GLUCOSE-DEPENDENT REGULATION OF THE L-PYRUVATE KINASE GENE IN A HEPATOMA-CELL LINE IS INDEPENDENT OF INSULIN AND CYCLIC-AMP

Hepatocyte-like mhAT3F cells have been derived from the hepatoma of a transgenic mouse expressing the SV40 large T antigen under the control of the antithrombin III gene regulatory region (Antoine, B., Levrat, F., Vallet, V., Berbar, T., Cartier, N., Dubois, N., Briand, P., and K ahn, A. (1992) Gene expression in hepatocyte-like lines established by targeted carcinogenesis in transgenic mice. Exp. Cell. Res. 200, 175- 185; F. Levrat et al., unpublished results). In these cells, the L-PK gene is transcriptionally activated by glucose, as it is in vivo and i n cultured hepatocytes. However, in contrast to the L-PK gene regulati on in the liver and isolated hepatocytes, the glucose responsiveness d oes not require insulin and is not blocked by cyclic AMP. In mhAT3F ce lls, the insensitivity to insulin might be due to the replacement of i nsulin-dependent glucokinase by insulin-independent hexokinases able t o phosphorylate glucose in the absence of the hormone. The glucose-dep endent activation of the L-PK gene is delayed, requires ongoing protei n synthesis, and is mediated by the same glucose response element as i n vivo and in isolated hepatocytes. These results suggest that the glu cose-dependent signaling pathway responsible for the transcriptional a ctivation of glycolytic and lipogenic genes requires glucose phosphory lation, a phenomenon that is insulin-dependent in the liver but insuli n-independent in cultured hepatoma cells. Nevertheless, the action of glucose 6-phosphate is most likely indirect.