (2); in turn, spermidine stimulates myc transcription (3). ADC, arginine decarboxylase (controversial (4)); APAO, acetylpolyamine oxidase; MAT, methionine adenosyltransferase; SMO, spermine oxidase; SpmS, spermine synthase; SpdS, spermidine synthase.