ZBTB34, a novel human BTB/POZ zinc finger protein, is a potential transcriptional repressor

Our work has identified a cancer-specific, cell surface and growth-related quinol oxidase with both NADH oxidase and protein disulfide-thiol interchange activities, a member of the ECTO-NOX protein family designated tNOX. We provide evidence for tNOX as an alternative drug target to COX-2 to explain the anticancer activity of COX inhibitors. Non-steroidal anti-inflammatory drugs (NSAIDS), piroxicam, aspirin, ibuprofen, naproxen and celecoxib all specifically inhibited tNOX activity of HeLa (human cervical carcinoma) and BT-20 (human mammary carcinoma) cells (IC₅₀ in the nanomolar range) without effect on ECTO-NOX activities of non-cancer MCF-10A mammary epithelial cells. With cancer cells, rofecoxib was less effective and two NSAIDS selective for COX-1 were without effect in inhibiting NOX activity. The IC₅₀ for inhibition of tNOX activity of HeLa cells and the IC₅₀ for inhibition of growth of HeLa cells in culture were closely correlated. The findings provide evidence for a new drug target to account for anticancer effects of NSAIDS that occur independent of COX-2.     

The yeast putative transcriptional repressor RGM1 is a proline-rich zinc finger protein

I have cloned a yeast gene, RGM1, which encodes a proline-rich zinc, finger protein. rgm1 mutants do not show any obvious phenotype but overexpression of RGM1 gene greatly impairs cell growth. The proline-rich region of RGM1 attached to a heterologous DNA binding domain is able to repress the expression of the target gene. RGM1 shares similar zinc finger motifs with the mammalian Egr (early growth response) proteins as well as proline-rich sequences with a high serine and threonine content, suggesting that RGM1 and Egr proteins could have functional similarities.     

Structure of the Wilms tumor suppressor protein zinc finger domain bound to DNA

The zinc finger domain of the Wilms tumor suppressor protein (WT1) contains four canonical Cys(2)His(2) zinc fingers. WT1 binds preferentially to DNA sequences that are closely related to the EGR-1 consensus site. We report the structure determination by both X-ray crystallography and NMR spectroscopy of the WT1 zinc finger domain in complex with DNA. The X-ray structure was determined for the complex with a cognate 14 base-pair oligonucleotide, and composite X-ray/NMR structures were determined for complexes with both the 14 base-pair and an extended 17 base-pair DNA. This combined approach allowed unambiguous determination of the position of the first zinc finger, which is influenced by lattice contacts in the crystal structure. The crystal structure shows the second, third and fourth zinc finger domains inserted deep into the major groove of the DNA where they make base-specific interactions. The DNA duplex is distorted in the vicinity of the first zinc finger, with a cytidine twisted and tilted out of the base stack to pack against finger 1 and the tip of finger 2. By contrast, the composite X-ray/NMR structures show that finger 1 continues to follow the major groove in the solution complexes. However, the orientation of the helix is non-canonical, and the fingertip and the N terminus of the helix project out of the major groove; as a consequence, the zinc finger side-chains that are commonly involved in base recognition make no contact with the DNA. We conclude that finger 1 helps to anchor WT1 to the DNA by amplifying the binding affinity although it does not contribute significantly to binding specificity. The structures provide molecular level insights into the potential consequences of mutations in zinc fingers 2 and 3 that are associated with Denys-Drash syndrome and nephritic syndrome. The mutations are of two types, and either destabilize the zinc finger structure or replace key base contact residues.