The 1.85 A crystal structure of endonuclease III, combined with mutational analysis, suggests the structural basis for the DNA binding and catalytic activity of the enzyme. Helix‐hairpin‐helix (HhH) and [4Fe‐4S] cluster loop (FCL) motifs, which we have named for their secondary structure, bracket the cleft separating the two alpha‐helical domains of the enzyme. These two novel DNA binding motifs and the solvent‐filled pocket in the cleft between them all lie within a positively charged and sequence‐conserved surface region. Lys120 and Asp138, both shown by mutagenesis to be catalytically important, lie at the mouth of this pocket, suggesting that this pocket is part of the active site. The positions of the HhH motif and protruding FCL motif, which contains the DNA binding residue Lys191, can accommodate B‐form DNA, with a flipped‐out base bound within the active site pocket. The identification of HhH and FCL sequence patterns in other DNA binding proteins suggests that these motifs may be a recurrent structural theme for DNA binding proteins.

One factor limiting the therapeutic efficacy of cord blood (CB) hematopoietic progenitor cell (HPC) transplantation is the low cell dose of the graft. This is associated with an increased incidence of delayed or failed engraftment. Cell dose can be increased and the efficacy of CB transplantation potentially improved, by ex vivo CB expansion before transplantation. Two ex vivo CB expansion techniques were compared: (1) CD133 þ selection followed by ex vivo liquid culture and (2) co-culture of unmanipulated CB with bone-marrow-derived mesenchymal stem cells (MSCs). Ex vivo culture was performed in medium supplemented with granulocyte colony-stimulating factor, stem cell factor and either thrombopoietin or megakaryocyte growth and differentiation factor. Expansion was followed by measuring total nucleated cell (TNC), CD133 þ and CD34 þ cell, colony-forming unit and cobblestone area-forming cell output. When compared to liquid culture, CB-MSC co-culture (i) required less cell manipulation resulting in less initial HPC loss and (ii) markedly improved TNC and HPC output. CB-MSC coculture therefore holds promise for improving engraftment kinetics in CB transplant recipients.

No abstract

CCAAT displacement protein (cux/CDP) is an atypical homeodomain protein that represses expression of several developmentally regulated lymphoid and myeloid genes in vitro, including gp91-phox, immunoglobulin heavy chain, the T-cell receptor ␤ and ␥ chains, and CD8. To determine how this activity affects cell development in vivo, a hypomorphic allele of cux/CDP was created by gene targeting. Homozygous mutant mice (cux/ CDP ⌬HD/⌬HD ) demonstrated a partial neonatal lethality phenotype. Surviving animals suffered from a wasting disease, which usually resulted in death between 2 and 3 weeks of age. Analysis of T lymphopoiesis demonstrated that cux/CDP ⌬HD/⌬HD mice had dramatically reduced thymic cellularity due to enhanced apoptosis, with a preferential loss of CD4 ؉ CD8 ؉ thymocytes. Ectopic CD25 expression was also observed in maturing thymocytes. B lymphopoiesis was also perturbed, with a 2-to 3-fold reduction in total bone marrow B-lineage cells and a preferential loss of cells in transition from pro-B/pre-BI to pre-BII stages due to enhanced apoptosis. These lymphoid abnormalities were independent of effects related to antigen receptor rearrangement. In contrast to the lymphoid demise, cux/CDP ⌬HD/⌬HD mice demonstrated myeloid hyperplasia. Bone marrow reconstitution experiments identified that many of the hematopoietic defects were linked to microenvironmental effects, suggesting that underexpression of survival factors or overexpression of death-inducing factors accounted for the phenotypes observed. Tumor necrosis factor (TNF) levels were elevated in several tissues, especially thymus, suggesting that TNF may be a target gene for cux/CDP-mediated repression. These data suggest that cux/CDP regulates normal hematopoiesis, in part, by modulating the levels of survival and/or apoptosis factors expressed by the microenvironment. (Blood. 2001;98:3658-3667)

No abstract

We purified a homologue of the Escherichia coli DNA repair enzyme endo nuclease III 5000-fold from calf thymus which, like endonuclease III, demonstrates DNA-glycosylase activity against pyrimidine hydrates and thymine glycol and AP lyase activity (DNA strand cleavage at AP sites via beta-elimination). The functional similarity between the enzymes suggested a strategy for definitive identification of the bovine protein based on the nature of its enzyme-substrate (ES) intermediate. Prokaryotic DNA glycosylase/AP lyases function through N-acylimine (Schiff's base) ES intermediates which, upon chemical reduction to stable secondary amines, irreversibly cross link the enzyme to oligodeoxynucleotides containing substrate modified bases. We incubated endonuclease III with a 32P- labeled thymine glycol-containing oligodeoxynucleotide in the presence of NaCNBH3. This resulted in an increase in the apparent molecular weight of the enzyme by SDS-PAGE. Phosphorimaging confirmed irreversible cross linking between enzyme and DNA. Identical treatment of the most purified bovine enzyme fraction resulted in irreversible cross linking of the oligodeoxynucleotide to a predominant 31 kDa species. Amino acid analysis of the 31 kDa species revealed homology to the predicted amino acid sequence of a Caenorhabditis elegans 27.8 kDa protein which, in turn, has homology to endonuclease III. The translated amino acid sequences of two partial 3' cDNAs, from Homo sapiens and Rattus sp., also demonstrate homology to the C. elegans and bovine sequences suggesting a homologous family of endonuclease III-like DNA repair enzymes is present throughout phylogeny.

Delayed engraftment remains a major hurdle following cord blood (CB) transplantation. It may be due, at least in part, to low fucosylation of cell surface molecules important for homing to the BM microenvironment. Since fucosylation of specific cell surface ligands is required before effective interaction with selectins expressed by the BM microvasculature can occur, a simple 30 minute ex vivo incubation of CB HPC with fucosyltransferase (FT) - VI and its substrate (GDP-fucose) was performed to increase levels of fucosylation. The physiologic impact of CB HPC hypo-fucosylation was investigated in vivo in NOD-SCID IL-2Rγnull (NSG) mice. By isolating fucosylated and non-fucosylated CD34+ cells from CB we show that only fucosylated CD34+ cells are responsible for engraftment in NSG mice. Further, since the proportion of CD34+ cells that are fucosylated in CB is significantly less than in BM and PB, we hypothesize that these combined observations might explain, at least in part, the delayed engraftment observed following CB transplantation. Since engraftment appears to be correlated with the fucosylation of CD34+ cells, we hypothesized that increasing the proportion of CD34+ cells that are fucosylated would improve CB engraftment. Ex vivo treatment with fucosyltransferase (FT)-VI significantly increases the levels of CD34+ fucosylation and, as hypothesized, this was associated with improved engraftment. Ex vivo fucosylation did not alter the biodistribution of engrafting cells, or pattern of long-term, multi-lineage, multi-tissue engraftment. We propose that ex vivo fucosylation will similarly improve the rate and magnitude of engraftment for CB transplant recipients in a clinical setting.

No abstract