The glucose-responsive transcription factor carbohydrate responsive element binding protein (ChREBP) plays an important role in regulating glucose metabolism in support of anabolic synthesis in both hepatocytes and cancer cells. In order to further investigate the molecular mechanism by which ChREBP regulates transcription, we used a proteomic approach to identify proteins interacting with ChREBP. We found several potential ChREBP-interacting partners, one of which, flightless I homolog (FLII) was verified to interact and co-localize with ChREBP in HCT116 colorectal cancer and HepG2 hepatocellular carcinoma cells. FLII is a member of the gelsolin superfamily of actin-remodeling proteins and can function as a transcriptional co-regulator. The C-terminal 227 amino acid region of ChREBP containing the DNA-binding domain interacted with FLII. Both the N-terminal leucine-rich repeat (LRR) domain and C-terminal gelsolin homolog domain (GLD) of FLII interacted and co-localized with ChREBP. ChREBP and FLII localized in both the cytoplasm and nucleus of cancer cells. Glucose increased expression and nuclear localization of ChREBP, and had minimal effect on the level and distribution of FLII. FLII knockdown using siRNAs increased mRNA and protein levels of ChREBP-activated genes and decreased transcription of ChREBP-repressed genes in cancer cells. Conversely, FLII overexpression negatively regulated ChREBP-mediated transcription in cancer cells. Our findings suggest that FLII is a component of the ChREBP transcriptional complex and negatively regulates ChREBP function in cancer cells.
Keywords: ACC; Cancer; ChREBP; ChoRE; FAS; FGF21; FLAP1; FLII; FLII leucine rich repeat associated protein 1; G6Pase; GLD; Glucose; HATs; HDACs; LPK; LRR; NES; NLS; PEPCK; Pro-rich; Proline-rich domain; RNA interference; RNAi; SCD1; TXNIP; Transcriptional activity; ZIP-like; acetyl-CoA carboxylase; b/HLH/ZIP; bHLH-LZ; basic helix–loop–helix leucine zipper; basic helix–loop–helix leucine zipper domain; carbohydrate response element; carbohydrate responsive element binding protein; fatty acid synthase; fibroblast growth factor 21; flightless I homolog; gelsolin-like domain; glucose-6-phosphatase catalytic subunit; histone acetyltransferases; histone deacetylases; leucine-rich repeat; leucine-zipper-like domain; liver pyruvate kinase; nuclear export signal; nuclear localization signal; phosphoenolpyruvate carboxykinase; stearoyl-CoA desaturase-1; thioredoxin-interacting protein.
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