The protein synthetic surge in response to mitogen triggers high glycolytic enzyme levels in human lymphocytes and occurs prior to DNA synthesis

Abstract

A simultaneous increase is found in the level of protein synthesis and the major regulatory glycolytic enzyme, phosphofructokinase (PFK), in early phytohemagglutinin exposure of human lymphocytes. The induction of DNA synthesis is demonstrated to be a much later event. This indicates that the increase of glycolysis in mitogen-stimulated cells precedes cell proliferation, but occurs simultaneously with a general increase in protein synthesis. Chemical inhibitors are used to clarify the interrelationship of protein synthesis, glycolytic enzymes levels, and DNA synthesis. Inhibition of protein synthesis with cycloheximide in the mitogen-exposed lymphocytes prevents any increase in PFK levels, implicating protein synthesis as a cause for the increased glycolysis. Cycloheximide also prevents entry into S phase in mitogen-stimulated lymphocytes which may be due to inhibition of the synthesis of enzymes necessary for DNA synthesis, such as DNA polymerase. Aphidicolin, a specific DNA polymerase inhibitor, is found to have no effect on the increase in protein synthesis and PFK levels that precedes DNA synthesis. The increase in glycolysis in mitogen-stimulated lymphocytes occurs simultaneously with, and is dependent upon, increased protein synthesis, and precedes DNA synthesis and lymphocyte proliferation; thus, the high glycolytic rate of mitogen-stimulated cells is not merely a secondary manifestation of rapid cell proliferation as has been previously reported.