Expression of two type II-like tumor hexokinase RNA transcripts in cancer cell lines.

To maintain an elevated glycolytic rate, cancerous or proliferating cells alter the expression pattern of rate limiting glycolytic enzymes. Since glucose phosphorylation is the first step in glycolysis, hexokinase (HK), the first rate limiting glycolytic enzyme, can play a key regulatory role in this process. A low-Km, mitochondrial type II-like tumor HK is described as the predominant form in hepatomas. However, recent identification of a high-Km glucose phosphorylating activity in a range of cancer cells prompted us to characterize glucose phosphorylating enzymes of cancer cells at the molecular level. Highly sensitive reverse-transcription polymerase chain reaction identifies an induction and overexpression of a type II-like tumor HK RNA in a range of cancer cell lines irrespective of tissue origin. In addition, we report here the identification of two RNA transcripts of type II-like tumor HK of approximately 5.5 and approximately 4.0 kb in these cancer cells lines, including muscle-derived L6 myoblast cells. Interestingly, under normal conditions muscle cells express only a approximately 5.5-kb type II HK RNA transcript. A significant amount of type I HK RNA was also found expressed in cancer cell lines. RNA encoding glucokinase (GK), the high-Km HK isozyme, was found only in cancer cells originating from liver and pancreas, which express GK under normal conditions.