Many neurodegenerative disorders are caused by abnormal accumulation of misfolded proteins. In spinocerebellar ataxia type 1 (SCA1), accumulation of polyglutamine-expanded (polyQ-expanded) ataxin-1 (ATXN1) causes neuronal toxicity. Lowering total ATXN1, especially the polyQ-expanded form, alleviates disease phenotypes in mice, but the molecular mechanism by which the mutant ATXN1 is specifically modulated is not understood. Here, we identified 22 mutant ATXN1 regulators by performing a cross-species screen of 7787 and 2144 genes in human cells and Drosophila eyes, respectively. Among them, transglutaminase 5 (TG5) preferentially regulated mutant ATXN1 over the WT protein. TG enzymes catalyzed cross-linking of ATXN1 in a polyQ-length–dependent manner, thereby preferentially modulating mutant ATXN1 stability and oligomerization. Perturbing Tg in Drosophila SCA1 models modulated mutant ATXN1 toxicity. Moreover, TG5 was enriched in the nuclei of SCA1-affected neurons and colocalized with nuclear ATXN1 inclusions in brain tissue from patients with SCA1. Our work provides a molecular insight into SCA1 pathogenesis and an opportunity for allele-specific targeting for neurodegenerative disorders.
Won-Seok Lee, Ismael Al-Ramahi, Hyun-Hwan Jeong, Youjin Jang, Tao Lin, Carolyn J. Adamski, Laura A. Lavery, Smruti Rath, Ronald Richman, Vitaliy V. Bondar, Elizabeth Alcala, Jean-Pierre Revelli, Harry T. Orr, Zhandong Liu, Juan Botas, Huda Y. Zoghbi
BACKGROUND. Tuberous Sclerosis Complex (TSC) is a neurogenetic syndrome due to loss-of-function mutations in TSC2 or TSC1, characterized by tumors at multiple body sites, including facial angiofibroma (FAF). Here, an ultrasensitive assessment of the extent and range of UV-induced mutations in TSC facial skin was performed. METHODS. A Multiplex High-sensitivity PCR Assay (MHPA) was developed, enabling mutation detection at extremely low (<0.1%) variant allele frequencies (VAF). RESULTS. MHPA assays were developed for both TSC2 and TP53, and applied to 81 samples, including 66 skin biopsies. UV-induced second hit mutation causing inactivation of TSC2 was pervasive in TSC facial skin with an average of 4.8 mutations per 2 mm biopsy at median VAF 0.08%, generating >150,000 incipient facial tumors (subclinical ‘micro-FAFs’) in the average TSC subject. The MHPA analysis also led to the identification of a refined UV-related indel signature and a recurrent complex mutation pattern, consisting of both a single or dinucleotide variant, and a 1-9 nt deletion, in cis. CONCLUSION. TSC facial skin can be viewed as harboring a patchwork of clonal fibroblast proliferations (micro-FAF) with indolent growth, a small proportion of which develop into clinically observable FAF. Our observations also expand the spectrum of UV-related mutation signatures. FUNDING. This work was supported by the TSC Alliance, Engles Family Fund for Research in TSC and LAM, and National Institutes of Health, National Heart, Lung, and Blood Institute [U01HL131022-04; Intramural Research Program].
Katarzyna Klonowska, Joannes M. Grevelink, Krinio Giannikou, Barbara A. Ogorek, Zachary T. Herbert, Aaron R. Thorner, Thomas N. Darling, Joel Moss, David J. Kwiatkowski
Host defense and inflammation are regulated by the NF-κB essential modulator (NEMO), a scaffolding protein with a broad immune cell and tissue expression profile. Hypomorphic mutations in inhibitor of NF-κB kinase regulatory subunit gamma (IKBKG) encoding NEMO typically present with immunodeficiency. Here, we characterized a pediatric autoinflammatory syndrome in 3 unrelated male patients with distinct X-linked IKBKG germline mutations that led to overexpression of a NEMO protein isoform lacking the domain encoded by exon 5 (NEMO-Δex5). This isoform failed to associate with TANK binding kinase 1 (TBK1), and dermal fibroblasts from affected patients activated NF-κB in response to TNF but not TLR3 or RIG-I–like receptor (RLR) stimulation when isoform levels were high. By contrast, T cells, monocytes, and macrophages that expressed NEMO-Δex5 exhibited increased NF-κB activation and IFN production, and blood cells from these patients expressed a strong IFN and NF-κB transcriptional signature. Immune cells and TNF-stimulated dermal fibroblasts upregulated the inducible IKK protein (IKKi) that was stabilized by NEMO-Δex5, promoting type I IFN induction and antiviral responses. These data revealed how IKBKG mutations that lead to alternative splicing of skipping exon 5 cause a clinical phenotype we have named NEMO deleted exon 5 autoinflammatory syndrome (NDAS), distinct from the immune deficiency syndrome resulting from loss-of-function IKBKG mutations.
Younglang Lee, Alex W. Wessel, Jiazhi Xu, Julia G. Reinke, Eries Lee, Somin M. Kim, Amy P. Hsu, Jevgenia Zilberman-Rudenko, Sha Cao, Clinton Enos, Stephen R. Brooks, Zuoming Deng, Bin Lin, Adriana A. de Jesus, Daniel N. Hupalo, Daniela G.P. Piotto, Maria T. Terreri, Victoria R. Dimitriades, Clifton L. Dalgard, Steven M. Holland, Raphaela Goldbach-Mansky, Richard M. Siegel, Eric P. Hanson
Genetic variants at the SORT1 locus in humans causing increased SORT1 expression in liver are significantly associated with reduced plasma levels of LDL cholesterol and apolipoprotein B (apoB). However, the role of hepatic sortilin remains controversial, as genetic deletion of sortilin in mice has yielded variable and conflicting effects on apoB secretion. Sort1 knockout mice on a chow diet and several Sort1-deficient hepatocyte lines displayed no difference in apoB secretion. When these models were challenged with high fat or ER stress, the loss of Sort1 expression resulted in a significant increase in apoB-100 secretion. Sort1 overexpression studies yielded reciprocal results. Importantly, diabetic carriers of SORT1 variant have larger decreases in plasma apoB, TG, and VLDL and LDL particle number as compared to non-diabetics with the same variants. We conclude that under basal non-stressed conditions, loss of sortilin has little effect on hepatocyte apoB secretion, but that in the setting of lipid-loading or ER stress, sortilin deficiency leads to increased apoB secretion. These results are consistent with the directionality of effect in human genetics studies and suggest that under stress conditions, hepatic sortilin directs apoB toward lysosomal degradation rather than secretion, potentially serving as a quality control step in the apoB secretion pathway in hepatocytes.
Donna M. Conlon, Carolin V. Schneider, Yi-An Ko, Amrith Rodrigues, Kathy Guo, Nicholas J. Hand, Daniel J. Rader
Despite being the first homolog of the bacterial RecQ helicase to be identified in humans the function of RECQL1 remains poorly characterised. Furthermore, unlike other members of the human RECQ family of helicases, mutations in RECQL1 have not been associated with a genetic disease. Here we identify two families with a novel genome instability disorder, named RECON (RECql ONe) Syndrome caused by biallelic mutations in the RECQL gene. The affected individuals exhibit short stature, progeroid facial features, a hypoplastic nose, xeroderma and skin photosensitivity. Affected individuals were homozygous for the same missense mutation in RECQL1 (p.Ala459Ser) located within its zinc binding domain. Biochemical analysis of the mutant RECQL1 protein revealed that the p.A459S missense mutation compromised its ATPase, helicase and fork restoration activity, whilst its capacity to promote single-strand DNA annealing was largely unaffected. At the cellular level, this mutation in RECQL1 gave rise to a defect in the ability to repair DNA damage induced by exposure to topoisomerase poisons and a failure of DNA replication to progress efficiently in the presence of abortive topoisomerase lesions. Taken together, RECQL1 is the fourth member of the RecQ family of helicases to be associated with a human genome instability disorder.
Bassam Abu-Libdeh, Satpal S. Jhujh, Srijita Dhar, Joshua A. Sommers, Arindam Datta, Gabriel M.C. Longo, Laura J. Grange, John J. Reynolds, Sophie L. Cooke, Gavin S. McNee, Robert Hollingworth, Beth L. Woodward, Anil N. Ganesh, Stephen J. Smerdon, Claudia M. Nicolae, Karina Durlacher-Betzer, Vered Molho-Pessach, Abdulsalam Abu-Libdeh, Vardiella Meiner, George-Lucian Moldovan, Vassilis Roukos, Tamar Harel, Robert M. Brosh Jr., Grant S. Stewart
Inherited germline mutations in the BRCA1 (BReast CAncer gene 1) or BRCA2 (BReast CAncer gene 2) genes (herein BRCA1/2) greatly increase the risk of breast and ovarian cancer, presumably by elevating somatic mutational errors as a consequence of deficient DNA repair. However, this has never been directly demonstrated by a comprehensive analysis of the somatic mutational landscape of primary, non-cancer, mammary epithelial cells of women diagnosed with pathogenic BRCA1 or BRCA2 germline mutations. Here we used an accurate, single-cell whole genome sequencing approach to first show that telomerized primary mammary epithelial cells heterozygous for a highly penetrant BRCA1 variant displayed a robustly elevated mutation frequency as compared to their isogenic control cells. We then demonstrated a small but statistically significant increase in mutation frequency in mammary epithelial cells isolated from the breast of BRCA1/2 mutation carriers as compared to those obtained from age-matched controls with no genetically increased risk for breast cancer.
Shixiang Sun, Kristina Brazhnik, Moonsook Lee, Alexander Y. Maslov, Yi Zhang, Zhenqiu Huang, Susan Klugman, Ben H. Park, Jan Vijg, Cristina Montagna
The KRAS proto-oncogene is among the most frequently mutated genes in cancer, yet for 40 years it remained an elusive therapeutic target. Recently, allosteric inhibitors that covalently bind to KRAS G12C mutations have been approved for use in lung adenocarcinomas. Although responses are observed they are often short-lived, thus making in-depth characterization of the mechanisms of resistance of paramount importance. Here, we present a rapid-autopsy case of a patient who had a KRASG12C-mutant lung adenocarcinoma who initially responded to a KRAS G12C inhibitor but then rapidly developed resistance. Using deep RNA and whole exome sequencing comparing pre-treatment, post-treatment and matched normal tissues, we uncover numerous mechanisms of resistance to direct KRAS inhibition. In addition to decreased KRAS G12C mutant allele frequency in refractory tumors, we also found reactivation of the MAPK pathway despite no new mutations in KRAS or its downstream mediators. Tumor cell intrinsic and non-cell autonomous mechanisms included increased complement activation, coagulation and tumor angiogenesis, and several lines of evidence of immunologic evasion. Together, our findings reveal numerous mechanisms of resistance to current KRAS G12C inhibitors through enrichment of clonal populations, KRAS-independent downstream signaling and diverse remodeling of the tumor microenvironment.
Yihsuan S. Tsai, Mark G. Woodcock, Salma H. Azam, Leigh B. Thorne, Krishna L. Kanchi, Joel S. Parker, Benjamin G Vincent, Chad V. Pecot
We investigated the interplay between genetics and oral peanut protein exposure in the determination of the immunological response to peanut using the targeted intervention in the LEAP clinical trial. We identified an association between peanut-specific IgG4 and HLA-DQA1*01:02 that was only observed in the presence of sustained oral peanut protein exposure. The association between IgG4 and HLA-DQA1*01:02 was driven by IgG4 specific for the Ara h 2 component. Once peanut consumption ceased, the association between IgG4-specific Ara h 2 and HLA-DQA1*01:02 was attenuated. The association was validated by observing expanded IgG4-specific epitopes in people who carried HLA-DQA1*01:02. Notably, we confirmed the previously reported associations with HLA-DQA1*01:02 and peanut allergy risk in the absence of oral peanut protein exposure. Interaction between HLA and presence or absence of exposure to peanut in an allergen- and epitope-specific manner implicates a mechanism of antigen recognition that is fundamental to driving immune responses related to allergy risk or protection.
Kanika Kanchan, Stepan Grinek, Henry T. Bahnson, Ingo Ruczinski, Gautam Shankar, David Larson, George Du Toit, Kathleen C. Barnes, Hugh A. Sampson, Mayte Suarez-Farinas, Gideon Lack, Gerald T. Nepom, Karen Cerosaletti, Rasika A. Mathias
Mantle cell lymphoma (MCL) is a phenotypically and genetically heterogeneous malignancy in which the genetic alterations determining clinical behavior are not fully understood. Here we performed a comprehensive whole-exome sequencing analysis of 152 primary samples derived from 134 MCL patients, including longitudinal samples from 16 patients and matched RNA sequencing data from 48 samples. We classified MCL into four robust clusters (C). C1 featured mutated IGHV, CCND1 mutation, amp(11q13) and active BCR signaling. C2 was enriched with del(11q)/ATM mutations and upregulation of NF-κB and DNA repair pathways. C3 was characterized by mutations in SP140, NOTCH1 and NSD2 with downregulation of BCR signaling and MYC targets. C4 harbored del(17p)/TP53 mutations, del(13q) and del(9p), and active MYC pathway and hyperproliferation signatures. Patients in these four clusters had distinct outcomes (5-year OS rates for C1-C4 were 100%, 56.7%, 48.7%, and 14.2%, respectively, p<0.001). We also inferred the temporal order of genetic events and studied clonal evolution of 16 patients before treatment and at progression/relapse. Eleven of these samples showed drastic clonal evolution that was associated with inferior survival while the other samples showed modest or no evolution. Our study thus identifies genetic subsets that clinically define this malignancy and delineates clonal evolution patterns and their impact on clinical outcomes.
Shuhua Yi, Yuting Yan, Meiling Jin, Supriyo Bhattacharya, Yi Wang, Yiming Wu, Lu Yang, Eva Giné, Guillem Clot, Lu Chen, Ying Yu, Dehui Zou, Jun Wang, An T. Phan, Rui Cui, Fei Li, Qi Sun, Qiongli Zhai, Tingyu Wang, Zhen Yu, Lanting Liu, Wei Liu, Rui Lyv, Weiwei Sui, Wenyang huang, Wenjie Xiong, Huijun Wang, Chengwen Li, Zhijian Xiao, Mu Hao, Jianxiang Wang, Tao Cheng, Silvia Bea, Alex F. Herrera, Alexey Danilov, Elias Campo, Vu N. Ngo, Lugui Qiu, Lili Wang
Genetic variants near the TRIB1 gene are highly significantly associated with plasma lipid traits and coronary artery disease. While TRIB1 is likely causal of these associations, the molecular mechanisms are not well understood. Here we sought to investigate how TRIB1 influences low density lipoprotein cholesterol (LDL-C) levels in mice. Hepatocyte-specific deletion of Trib1 (Trib1Δhep) in mice increased plasma cholesterol and apoB and slowed the catabolism of LDL-apoB due to decreased levels of LDL receptor (LDLR) mRNA and protein. Simultaneous deletion of the transcription factor CCAAT/enhancer-binding protein alpha (CEBPα) with TRIB1 eliminated the effects of TRIB1 on hepatic LDLR regulation and LDL catabolism. Using RNA-seq, we found that activating transcription factor 3 (Atf3) was highly upregulated in the livers of Trib1Δhep but not Trib1Δhep CebpaΔhep mice. ATF3 has been shown to directly bind to the CEBPα protein, and to repress the expression of LDLR by binding its promoter. Blunting the increase of ATF3 in Trib1Δhep mice reduced the levels of plasma cholesterol and partially attenuated the effects on LDLR. Based on these data, we conclude that deletion of Trib1 leads to a posttranslational increase in CEBPα, which increases ATF3 levels, thereby contributing to the downregulation of LDLR and increased plasma LDL-C.
Katherine Quiroz-Figueroa, Cecilia Vitali, Donna M. Conlon, John S. Millar, John W. Tobias, Robert C. Bauer, Nicholas J. Hand, Daniel J. Rader