Variations of fructose-2,6-diphosphate levels in cultured HT29 human colon cancer cells: influence of hexoses and lactate concentrations.

Under the standard conditions of culture, Fru-2,6-P2 level in HT29 cells is transitorily increased as a consequence of medium change; the peak value occurs after 2 hr, followed by a gradual return to a basal value (40 pmol/mg protein) which is maintained as long as medium glucose concentration stands above 2 mM. A 20 hr glucose deprivation lowers Fru-2,6-P2 level to trace value, but, when glucose is reintroduced, the peak value is much higher; large Fru-2,6-P2 accumulation is correlated with higher rates of glucose uptake and lactate release, which suggests an activation of glycolysis at the level of phosphofructokinase-1. Fru-2,6-P2 level depends on the glucose concentration within the range of 0 to 5 mM. At this concentration and above, maximal effect is reached. Previous glucose deprivation renders the Fru-2,6-P2 forming system more sensitive to glucose. When given instead of glucose, fructose enters the glycolytic pathway and produces same effect as glucose on the Fru-2,6-P2 level. Galactose turns it to almost zero which coincides with low glycolytic rate. Acidity of the culture medium favorishes the Fru-2,6-P2 formation; however, change in pH cannot explain the variations of Fru-2,6-P2 level observed under the standard culture conditions. Lactate concentrations over 10 mM in the medium are found to significantly inhibit the Fru-2,6-P2 producing system. Therefore, lactate accumulation in the medium could be an important factor controlling Fru-2,6-P2 level during standard cell culture.