Glucose regulates the promoter activity of aldolase A and pyruvate kinase M₂ via dephosphorylation of Sp1

Abstract

Proliferating cells and tumour cells maintain a high glycolytic rate even under aerobic conditions. FT02B cells, a rat hepatoma cell line, show high activities of glycolytic enzymes. Within a culture period of 48 h the cell number increases 5-fold. Replacement of glucose by pyruvate in the culture medium lowers glycolytic enzyme activity and prevents proliferation. Transfection assays revealed that glucose deprivation dramatically decreases the transcriptional activities of the Spl-dependent aldolase and pyruvate kinase promoters leading to reduced reporter gene expression. Spl binding activity is also inhibited by ocadaic acid, an inhibitor of protein phosphatase 1. Western blot analyses with nuclear extracts from FT02B cells cultured in the presence or absence of glucose revealed differences in the phosphorylation state of Spl. From these results we conclude that glucose increases the amount of the dephosphorylated form of Spl which has a higher DNA binding activity. As a consequence gene expression of the glycolytic enzymes is increased which is a prerequisite for cell proliferation.

Sp1 Transcriptional Activity Is Up-regulated by Phosphatase 2A in Dividing T Lymphocytes

“…Moreover, PP2A, but not PP1, enhanced the IL-2-driven up-regulation of Sp1 site-mediated transcriptional activity. In contrast to our data, PP1 has been implicated in glucose-induced dephosphorylation of Sp1 (39,40). The latter studies, however, did not determine whether PP1 physically interacted with Sp1, and it is conceivable that the enzyme acts upstream of a PP2A/Sp1 signaling complex.…”

“…Furthermore, increased phosphorylation either enhances (6,64) or inhibits Sp1 DNA binding and transactivation (65). Conversely, dephosphorylation can increase both activities (38,40). These discrepancies most likely illustrate the fact that Sp1 regulation has been analyzed at different stages of cell growth and differentiation and that multiple triggering signals and cell types have been used.…”

“…Conversely, decreased activity of phosphorylated Sp1 can also occur, as in the case of the casein kinase II (CKII)-mediated inhibition observed upon terminal differentiation of the liver (37, 38). It is noteworthy that the serine/threonine phosphatase I (PP1) counteracts Sp1 phosphorylation in a positive manner (39), but the phosphatase inhibitor okadaic acid has a negative effect (39,40).…”

Sp Family Members and Nuclear Factor-Y Cooperatively Stimulate Transcription from the Rat Pyruvate Kinase M Gene Distal Promoter Region via Their Direct Interactions

“…Sp1 stimulates cAMPdependent transcriptional stimulation from the CYP11A gene promoter in SL2 cells (52). However, it has been reported that the phosphorylated and the nonreduced form of Sp1 showed a decrease in binding to a DNA fragment that contained both GC boxes 1 and 2 of the PKM gene (51,53). On the other hand, cdc25C gene transcription, which occurs late in the S/G 2 phase, is regulated by a cell cycle-dependent repressor element and an upstream activating sequences which contains three CCAAT motifs and two Sp1-binding sites.…”

Sp1 Is Required for Glucose-Induced Transcriptional Regulation of Mouse Vesicular Glutamate Transporter 2 Gene

“…It has been shown that the DNA binding activity of Sp1 can be modulated either positively or negatively by phosphorylation [37][38][39] . For glucose-responsive genes, a glucose-dependent Sp1 dephosphorylation has been suggested to be responsible for glucose-mediated activation of the aldolase A gene 40 . We have found that glucose treatment increases phosphorylation of MAP kinases P38 and P44/42, and thus induces phosphorylation of the existing Sp1 protein without changing the amount of total Sp1 protein.…”