Williams-Beuren syndrome (WBS) (MIM.194050) is a multisystem developmental disorder caused by the deletion of contiguous genes at chromosome 7q11.23. A common interval that includes as many as 17 genes is deleted in most patients. CHREBP (WBSCR14) is included in this region
WBSCR14 encodes a protein belonging to the basic helix-loop-helix (HLHs) leucine-zipper (LZs) family of transcription factors (TFs).
Function
Although insulin and glucagon play important roles in regulating the response of cells to nutrients, cells also respond to carbohydrates through transcriptional regulation by the glucose responsive transcription factor ChREBP (WBSCR14).
ChREBP, carbohydrate responsive element binding protein, is a transcription factor that is activated by high levels of carbohydrates and repressed by cAMP.
The activation of ChREBP by elevated carbohydrate levels increases the activity of genes involved in glucose metabolism such as pyruvate kinase, a rate-limiting enzyme in glycolysis, increasing the overall rate of utilization of carbohydrates.
Excess carbohydrates also increase the transcription of genes that convert carbohydrates to triglycerides in the liver for storage in adipose tissue. cAMP regulates ChREBP activity by activating PKA, which phosphorylates ChREBP.
Phosphorylation of ChREBP at ser(196) inactivates nuclear import and phosphorylation at Thr(666) prevents DNA binding by ChREBP.
A metabolite of glucose activates protein phosphatase PP2A that then dephosphorylates both sites on ChREBP in response to increased glucose levels and increases ChREBP activity. Other pathways also regulate ChREBP activity and response to nutrients.
High fat diets repress ChREBP activation by increasing AMP in liver cells, activating the AMP kinase.
Phosphorylation of ChREBP by AMP kinase inactivates ChREBP and blocks glucose induction of ChREBP, linking dietary fatty acids to the regulation of carbohydrate metabolism. (Biocarta)
References
Cairo, S.; Merla, G.; Urbinati, F.; Ballabio, A.; Reymond, A. : WBSCR14, a gene mapping to the Williams-Beuren syndrome deleted region, is a new member of the Mlx transcription factor network. Hum. Molec. Genet. 10: 617-627, 2001. PubMed ID : 11230181
de Luis, O.; Valero, M. C.; Perez Jurado, L. A. : WBSCR14, a putative transcription factor gene deleted in Williams-Beuren syndrome: complete characterisation of the human gene and the mouse ortholog. Europ. J. Hum. Genet. 8: 215-222, 2000. PubMed ID : 10780788