Genetics
Abstract
Exon skipping uses chemically modified antisense oligonucleotides to modulate RNA splicing. Therapeutically, exon skipping can bypass mutations and restore reading frame disruption by generating internally truncated, functional proteins to rescue the loss of native gene expression. Limb-girdle muscular dystrophy type 2C is caused by autosomal recessive mutations in the SGCG gene, which encodes the dystrophin-associated protein γ-sarcoglycan. The most common SGCG mutations disrupt the transcript reading frame abrogating γ-sarcoglycan protein expression. In order to treat most SGCG gene mutations, it is necessary to skip 4 exons in order to restore the SGCG transcript reading frame, creating an internally truncated protein referred to as Mini-Gamma. Using direct reprogramming of human cells with MyoD, myogenic cells were tested with 2 antisense oligonucleotide chemistries, 2’-O-methyl phosphorothioate oligonucleotides and vivo–phosphorodiamidate morpholino oligomers, to induce exon skipping. Treatment with vivo–phosphorodiamidate morpholino oligomers demonstrated efficient skipping of the targeted exons and corrected the mutant reading frame, resulting in the expression of a functional Mini-Gamma protein. Antisense-induced exon skipping of SGCG occurred in normal cells and those with multiple distinct SGCG mutations, including the most common 521ΔT mutation. These findings demonstrate a multiexon-skipping strategy applicable to the majority of limb-girdle muscular dystrophy 2C patients.
Authors
Eugene J. Wyatt, Alexis R. Demonbreun, Ellis Y. Kim, Megan J. Puckelwartz, Andy H. Vo, Lisa M. Dellefave-Castillo, Quan Q. Gao, Mariz Vainzof, Rita C. M. Pavanello, Mayana Zatz, Elizabeth M. McNally
Abstract
Mutations in the gene encoding the protein kinase A (PKA) catalytic subunit α have been found to be responsible for cortisol-producing adenomas (CPAs). In this study, we identified by whole-exome sequencing the somatic mutation p.S54L in the PRKACB gene, encoding the catalytic subunit β (Cβ) of PKA, in a CPA from a patient with severe Cushing syndrome. Bioluminescence resonance energy transfer and surface plasmon resonance assays revealed that the mutation hampers formation of type I holoenzymes and that these holoenzymes were highly sensitive to cAMP. PKA activity, measured both in cell lysates and with recombinant proteins, based on phosphorylation of a synthetic substrate, was higher under basal conditions for the mutant enzyme compared with the WT, while maximal activity was lower. These data suggest that at baseline the PRKACB p.S54L mutant drove the adenoma cells to higher cAMP signaling activity, probably contributing to their autonomous growth. Although the role of PRKACB in tumorigenesis has been suggested, we demonstrated for the first time to our knowledge that a PRKACB mutation can lead to an adrenal tumor. Moreover, this observation describes another mechanism of PKA pathway activation in CPAs and highlights the particular role of residue Ser54 for the function of PKA.
Authors
Stéphanie Espiard, Matthias J. Knape, Kerstin Bathon, Guillaume Assié, Marthe Rizk-Rabin, Simon Faillot, Windy Luscap-Rondof, Daniel Abid, Laurence Guignat, Davide Calebiro, Friedrich W. Herberg, Constantine A. Stratakis, Jérôme Bertherat
Abstract
Heterotopic ossification (HO) is a significant clinical problem with incompletely resolved mechanisms. Here, the secreted metalloproteinases ADAMTS7 and ADAMTS12 are shown to comprise a unique proteoglycan class that protects against a tendency toward HO in mouse hindlimb tendons, menisci, and ligaments. Adamts7 and Adamts12 mRNAs were sparsely expressed in murine forelimbs but strongly coexpressed in hindlimb tendons, skeletal muscle, ligaments, and meniscal fibrocartilage. Adamts7–/– Adamts12–/– mice, but not corresponding single-gene mutants, which demonstrated compensatory upregulation of the intact homolog mRNA, developed progressive HO in these tissues after 4 months of age. Adamts7–/– Adamts12–/– tendons had abnormal collagen fibrils, accompanied by reduced levels of the small leucine-rich proteoglycans (SLRPs) biglycan, fibromodulin, and decorin, which regulate collagen fibrillogenesis. Bgn–/0 Fmod–/– mice are known to have a strikingly similar hindlimb HO to that of Adamts7–/– Adamts12–/– mice, implicating fibromodulin and biglycan reduction as a likely mechanism underlying HO in Adamts7–/– Adamts12–/– mice. Interestingly, degenerated human biceps tendons had reduced ADAMTS7 mRNA compared with healthy biceps tendons, which expressed both ADAMTS7 and ADAMTS12. These results suggest that ADAMTS7 and ADAMTS12 drive an innate pathway protective against hindlimb HO in mice and may be essential for human tendon health.
Authors
Timothy J. Mead, Daniel R. McCulloch, Jason C. Ho, Yaoyao Du, Sheila M. Adams, David E. Birk, Suneel S. Apte
Abstract
Heterozygous chromosomal inversions suppress recombination. Therefore, they may potentially influence recombination-associated phenotypes of human diseases, but no studies have verified this hypothesis. Here, we describe a 35-year-old man with severe congenital ichthyosis. Mutation analysis revealed a heterozygous splice-site mutation, c.1374-2A>G (p.Ser458Argfs*120), in KRT10 on 17q21.2. This mutation was previously reported in patients with ichthyosis with confetti type I (IWC-I), a prominent skin disease characterized by the frequent occurrence of recombination-induced reversion of pathogenic mutations. Intriguingly, the number of revertant skin areas in this patient is considerably reduced compared with typical IWC-I cases. G-banded karyotyping revealed that the patient harbors a heterozygous nonpathogenic inversion, inv(17)(p13q12), whose long-arm breakpoint was subsequently refined to chromosomal positions (chr17: 36,544,407–36,639,830) via FISH. Collectively, the only chance of revertant mosaicism through somatic recombination appears to involve recombination between the KRT10 mutation and the inversion breakpoint. Indeed, in the examined revertant spot, the KRT10 mutation was diminished by somatic recombination starting from chromosomal positions (chr17: 36,915,505–37,060,285) on 17q12. This study provides the first evidence to our knowledge implicating chromosomal inversions as a potential modifier of clinical phenotypes. Furthermore, the reduced occurrence of revertant spots in the recombination-suppressed patient suggests that somatic recombination is the main mechanism of revertant mosaicism in IWC-I.
Authors
Toshifumi Nomura, Shotaro Suzuki, Toshinari Miyauchi, Masae Takeda, Satoru Shinkuma, Yasuyuki Fujita, Wataru Nishie, Masashi Akiyama, Hiroshi Shimizu
Abstract
BACKGROUND. HELLP (hemolysis, elevated liver enzymes, and low platelets) syndrome is a severe variant of hypertensive disorders of pregnancy affecting approximately 1% of all pregnancies, and has significant maternal and fetal morbidity. Previously, we showed that upregulation of the alternative pathway of complement (APC) plays a role in HELLP syndrome. We hypothesize that HELLP syndrome follows a 2-hit disease model similar to atypical hemolytic uremic syndrome (aHUS), requiring both genetic susceptibility and an environmental risk factor. Our objective was to perform a comparative analysis of the frequency of APC activation and germline mutations in affected women and to create a predictive model for identifying HELLP syndrome. METHODS. Pregnant women with HELLP syndrome, and healthy controls after 23 weeks of gestation were recruited, along with aHUS and thrombotic thrombocytopenic purpura participants. We performed a functional assay, the mHam, and targeted genetic sequencing in all groups. RESULTS. Significantly more participants with rare germline mutations in APC genes were present in the HELLP cohort compared with controls (46% versus 8%, P = 0.01). In addition, significantly more HELLP participants were positive for the mHam when compared with controls (62% versus 16%, P = 0.009). Testing positive for both a germline mutation and the mHam was highly predictive for the diagnosis of HELLP syndrome. CONCLUSION. HELLP syndrome is characterized by both activation of the APC and frequent germline mutations in APC genes. Similar to aHUS, treatment via complement inhibition to mitigate maternal and fetal morbidity and mortality may be possible. FUNDING. National Heart Lung and Blood Institute grants T32HL007525 and R01HL133113.
Authors
Arthur J. Vaught, Evan M. Braunstein, Jagar Jasem, Xuan Yuan, Igor Makhlin, Solange Eloundou, Andrea C. Baines, Samuel A. Merrill, Shruti Chaturvedi, Karin Blakemore, C. John Sperati, Robert A. Brodsky
Abstract
Autosomal dominant polycystic kidney disease (ADPKD) can be caused by mutations in the PKD1 or PKD2 genes. The PKD1 gene product is a Wnt cell-surface receptor. We previously showed that a lack of the PKD2 gene product, PC2, increases β-catenin signaling in mouse embryonic fibroblasts, kidney renal epithelia, and isolated renal collecting duct cells. However, it remains unclear whether β-catenin signaling plays a role in polycystic kidney disease phenotypes or if a Wnt inhibitor can halt cyst formation in ADPKD disease models. Here, using genetic and pharmacologic approaches, we demonstrated that the elevated β-catenin signaling caused by PC2 deficiency contributes significantly to disease phenotypes in a mouse ortholog of human ADPKD. Pharmacologically inhibiting β-catenin stability or the production of mature Wnt protein, or genetically reducing the expression of Ctnnb1 (which encodes β-catenin), suppressed the formation of renal cysts, improved renal function, and extended survival in ADPKD mice. Our study clearly demonstrates the importance of β-catenin signaling in disease phenotypes associated with Pkd2 mutation. It also describes the effects of two Wnt inhibitors, XAV939 and LGK974, on various Wnt signaling targets as a potential therapeutic modality for ADPKD, for which there is currently no effective therapy.
Authors
Ao Li, Yuchen Xu, Song Fan, Jialin Meng, Xufeng Shen, Qian Xiao, Yuan Li, Li Zhang, Xiansheng Zhang, Guanqing Wu, Chaozhao Liang, Dianqing Wu
Abstract
Allogeneic hematopoietic cell transplantation (alloHCT) is a potentially curative treatment for myelodysplastic syndromes (MDS), but patients who relapse after transplant have poor outcomes. In order to understand the contribution of tumor clonal evolution to disease progression,we applied exome and error-corrected targeted sequencing coupled with copy number analysis to comprehensively define changes in the clonal architecture of MDS in response to therapy using 51 serially acquired tumor samples from 9 patients who progressed after an alloHCT. We show that small subclones before alloHCT can drive progression after alloHCT. Notably, at least one subclone expanded or emerged at progression in all patients. Newly acquired structural variants (SVs) were present in an emergent/expanding subclone in 8 of 9 patients at progression, implicating the acquisition of SVs as important late subclonal progression events. In addition, pretransplant therapy with azacitidine likely influenced the mutation spectrum and evolution of emergent subclones after alloHCT. Although subclone evolution is common, founding clone mutations are always present at progression and could be detected in the bone marrow as early as 30 and/or 100 days after alloHCT in 6 of 8 (75%) patients, often prior to clinical progression. In conclusion, MDS progression after alloHCT is characterized by subclonal expansion and evolution, which can be influenced by pretransplant therapy.
Authors
Meagan A. Jacoby, Eric J. Duncavage, Gue Su Chang, Christopher A. Miller, Jin Shao, Kevin Elliott, Joshua Robinson, Robert S. Fulton, Catrina C. Fronick, Michelle O’Laughlin, Sharon E. Heath, Iskra Pusic, John S. Welch, Daniel C. Link, John F. DiPersio, Peter Westervelt, Timothy J. Ley, Timothy A. Graubert, Matthew J. Walter
Abstract
Programmed cell death protein 1 (PD-1) inhibitors have efficacy in treating squamous cell carcinoma of the head and neck (SCCHN), but objective response rates are low. PD-1 ligand (PD-L1) expression alone is not considered a robust predictor of response and additional biomarkers are needed. This 3-year observational cohort followed 126 SCCHN patients treated with anti–PD-1/L1 therapy. Prior to treatment, 81 (64%) had targeted massively parallel tumor sequencing. Of these, 42 (52%) underwent fluorescence-activated cell sorting and PD-L1 immunohistochemistry for tumor immunoprofiling. Six (5%) complete responses (CRs) and 11 (9%) partial responses (PRs) were observed. Those treated with prior chemotherapy (98, 78%) versus only surgery and/or radiation had longer overall survival (OS) (10 vs. 3 months, P = 0.02). Smokers had a higher total mutational burden (TMB) (P = 0.01). Virus-positive patients had a lower TMB (P < 0.01) and improved OS (P = 0.02). Among virus-negative responders, NOTCH1 and SMARCA4 were more frequently mutated and frameshift events in tumor suppressor genes occurred more frequently (P = 0.03). Higher TMB and CD8+ T cell infiltrates predicted anti–PD-1/L1 benefit (P < 0.01, P < 0.01, respectively) among virus-negative tumors. TIM-3/LAG-3 coexpression with PD-1 was higher on T cells among nonresponders (P = 0.03 and 0.02, respectively). Somatic frameshift events in tumor suppressor genes and higher TMB among virus-negative SCCHN tumors predict anti–PD-1/L1 response.
Authors
Glenn J. Hanna, Patrick Lizotte, Megan Cavanaugh, Frank C. Kuo, Priyanka Shivdasani, Alexander Frieden, Nicole G. Chau, Jonathan D. Schoenfeld, Jochen H. Lorch, Ravindra Uppaluri, Laura E. MacConaill, Robert I. Haddad
Abstract
Incomplete penetrance of congenital heart defects (CHDs) was observed in a mouse model. We hypothesized that the contribution of a major genetic locus modulates the manifestation of the CHDs. After genome-wide linkage mapping, fine mapping, and high-throughput targeted sequencing, a recessive frameshift mutation of the heterogeneous nuclear ribonucleoprotein A1 (Hnrnpa1) gene was confirmed (Hnrnpa1ct). Hnrnpa1 was expressed in both the first heart field (FHF) and second heart field (SHF) at the cardiac crescent stage but was only maintained in SHF progenitors after heart tube formation. Hnrnpa1ct/ct homozygous mutants displayed complete CHD penetrance, including truncated and incomplete looped heart tube at E9.5, ventricular septal defect (VSD) and persistent truncus arteriosus (PTA) at E13.5, and VSD and double outlet right ventricle at P0. Impaired development of the dorsal mesocardium and sinoatrial node progenitors was also observed. Loss of Hnrnpa1 expression leads to dysregulation of cardiac transcription networks and multiple signaling pathways, including BMP, FGF, and Notch in the SHF. Finally, two rare heterozygous mutations of HNRNPA1 were detected in human CHDs. These findings suggest a role of Hnrnpa1 in embryonic heart development in mice and humans.
Authors
Zhe Yu, Paul L.F. Tang, Jing Wang, Suying Bao, Joseph T. Shieh, Alan W.L. Leung, Zhao Zhang, Fei Gao, Sandra Y.Y. Wong, Andy L.C. Hui, Yuan Gao, Nelson Dung, Zhi-Gang Zhang, Yanhui Fan, Xueya Zhou, Yalun Zhang, Dana S.M. Wong, Pak C. Sham, Abid Azhar, Pui-Yan Kwok, Patrick P.L. Tam, Qizhou Lian, Kathryn S.E. Cheah, Binbin Wang, You-Qiang Song
Abstract
Heterogeneity within and among tumors in a metastatic cancer patient is a well-established phenomenon that may confound treatment and accurate prognosis. Here, we used whole-exome sequencing to survey metastatic breast cancer tumors from 5 patients in a rapid autopsy program to construct the origin and genetic development of metastases. Metastases were obtained from 5 breast cancer patients using a rapid autopsy protocol and subjected to whole-exome sequencing. Metastases were evaluated for sharing of somatic mutations, correlation of copy number variation and loss of heterozygosity, and genetic similarity scores. Pathological features of the patients’ disease were assessed by immunohistochemical analyses. Our data support a monoclonal origin of metastasis in 3 cases, but in 2 cases, metastases arose from at least 2 distinct subclones in the primary tumor. In the latter 2 cases, the primary tumor presented with mixed histologic and pathologic features, suggesting early divergent evolution within the primary tumor with maintenance of metastatic capability in multiple lineages. We used genetic and histopathological evidence to demonstrate that metastases can be derived from a single or multiple independent clones within a primary tumor. This underscores the complexity of breast cancer clonal evolution and has implications for how best to determine and implement therapies for early- and late-stage disease.
Authors
Bracha Erlanger Avigdor, Ashley Cimino-Mathews, Angelo M. DeMarzo, Jessica L. Hicks, James Shin, Saraswati Sukumar, John Fetting, Pedram Argani, Ben H. Park, Sarah J. Wheelan
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