[SLFN11 inhibition rescues the Fanconi anemia phenotype by stabilizing stalled replication forks].

Fanconi anemia (FA) is a rare hereditary disorder characterized by hypersensitivity to the interstrand crosslinks (ICLs) induced by cisplatin, mitomycin C, or formaldehyde. We found that inhibition of SLFN11, which has been identified as a dominant determinant of responses to various antitumor drugs such as cisplatin, camptothecin, and PARP inhibitors, rescued ICL sensitivity and partially alleviated FA phenotype by stabilizing replication forks. This suggests that SLFN11 intensifies DNA damage sensitivity in FA cells, and could be a novel therapeutic target for the FA phenotype.

Mouse Slfn8 and Slfn9 genes complement human cells lacking SLFN11 during the replication stress response.

The Schlafen (SLFN)11 gene has been implicated in various biological processes such as suppression of HIV replication, replication stress response, and sensitization of cancer cells to chemotherapy. Due to the rapid diversification of the SLFN family members, it remains uncertain whether a direct ortholog of human SLFN11 exists in mice. Here we show that mSLFN8/9 and hSLFN11 were rapidly recruited to microlaser-irradiated DNA damage tracks.

Fanconi anemia and Aldehyde Degradation Deficiency Syndrome: Metabolism and DNA repair protect the genome and hematopoiesis from endogenous DNA damage.

We have identified a set of Japanese children with hypoplastic anemia caused by combined defects in aldehyde degrading enzymes ADH5 and ALDH2. Their clinical characteristics overlap with a hereditary DNA repair disorder, Fanconi anemia. Our discovery of this disorder, termed Aldehyde Degradation Deficiency Syndrome (ADDS), reinforces the notion that endogenously generated aldehydes exert genotoxic effects; thus, the coupled actions of metabolism and DNA repair are required to maintain proper hematopoiesis and health.

The ribonuclease domain function is dispensable for SLFN11 to mediate cell fate decision during replication stress response.

The SLFN11 gene participates in cell fate decision following cancer chemotherapy and encodes the N-terminal ribonuclease (RNase) domain and the C-terminal helicase/ATPase domain. How these domains contribute to the chemotherapeutic response remains controversial. Here, we expressed SLFN11 containing mutations in two critical residues required for RNase activity in SLFN11 cells.

[Aldehyde degradation deficiency (ADD) syndrome: discovery of a novel fanconi anemia-like inherited BMF syndrome due to combined ADH5/ALDH2 deficiency].

We have recently described the identification of a novel inherited bone marrow failure syndrome. The first set of patients was diagnosed through the exome analysis of cells from Japanese patients with hypoplastic anemia, which have been deposited to the JCRB cell bank for quite some time previously. Originally, these cases were diagnosed with a novel disorder based on increased levels of sister chromatid exchanges in lymphocytes; however, causative genes were clarified only after applying the recently developed next-generation sequencing technology.

Analysis of disease model iPSCs derived from patients with a novel Fanconi anemia-like IBMFS ADH5/ALDH2 deficiency.

We have recently discovered Japanese children with a novel Fanconi anemia-like inherited bone marrow failure syndrome (IBMFS). This disorder is likely caused by the loss of a catabolic system directed toward endogenous formaldehyde due to biallelic variants in ADH5 combined with a heterozygous ALDH2*2 dominant-negative allele (rs671), which is associated with alcohol-induced Asian flushing. Phytohemagglutinin-stimulated lymphocytes from these patients displayed highly increased numbers of spontaneous sister chromatid exchanges (SCEs), reflecting homologous recombination repair of formaldehyde damage.

Two Aldehyde Clearance Systems Are Essential to Prevent Lethal Formaldehyde Accumulation in Mice and Humans.

Reactive aldehydes arise as by-products of metabolism and are normally cleared by multiple families of enzymes. We find that mice lacking two aldehyde detoxifying enzymes, mitochondrial ALDH2 and cytoplasmic ADH5, have greatly shortened lifespans and develop leukemia. Hematopoiesis is disrupted profoundly, with a reduction of hematopoietic stem cells and common lymphoid progenitors causing a severely depleted acquired immune system.

SLFN11 promotes stalled fork degradation that underlies the phenotype in Fanconi anemia cells.

Fanconi anemia (FA) is a hereditary disorder caused by mutations in any 1 of 22 FA genes. The disease is characterized by hypersensitivity to interstrand crosslink (ICL) inducers such as mitomycin C (MMC). In addition to promoting ICL repair, FA proteins such as RAD51, BRCA2, or FANCD2 protect stalled replication forks from nucleolytic degradation during replication stress, which may have a profound impact on FA pathophysiology.

Enhancements of the production of bilirubin and the expression of β-globin by carbon monoxide during erythroid differentiation.

Heme is degraded by heme oxygenase to form iron, carbon monoxide (CO), and biliverdin. However, information about the catabolism of heme in erythroid cells is limited. In this study, we showed the production and export of bilirubin in murine erythroleukemia (MEL) cells.

A simple and highly sensitive method of measuring heme oxygenase activity.

Heme oxygenase (HO) is a rate-limiting step of heme degradation, which catalyzes the conversion of heme into biliverdin, iron, and CO. HO has been characterized in microorganisms, insects, plants, and mammals. Previously used assays of HO activity were complicated and had low sensitivity.

Continuous de novo biosynthesis of haem and its rapid turnover to bilirubin are necessary for cytoprotection against cell damage.

It is well known that haem serves as the prosthetic group of various haemoproteins that function in oxygen transport, respiratory chain, and drug metabolism. However, much less is known about the functions of the catabolites of haem in mammalian cells. Haem is enzymatically degraded to iron, carbon monoxide (CO), and biliverdin, which is then converted to bilirubin.

p53 directly regulates the transcription of the human frataxin gene and its lack of regulation in tumor cells decreases the utilization of mitochondrial iron.

Mitochondrial frataxin functions in iron homeostasis, biogenesis of iron-sulfur clusters, protection from oxidative stress and apoptosis, and as a tumor suppressor protein. We examined regulation of the expression of the human frataxin by p53. Pifithrin-α, an inhibitor of p53 function, and knockdown of p53 decreased the level of frataxin mRNA in human kidney HEK 293T cells.

Neurotransmitter transporter family including SLC6A6 and SLC6A13 contributes to the 5-aminolevulinic acid (ALA)-induced accumulation of protoporphyrin IX and photodamage, through uptake of ALA by cancerous cells.

δ-Aminolevulinic acid (ALA)-induced protoporphyrin accumulation is widely used in the treatment of cancer, as photodynamic therapy (PDT). To clarify the mechanisms of ALA uptake by tumor cells, we have examined the ALA-induced accumulation of protoporphyrin by the treatment of colon cancer DLD-1 and epithelial cancer HeLa cells with γ-aminobutyric acid (GABA)-related compounds. When the cells were treated with GABA, taurine and β-alanine, the level of protoporphyrin was decreased, suggesting that plasma membrane transporters involved in the transport of neurotransmitters contribute to the uptake of ALA.

Imaging of heme/hemeproteins in nucleus of the living cells expressing heme-binding nuclear receptors.

Several factors involved in the core circadian rhythm are PAS domain proteins, one of which, neuronal PAS2 (NPAS2), contains a heme-binding motif. It is thought that heme controls the transcriptional activity of core circadian factors BMAL1-NPAS2, and that the heme-binding nuclear receptor REV-erbα negatively regulates the expression of BMAL1. To examine the role of heme in the nucleus, we expressed nuclear hemeproteins including the nuclear localization signal-added cytoglobin, NPAS2 and REV-erbα.