Expression, purification, and characterization of the 4 zinc finger region of human tumor suppressor WT1

Functional Disruption of Gli1-DNA Recognition via a Cobalt(III) Complex

The aberrant activation of the Gli family of zinc finger transcription factors (ZFTFs) is associated with several types of human cancer, including medulloblastoma and basal cell carcinoma. We have reported the use of cobalt(III) Schiff-base complexes (Co(III)-sb) as potent inhibitors of ZFTFs in vivo. These complexes inhibit transcription by displacing the zinc finger domain's structural Zn(II) ion, destabilizing the alpha helix necessary for DNA recognition. Here, we describe the use of Co(III)-sb complexes for the selective inhibition of Gli1. Spectroscopic and computational studies of the Gli1 DNA binding domain found that Co(III)-sb displaced Zn(II) through direct coordination with the His residues of the Cys2 His2 Zn(II) binding site. As a result, there is a dose-dependent degradation of the alpha-helix content in the DNA binding domain of Gli1 and corresponding inhibition of consensus sequence recognition. We conclude that this strategy is well suited for the development of new and potent inhibitors of Gli1.

Multi-metal tolerance of DHHC palmitoyl transferase-like protein isolated from metal contaminated soil

The microbiota inhabiting in metal polluted environment develops strong defense mechanisms to combat pollution and sustain life. Investigating the functional genes of the eukaryotic microbiota inhabiting in these environments by using metatranscriptomics approach was the focus of this study. Size fractionated eukaryotic cDNA libraries (library A, < 0.5 kb, library B, 0.5-1.0 kb, and library C, > 1.0 kb) were constructed from RNA isolated from the metal contaminated soil. The library C was screened for Cadmium (Cd) tolerant genes by using Cd sensitive yeast mutant ycf1^Δ by functional complementation assay, which yielded various clones capable of growing in Cd amended media. One of the Cd tolerant clones, PLCg39 was selected because of its ability to grow at high concentrations of Cd. Sequence analysis of PLCg39 showed homology with DHHC palmitoyl transferases, which are responsible for addition of palmitoyl groups to proteins and usually possess metal coordination domains. The cDNA PLCg39 was able to confer tolerance to Cd-sensitive (ycf1^Δ), Copper-sensitive (cup1^Δ) and Zn-sensitive (zrc1^Δ) yeast mutants when grown at different concentrations of Cd (40-100 μM), Cu (150-1000 μM) and Zn (10-13 mM), respectively. The DHHC mutant akr1^Δ transformed with PLCg39 rescued from the metal sensitivity indicating the role of DHHC palmitoyl transferase in metal tolerance. This study demonstrated that PLCg39 acts as a potential metal tolerant gene which could be used in bioremediation, biosensing and other biotechnological fields.

Targeting of the WT191-138 fragment to human dendritic cells improves leukemia-specific T-cell responses providing an alternative approach to WT1-based vaccination

Due to its immunogenicity and overexpression concomitant with leukemia progression, Wilms tumor protein 1 (WT1) is of particular interest for immunotherapy of AML relapse after allogeneic hematopoietic stem cell transplantation (allo-HSCT). So far, WT1-specific T-cell responses have mainly been induced by vaccination with peptides presented by certain HLA alleles. However, this approach is still not widely applicable in clinical practice due to common limitations of HLA restriction. Dendritic cell (DC) vaccines electroporated with mRNA encoding full-length protein have also been tested for generating WT1-derived peptides for presentation to T-cells. Alternatively, an efficient and broad WT1 peptide presentation could be elicited by triggering receptor-mediated protein endocytosis of DCs. Therefore, we developed antibody fusion proteins consisting of an antibody specific for the DEC205 endocytic receptor on human DCs and various fragments of WT1 as DC-targeting recombinant WT1 vaccines (anti-hDEC205-WT1). Of all anti-hDEC205-WT1 fusion proteins designed for overcoming insufficient expression, anti-hDEC205-WT110-35, anti-hDEC205-WT191-138, anti-hDEC205-WT1223-273, and anti-hDEC205-WT1324-371 were identified in good yields. The anti-hDEC205-WT191-138 was capable of directly inducing ex vivo T-cell responses by co-incubation of the fusion protein-loaded monocyte-derived mature DCs and autologous T-cells of either healthy or HSCT individuals. Furthermore, the DC-targeted WT191-138-induced specific T-cells showed a strong cytotoxic activity by lysing WT1-overexpressing THP-1 leukemia cells in vitro while sparing WT1-negative hematopoietic cells. In conclusion, our approach identifies four WT1 peptide-antibody fusion proteins with sufficient production and introduces an alternative vaccine that could be easily translated into clinical practice to improve WT1-directed antileukemia immune responses after allo-HSCT.

Mechanisms of leukemia resistance to antibody dependent cellular cytotoxicity

Specific immunotherapy for acute leukemia remains a great unmet need. Native unmodified monoclonal antibody therapies, while promising, are inadequately effective for these malignancies, and multiple mechanisms for failure have been described. Antibody-dependent cellular cytotoxicity or phagocytosis is the primary modality of mAb-mediated cell killing in vivo, but ultimately leads to relapse of the leukemias, in model systems and in humans. By use of a T-cell receptor mimic mAb ESKM, derived against a WT1 peptide expressed in complex with HLA-A*02:01, whose only mechanism of therapeutic action is ADCC, we evaluated the mechanisms of leukemic relapse from its potent therapeutic action in mouse xenograft models of human leukemia. Leukemia escape was not associated with loss of the antigenic target, downregulation of cell surface HLA, antibody pharmacokinetic or biodistribution issues, or development of leukemia cell-intrinsic resistance to ADCC. Interestingly, the rapidity of leukemic growth determined whether leukemia was able to evade cytotoxicity independent of the presence of sufficient effector cells. By engineering leukemia cells with upregulated p27^Kip1 and slower cell cycling times, we show that relapse was inversely correlated with growth rates resulting in the eventual inadequacy of effector to target ratio. Moreover, lack of migration of effector cells into lymphomatous pockets of ALL also allowed local escape. Successful leukemia therapy with mAb might therefore be improved in similar situations by combination with measures to reduce burden and slow leukemia cell growth.

A TCR-mimic antibody to WT1 bypasses tyrosine kinase inhibitor resistance in human BCR-ABL+ leukemias

Acute and chronic leukemias, including CD34(+) CML cells, demonstrate increased expression of the Wilms tumor gene 1 product (WT1), making WT1 an attractive therapeutic target. However, WT1 is a currently undruggable, intracellular protein. ESKM is a human IgG1 T-cell receptor mimic monoclonal antibody directed to a 9-amino acid sequence of WT1 in the context of cell surface HLA-A*02. ESKM was therapeutically effective, alone and in combination with tyrosine kinase inhibitors (TKIs), against Philadelphia chromosome-positive acute leukemia in murine models, including a leukemia with the most common, pan-TKI, gatekeeper resistance mutation, T315I. ESKM was superior to the first-generation TKI, imatinib. Combination therapy with ESKM and TKIs was superior to either drug alone, capable of curing mice. ESKM showed no toxicity to human HLA-A*02:01(+) stem cells under the conditions of this murine model. These features of ESKM make it a promising nontoxic therapeutic agent for sensitive and resistant Ph(+) leukemias.

Zinc co-ordination by the DHHC cysteine-rich domain of the palmitoyltransferase Swf1

S-acylation, commonly known as palmitoylation, is a widespread post-translational modification of proteins that consists of the thioesterification of one or more cysteine residues with fatty acids. This modification is catalysed by a family of PATs (palmitoyltransferases), characterized by the presence of a 50-residue long DHHC-CRD (Asp-His-His-Cys cysteine-rich domain). To gain knowledge on the structure-function relationships of these proteins, we carried out a random-mutagenesis assay designed to uncover essential amino acids in Swf1, the yeast PAT responsible for the palmitoylation of SNARE (soluble N-ethylmaleimide-sensitive fusion protein-attachment protein receptor) proteins. We identified 21 novel loss-of-function mutations, which are mostly localized within the DHHC-CRD. Modelling of the tertiary structure of the Swf1 DHHC domain suggests that it could fold as a zinc-finger domain, co-ordinating two zinc atoms in a CCHC arrangement. All residues predicted to be involved in the co-ordination of zinc were found to be essential for Swf1 function in the screen. Moreover, these mutations result in unstable proteins, in agreement with a structural role for these zinc fingers. The conservation of amino acids predicted to form each zinc-binding pocket suggests a shared function, as the selective pressure to maintain them is lost upon mutation of one of them. A Swf1 orthologue that lacks one of the zinc-binding pockets is able to complement a yeast swf1∆ strain, possibly because a similar fold can be stabilized by hydrogen bonds instead of zinc co-ordination. Finally, we show directly that recombinant Swf1 DHHC-CRD is able to bind zinc. Sequence analyses of DHHC domains allowed us to present models of the zinc-binding properties for all PATs.

The involvement of WT1 in the regulation of GADD45a in response to genotoxic stress

Expression of the human GADD45a gene is increased in TK6 cells exposed to mutagens, clastogens and aneugens. It is known to be regulated through both p53-dependent and p53-independent pathways and WT1 has been implicated in both cases. This article reports an investigation into the effect that mutations in the WT1 and p53 response elements of the gene have on GADD45a expression. This was conducted in both p53 wild-type (TK6) and mutant (WI-L2-NS) human B lymphoblastoid cell lines. Gene expression was monitored using a GADD45a-green fluorescent protein reporter assay. Mutant cell lines were exposed to the mechanistically diverse genotoxins methyl methanesulphonate, cisplatin and mitomycin C (direct acting), hydroxyurea, aphidicolin and 5'fluorouracil (inhibitors of nucleotide/DNA synthesis) and benomyl (aneugen). In all cases, the induction of the reporter was reduced in the mutants compared with wild-type. These results provide experimental evidence for the implied role of WT1 in both p53-dependent and p53-independent pathways of GADD45a regulation and further insight into the mechanism of GADD45a induction by genotoxins.

Specific labeling of zinc finger proteins using noncanonical amino acids and copper-free click chemistry

Zinc finger proteins (ZFPs) play a key role in transcriptional regulation and serve as invaluable tools for gene modification and genetic engineering. Development of efficient strategies for labeling metalloproteins such as ZFPs is essential for understanding and controlling biological processes. In this work, we engineered ZFPs containing cysteine-histidine (Cys2-His2) motifs by metabolic incorporation of the unnatural amino acid azidohomoalanine (AHA), followed by specific protein labeling via click chemistry. We show that cyclooctyne promoted [3 + 2] dipolar cycloaddition with azides, known as copper-free click chemistry, provides rapid and specific labeling of ZFPs at high yields as determined by mass spectrometry analysis. We observe that the DNA-binding activity of ZFPs labeled by conventional copper-mediated click chemistry was completely abolished, whereas ZFPs labeled by copper-free click chemistry retain their sequence-specific DNA-binding activity under native conditions, as determined by electrophoretic mobility shift assays, protein microarrays, and kinetic binding assays based on Förster resonance energy transfer (FRET). Our work provides a general framework to label metalloproteins such as ZFPs by metabolic incorporation of unnatural amino acids followed by copper-free click chemistry.

Kinetic behaviour of WT 1's zinc finger domain in binding to the alpha-actinin-1 mRNA

The zinc finger transcription factor Wilms tumour protein (WT 1) is known for its essential involvement in the development of the genitourinary system as well as of other organs and tissues. WT 1 is capable of selectively binding either DNA or mRNA targets. A KTS insertion due to alternative splicing between the zinc fingers 3 and 4 and an unconventional zinc finger 1 are the unique features that distinguish WT 1 from classical DNA-binding C(2)H(2)-type zinc finger proteins. The DNA binding characteristics of WT 1 are well studied. Due to lack of information about its native RNA targets, no extensive research has been directed at how WT 1 binds RNA. Using surface plasmon resonance, this study attempts to understand the binding behaviour of WT 1 zinc fingers with its recently reported and first putative mRNA target, ACT 34, whose stem-loop structure is believed to be critical for the interactions with WT 1. We have analysed the interactions of five WT 1 zinc finger truncations with wild-type ACT 34 and four variants. Our results indicate that WT 1 zinc fingers bind ACT 34 in a specific manner, and that this occurs as interplay of all four zinc fingers. We also report that a sensitive kinetic balance, which is equilibrated by both zinc finger 1 and KTS, regulates the interaction with ACT 34. The stem-loop and the flanking nucleotides are important elements for specific recognition by WT 1 zinc fingers.

New insights into DNA-binding behavior of Wilms tumor protein (WT1)--a dual study

Wilms Tumor suppressor protein (WT1) is a transcription factor that is involved in a variety of developmental functions during organ development. It is also implicated in the pathology of several different cancer forms. The protein contains four C(2)H(2)-type zinc fingers and it specifically binds GC-rich sequences in the promoter regions of its target genes, which are either up or down regulated. Two properties make WT1 a more unusual transcription factor - an unconventional amino acid composition for zinc finger 1, and the insertion of a tri-peptide KTS in some of the splice isoforms of WT1. Using six WT1 constructs in which zinc fingers are systematically deleted, a dual study based on a bacterial 1-hybrid system and surface plasmon resonance measurements is performed. The experiments show that the effect of zinc finger 1 is not significant in terms of overall DNA-binding kinetics, however it influences both the specificity of target recognition and stability of interaction in presence of KTS. The KTS insertion, however, only mildly retards binding affinity, mainly by affecting the on-rate. We suggest that the insertion disturbs zinc finger 4 from its binding frame, thus weakening the rate of target recognition. Finally, for the construct in which both zinc fingers 1 and 4 were deleted, the two middle fingers 2-3 still could function as a 'minimal DNA-recognition domain' for WT1, however the formation of a stable protein-DNA complex is impaired since the overall affinity was dramatically reduced mainly since the off-rate was severely affected.