Up-regulation of fibroblast growth factor-binding protein, by beta-catenin during colon carcinogenesis.

Fibroblast growth factor-binding protein (FGF-BP) releases immobilized FGFs from the extracellular matrix and can function as an angiogenic switch molecule in cancer. Here we show that FGF-BP is up-regulated in early dysplastic lesions of the human colon that are typically associated with a loss of adenomatous polyposis coli and up-regulation of beta-catenin. In addition, FGF-BP expression is induced in dysplastic lesions in ApcMin/+ mice in parallel with the up-regulation of beta-catenin.

Erk activation is required for Nrf2 nuclear localization during pyrrolidine dithiocarbamate induction of glutamate cysteine ligase modulatory gene expression in HepG2 cells.

Pyrrolidine dithiocarbamate (PDTC) induction of the human glutamate cysteine ligase modulatory (GCLM) gene is dependent on activation of the mitogen-activated protein kinases (MAPKs) extracellular regulated kinase (Erk) and p38, and is not affected by protein kinase C (PKC) or PI3K inhibitors. Nrf2 binding to the electrophile response element (EpRE) located within the GCLM promoter is decreased after MAPK inhibition, suggesting that Nrf2 could be a downstream target of activated MAPK. To evaluate this hypothesis, a series of Nrf2 proteins harboring mutations in conserved consensus MAPK phosphorylation sites were developed and used in multiple functional assays.

The Keap1 BTB/POZ dimerization function is required to sequester Nrf2 in cytoplasm.

Transactivation of phase II detoxification enzymes and antioxidant proteins is mediated by the Cap'N'Collar transcription factor, Nrf2, which is sequestered in the cytoplasm by the actin-binding protein Keap1. Mutation of a conserved serine (S104A) within the Keap1 BTB/POZ domain disrupts Keap1 dimerization and eliminates the ability of Keap1 to sequester Nrf2 in the cytoplasm and repress Nrf2 transactivation. Disruption of endogenous Keap1 dimerization using BTB/POZ dominant negative proteins also inhibits the ability of Keap1 to retain Nrf2 in the cytoplasm.