No abstract

Genome damage and defective repair are etiologically linked to neurodegeneration. However, the specific mechanisms involved remain enigmatic. Here, we identify defects in DNA nick ligation and oxidative damage repair in a subset of amyotrophic lateral sclerosis (ALS) patients. These defects are caused by mutations in the RNA/DNA-binding protein FUS. In healthy neurons, FUS protects the genome by facilitating PARP1-dependent recruitment of XRCC1/DNA Ligase IIIα (LigIII) to oxidized genome sites and activating LigIII via direct interaction. We discover that loss of nuclear FUS caused DNA nick ligation defects in motor neurons due to reduced recruitment of XRCC1/LigIII to DNA strand breaks. Moreover, DNA ligation defects in ALS patient-derived iPSC lines carrying FUS mutations and in motor neurons generated therefrom are rescued by CRISPR/Cas9-mediated correction of mutation. Our findings uncovered a pathway of defective DNA ligation in FUS-linked ALS and suggest that LigIII-targeted therapies may prevent or slow down disease progression.

HIV-infected individuals currently cannot be completely cured because existing antiviral therapy regimens do not address HIV provirus DNA, flanked by long terminal repeats (LTRs), already integrated into host genome. Here, we present a possible alternative therapeutic approach to specifically and directly mediate deletion of the integrated full-length HIV provirus from infected and latently infected human T cell genomes by using specially designed zinc-finger nucleases (ZFNs) to target a sequence within the LTR that is well conserved across all clades. We designed and screened one pair of ZFN to target the highly conserved HIV-1 5′-LTR and 3′-LTR DNA sequences, named ZFN-LTR. We found that ZFN-LTR can specifically target and cleave the full-length HIV-1 proviral DNA in several infected and latently infected cell types and also HIV-1 infected human primary cells in vitro. We observed that the frequency of excision was 45.9% in infected human cell lines after treatment with ZFN-LTR, without significant host-cell genotoxicity. Taken together, our data demonstrate that a single ZFN-LTR pair can specifically and effectively cleave integrated full-length HIV-1 proviral DNA and mediate antiretroviral activity in infected and latently infected cells, suggesting that this strategy could offer a novel approach to eradicate the HIV-1 virus from the infected host in the future.

Genome damage and their defective repair have been etiologically linked to degenerating neurons in many subtypes of amyotrophic lateral sclerosis (ALS) patients; however, the specific mechanisms remain enigmatic. The majority of sporadic ALS patients feature abnormalities in the transactivation response DNA-binding protein of 43 kDa (TDP-43), whose nucleo-cytoplasmic mislocalization is characteristically observed in spinal motor neurons. While emerging evidence suggests involvement of other RNA/DNA binding proteins, like FUS in DNA damage response (DDR), the role of TDP-43 in DDR has not been investigated. Here, we report that TDP-43 is a critical component of the nonhomologous end joining (NHEJ)-mediated DNA double-strand break (DSB) repair pathway. TDP-43 is rapidly recruited at DSB sites to stably interact with DDR and NHEJ factors, specifically acting as a scaffold for the recruitment of break-sealing XRCC4-DNA ligase 4 complex at DSB sites in induced pluripotent stem cell-derived motor neurons. shRNA or CRISPR/Cas9-mediated conditional depletion of TDP-43 markedly increases accumulation of genomic DSBs by impairing NHEJ repair, and thereby, sensitizing neurons to DSB stress. Finally, TDP-43 pathology strongly correlates with DSB repair defects, and damage accumulation in the neuronal genomes of sporadic ALS patients and inCaenorhabditis elegansmutant with TDP-1 loss-of-function. Our findings thus link TDP-43 pathology to impaired DSB repair and persistent DDR signaling in motor neuron disease, and suggest that DSB repair-targeted therapies may ameliorate TDP-43 toxicity-induced genome instability in motor neuron disease.

Speckle-type POZ protein (SPOP) is an adaptor of the cullin 3-based ubiquitin ligase responsible for the degradation of oncoproteins frequently overexpressed in many tumor cells. Altered expression and somatic mutations of SPOP have been observed in various tumor types with chromosomal aberrations, indicating a role of SPOP in maintaining genome stability, although a detailed mechanism remains unclear. Here, we show that SPOP is a component of the DNA damage response (DDR). SPOP is recruited to DNA double-strand break sites and it forms nuclear foci after DNA damage. SPOP foci colocalize with γ-H2AX foci and are predominantly dependent on the activity of the ataxia-telangiectasia mutated (ATM) kinase. Furthermore, SPOP interacts with ATM in response to DNA damage. Finally, we demonstrate that knocking down of SPOP resulted in an impaired DDR and a hypersensitivity to ionizing irradiation. Together, we highlight a critical role of SPOP in the DDR.

Dominant mutations in the RNA/DNA-binding protein TDP-43 have been linked to amyotrophic lateral sclerosis (ALS). Here, we screened genomic DNA extracted from spinal cord specimens of sporadic ALS patients for mutations in the TARDBP gene and identified a patient specimen with previously reported Q331K mutation. The patient spinal cord tissue with Q331K mutation showed accumulation of higher levels of DNA strand breaks and the DNA double-strand break (DSB) marker γH2AX, compared to age-matched controls, suggesting a role of the Q331K mutation in genome-damage accumulation. Using conditional SH-SY5Y lines ectopically expressing wild-type (WT) or Q331K-mutant TDP-43, we confirmed the increased cytosolic sequestration of the poly-ubiquitinated and aggregated form of mutant TDP-43, which correlated with increased genomic DNA strand breaks, activation of the DNA damage response factors phospho-ataxia-telangiectasia mutated (ATM), phospho-53BP1, γH2AX and neuronal apoptosis. We recently reported the involvement of WT TDP-43 in non-homologous end joining (NHEJ)-mediated DSB repair, where it acts as a scaffold for the recruitment of XRCC4-DNA ligase 4 complex. Here, the mutant TDP-43, due to its reduced interaction and enhanced cytosolic mislocalization, prevented the nuclear translocation of XRCC4-DNA ligase 4. Consistently, the mutant cells showed significantly reduced DNA strand break sealing activity and were sensitized to DNA-damaging drugs. In addition, the mutant cells showed elevated levels of reactive oxygen species, suggesting both dominant negative and loss-of-function effects of the mutation. Together, our study uncovered an association of sporadic Q331K mutation with persistent genome damage accumulation due to both damage induction and repair defects.

The malaria parasite Plasmodium falciparum exports a large number of proteins into the erythrocyte cytoplasm during the asexual intraerythrocytic stage of its life cycle. A subset of these proteins interacts with erythrocyte membrane skeletal proteins and grossly alters the structure and function of the membrane. Several of the exported proteins, such as PfEMP1, PfEMP3, RESA and KAHRP, interact with the preponderant erythrocyte skeleton protein, spectrin. Here we have searched for possible interaction of these four malaria proteins with another major erythrocyte skeleton protein, ankyrin R. We have shown that KAHRP, but none of the other three, binds to ankyrin R. We have mapped the binding site for ankyrin R to a 79-residue segment of the KAHRP sequence, and the reciprocal binding site for KAHRP in ankyrin R to a subdomain (D3) of the 89 kDa ankyrin R membrane-binding domain. Interaction of intact ankyrin R with KAHRP was inhibited by the free D3 subdomain. When, moreover, red cells loaded with the soluble D3 subdomain were infected with P. falciparum, KAHRP secreted by the intraerythrocytic parasite no longer migrated to the host cell membrane, but remained diffusely distributed throughout the cytosol. Our findings suggest a potentially important role for interaction of KAHRP with red cell membrane skeleton in promoting the adhesion of malaria-infected red cells to endothelial surfaces, a central element in the pathophysiology of malaria.

Liver tumor-initiating cells (TICs), the drivers for liver tumorigenesis, accounts for liver tumor initiation, metastasis, drug resistance and relapse. Wnt/β-catenin signaling pathway emerges as a critical modulator in liver TIC self-renewal. However, the molecular mechanism of Wnt/β-catenin initiation in liver tumorigenesis and liver TICs is still elusive. Here, we examined the expression pattern of 10 Wnt receptors (FZD1–FZD10), and found only FZD6 is overexpressed along with liver tumorigenesis. What’s more, a divergent lncRNA of FZD6, termed lncFZD6, is also highly expressed in liver cancer and liver TICs. LncFZD6 drives liver TIC self-renewal and tumor initiation capacity through FZD6-dependent manner. LncFZD6 interacts with BRG1-embedded SWI/SNF complex and recruits it to FZD6 promoter, and thus drives the transcriptional initiation of FZD6 by chromatin remodeling. WNT5A, a ligand of FZD6, is highly expressed in liver non-TICs and drives the self-renewal of liver TICs through lncFZD6-BRG1-FZD6-dependent manner. Through FZD6 transcriptional regulation in cis, lncFZD6 activates Wnt/β-catenin signaling in liver TICs. LncFZD6-BRG1-Wnt5A/β-catenin pathway can serve as a target for liver TIC elimination. Altogether, lncFZD6 promotes Wnt/β-catenin activation and liver TIC self-renewal through BRG1-dependent FZD6 expression.