[Effect of metformin on gene expression of phosphoenolpyruvate carboxykinase].
OBJECTIVE
To investigate the effect and mechanism of antihyperglycemic agent metformin on the gene expression of phosphoenolpyruvate carboxykinase (PEPCK)-a key enzyme within the regulation of gluconeogenesis in hepatocytes and to determine whether the effects of metformin on hepatocytes are transmitted throughout the known insulin signaling pathways.


METHODS
Confluent H4IIE rat heptoma cells were cultured with metformin 0.1 mmol/L for 16 h and then stimulated with various agents: insulin, cyclic adenosine monophosphate (cAMP), dexamethasone, signaling transduction inhibitor wortmannin and UO126. The gene expression of PEPCK was examined by Northern blot analysis.


RESULTS
Metformin significantly decreased basal PEPCK mRNA levels by 75% (P < 0.01). Incubation with metformin alone had no significant effect on cAMP/dexamethasone stimulated PEPCK gene expression. In contrast, insulin 0.1 nmol/L significantly inhibited cAMP/dexamethasone stimulated PEPCK gene expression by 67% (P < 0.01), when insulin 0.1 nmol/L was present together with metformin, cAMP/dexamethasone induced PEPCK gene expression was decreased by 94% (P < 0.01). Both insulin signaling pathway inhibitors, phosphatidyl-inositol-3-kinase (PI3K) inhibitor wortmannin and mitogen-activated protein kinase (MAPK) inhibitor UO126, had no significant effect on inhibited PEPCK mRNA expression by metformin, but wortmannin blocked significantly inhibitory regulation of insulin on PEPCK gene expression (P < 0.01).


CONCLUSIONS
Metformin can inhibit the PEPCK gene expression via either an insulin-independent or interaction with insulin manner. The inhibitory effects of insulin on PEPCK gene expression are mediated through PI3K pathway, not MAPK pathway.
Yuan
Li
L
Department of Endocrinology in Union Hospital of Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430022, China. yuanli18cnf@yahoo.com.cn
Ziegler
Reinhard
R
Hamann
Andreas
A
D000818:Animals; D015870:Gene Expression / Q000187:drug effects*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000502:physiology*; D008687:Metformin / Q000494:pharmacology*; D019764:Phosphoenolpyruvate Carboxykinase (ATP) / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured
D007004:Hypoglycemic Agents; D007328:Insulin; D012333:RNA, Messenger; D008687:Metformin; D019764:Phosphoenolpyruvate Carboxykinase (ATP)