Biology subjects

Maizels, N.

Publications and source records attributed to Maizels, N..

3 recordsLinked to original sources

bioRxiv2019

G-quadruplexes sequester free heme in living cells

Heme is an essential cofactor for many enzymes, but free heme is toxic and its levels are tightly regulated. G-quadruplexes bind heme avidly in vitro, raising the possibility that they may sequester heme in vivo. If so, then treatment that displaces heme from quadruplexes is predicted to induce expression of genes involved in iron and heme homeostasis. Here we show that PhenDC3, a G-quadruplex ligand structurally unrelated to heme, displaces quadruplex-bound heme in vitro and alters transcription in cultured human cells, up-regulating genes that support heme degradation and iron homeostasis, and most strikingly causing a 30-fold induction of heme oxidase 1, the key enzyme in heme degradation. We propose that G-quadruplexes sequester heme to protect cells from the pathophysiological consequences of free heme. This identifies a new function for G-quadruplexes and a new mechanism for protection of cells from heme.

genomics↗

bioRxiv2019

DONOR-FREE GENE CORRECTION BY TARGETED INTERHOMOLOG RECOMBINATION

Spontaneous gene correction by interhomolog recombination (IHR) occasionally occurs to ameliorate genetic diseases of blood and skin1-3. Using an engineered endogenous gene as a reporter, we demonstrate that gene correction by IHR is normally infrequent ([≤]0.02%) but is stimulated by DSBs targeted by CRISPR/Cas9 to both homologous chromosomes; reaching frequencies of 0.5%. We further show that depletion of POLQ stimulates IHR frequencies 4-fold, to 2%, and promotes IHR in G2 phase, when recombination between replicated homologs can correct not only compound heterozygous but also autosomal dominant "gain-of-function" mutations, which present a special challenge for gene therapy. The strategies reported here will enable optimization of IHR for gene therapy in a variety of cell types. Advantages include the ability to correct gain-of-function mutations, no need for an exogenous donor, and the potential to limit damage to coding sequence by targeting IHR to introns.

genetics↗

bioRxiv2019

Treatment with 5-aza-dC Induces Apoptotic PARP1-DNA Adducts

The nucleoside analog 5-aza-2-deoxycytidine (5-aza-dC) is used to treat some hematopoietic malignancies. The mechanism of cell killing depends upon DNMT1, but is otherwise not clearly defined. Here we show that PARP1 forms covalent DNA adducts in human lymphoblast or fibroblasts treated with 5-aza-dC. Some adducts recovered from 5-aza-dC-treated cells have undergone cleavage by apoptotic caspases 3/7. Mapping of PARP1-DNA adducts, by a new method, "Adduct-Seq", demonstrates adduct enrichment at CpG-dense genomic locations that are targets of maintenance methylation by DNMT1. Covalent protein-DNA adducts can arrest replication and induce apoptosis, and these results raise the possibility that induction of PARP1-DNA adducts may contribute to cell killing in response to treatment with 5-aza-dC.

biochemistry↗