One-step purification of mammalian deoxyribonucleases I and differences among pancreas, parotid, and pancreas-parotid (mixed) types based on species-and organ-specific N-linked glycosylation

Engineering a waste management enzyme to overcome cancer resistance to apoptosis: adding DNase1 to the anti-cancer toolbox

Cancer treatment is often complicated by resistance to conventional anti-cancer treatment and to more recently developed immunotherapy and gene therapy. These therapeutic modalities aim at activating death pathways within cancer cells. Attempts to activate the apoptotic death pathway, by overexpressing proapoptotic signals, are compromised by cancer defense mechanisms, which disrupt the apoptotic-signaling cascade downstream of the overexpressed component. Here, we describe a therapeutic option of triggering apoptosis without activating the apoptotic-signaling cascade or using the native apoptosis executioner nuclease. We have engineered Deoxyribonuclease-1 (DNase1), a waste-management enzyme, by deleting its signal peptide, adding a nuclear localization signal, and mutating its actin-binding site. Apoptosis studies and colony-forming assay for assessing cell viability were conducted in apoptosis-resistant Mel-Juso human melanoma cells. The modified DNase1 reduced cell viability by 77% relative to controls. It also induced typical microscopic features of cellular apoptosis, such as Terminal Transferase dUTP Nick-End Labeling-positive cells and DNA fragmentation. Quantification of apoptosis by Laser scanning cytometry demonstrated high-killing efficiency of 70-100%. The results suggest that this modified DNase1 can efficiently eliminate apoptosis-resistant cancer cells through apoptosis. Coupled to different tissue-specific gene expression elements, this recombinant DNase1 may serve as a platform for eliminating a variety of cancer types.

Two deoxyribonuclease I gene polymorphisms and correlation between genotype and its activity in Japanese population

Deoxyribonuclease I (DNase I) plays important roles for DNA fragmentation and degradation during programmed cell death. The single nucleotide polymorphism (SNP) at DNase I, designated as DNASE1, in exon 8 (A2317G) is considered to be one of the susceptibility genes for gastric and colorectal carcinoma and myocardial infarction. Recent research has shown the presence of a novel 56-bp variable number of tandem repeat (VNTR) polymorphism in intron 4 at DNase I, designated as HumDN1. In the present study, DNASE1 and HumDN1polymorphisms and serum DNase I activities in each different genotype were investigated in 137 Japanese populations. The allele frequencies of A and G in DNASE1 were 0.5839 and 0.4161, respectively. The allelic frequencies of alleles 2, 3, 4, and 5 in HumDN1 were 0.0219, 0.5803, 0.2226, and 0.1752, respectively. In the DNASE1 polymorphism, the activities of genotypes GG and AG were significantly higher than that of AA. As for the HumDN1 polymorphism, the activity of genotype 55 was significantly higher than the activities of 33 and 34. In addition, a significant difference was observed between haplotypes AA/33 and GG/55. The analysis of the correlation between genotype and DNase I activity may be potentially useful for clinical purposes.

Single-step Purification by Lectin Affinity and Deglycosylation Analysis of Recombinant Human and Porcine Deoxyribonucleases I Expressed in COS-7 Cells

Human and porcine recombinant deoxyribonucleases I (DNases I) were expressed in COS-7 cells, and purified by a single-step procedure. Since affinities for concanavalin A (Con A) and wheatgerm agglutinin (WGA) were strong in these recombinant DNases I, purification using Con A-WGA mixture-agarose column was performed. By this method, the enzymes in culture medium could quickly be isolated to apparent homogeneity in approx. 10 min. From 1 ml of culture medium, about 20-30 microg of purified DNase I with a specific activity ranging from 22000 to 41000 units/mg were obtained. The purified DNases I were subjected to enzymatic deglycosylation by either peptide N-glycosidase F (PNGase F) or endoglycosidase H (Endo H). The recombinant enzyme was cleaved by PNGase F, but not by Endo H, indicating that the recombinant enzymes are modified by N-linked complex-type carbohydrate moieties. In the human recombinant DNase I, activity was decreased by PNGase F-treatment, while that of the porcine DNase I remained unaffected. The thermal stability of the human enzyme was extremely susceptible to heat following PNGase F-treatment, as was the porcine enzyme to a lesser extent. This study suggests that N-linked complex-type carbohydrate moieties may contribute to the enzymatic activity and/or thermal stability of recombinant DNases I.