The functional mechanisms and clinical application of read-through drugs.

According to previous reports, nearly one in 10 genetic diseases are caused by nonsense mutations around the world. Nonsense mutations lead to premature transcription terminations in cells, which in turn generate non-functional, truncated proteins. In recent years, read-through drugs are playing increasing prominent roles in the researches related to genetic diseases caused by nonsense mutations. However, due to the fact that the mechanisms lying behind translation termination still remain to be elucidated, the mechanistic research and clinical application of read-through drugs are facing new challenges. This review mainly discusses about the pathogenesis of genetic diseases caused by nonsense mutations, and then introduces the current clinical application of read-through drugs. Finally, we display some problems that remain to be solved and propose some possible coping strategies.

A novel Cx50 (GJA8) p.H277Y mutation associated with autosomal dominant congenital cataract identified with targeted next-generation sequencing.

BACKGROUND: To unravel the molecular genetic background responsible for autosomal dominant congenital pulverulent nuclear cataracts in a four-generation Chinese family. METHODS: Family history data were collected, ophthalmological examinations were performed, and genomic DNA was extracted from peripheral blood of the family members. The candidate genes were captured and sequenced by targeted next-generation sequencing, and the results were confirmed by Sanger sequencing. The structure modelling of the protein was displayed based on Swiss-Model Server, and its possible changes in the secondary structure were predicted using Antheprot 2000 software. The chemical dissimilarity and possible functional impact of an amino acid substitution were performed with Grantham score, PolyPhen-2, and SIFT predictions. Protein distributions were assessed by confocal microscopy. RESULTS: A novel heterozygous c.829C > T transition that led to the substitution of a highly conserved histidine by tyrosine at codon 277 (p.H277Y) in the coding region of connexin50 (Cx50, GJA8) was identified. Bioinformatics analysis showed that the mutation likely altered the secondary structure of the protein by replacing the helix of the COOH-terminal portion with a turn. The mutation was predicted to be moderately conservative by Grantham score and to be deleterious by both PolyPhen-2 and SIFT with consistent results. In addition, when expressed in COS1 cells, the mutation led to protein accumulation and caused changes in Cx 50 protein localization pattern. CONCLUSIONS: This is a novel missense mutation [c.829C > T, (p.H277Y)] identified in exon 2 of Cx50. Our findings expand the spectrum of Cx50 mutations that are associated with autosomal dominant congenital pulverulent nuclear cataract.

DHTKD1 is essential for mitochondrial biogenesis and function maintenance.

Maintaining the functional integrity of mitochondria is crucial for cell function, signal transduction and overall cell activities. Mitochondrial dysfunctions may alter energy metabolism and in many cases are associated with neurological diseases. Recent studies have reported that mutations in dehydrogenase E1 and transketolase domain-containing 1 (DHTKD1), a mitochondrial protein encoding gene, could cause neurological abnormalities. However, the function of DHTKD1 in mitochondria remains unknown. Here, we report a strong correlation of DHTKD1 expression level with ATP production, revealing the fact that DHTKD1 plays a critical role in energy production in mitochondria. Moreover, suppression of DHTKD1 leads to impaired mitochondrial biogenesis and increased reactive oxygen species (ROS), thus leading to retarded cell growth and increased cell apoptosis. These findings demonstrate that DHTKD1 contributes to mitochondrial biogenesis and function maintenance.

The cytoplasmic domain of MUC1 induces hyperplasia in the mammary gland and correlates with nuclear accumulation of ß-catenin.

MUC1 is an oncoprotein that is overexpressed in up to 90% of breast carcinomas. A previous in vitro study by our group demonstrated that the cytoplasmic domain of MUC1 (MUC1-CD), the minimal functional unit of MUC1, contributes to the malignant phenotype in cells by binding directly to ß-catenin and protecting ß-catenin from GSK3ß-induced degradation. To understand the in vivo role of MUC1-CD in breast development, we generated a MUC1-CD transgenic mouse model under the control of the MMTV promoter in a C57BL/6J background, which is more resistant to breast tumor. We show that the expression of MUC1-CD in luminal epithelial cells of the mammary gland induced a hyperplasia phenotype characterized by the development of hyper-branching and extensive lobuloalveoli in transgenic mice. In addition to this hyperplasia, there was a marked increase in cellular proliferation in the mouse mammary gland. We further show that MUC1-CD induces nuclear localization of ß-catenin, which is associated with a significant increase of ß-catenin activity, as shown by the elevated expression of cyclin D1 and c-Myc in MMTV-MUC1-CD mice. Consistent with this finding, we observed that overexpression of MUC1-C is associated with ß-catenin nuclear localization in tumor tissues and increased expression of Cyclin D1 and c-Myc in breast carcinoma specimens. Collectively, our data indicate a critical role for MUC1-CD in the development of mammary gland preneoplasia and tumorigenesis, suggesting MUC1-CD as a potential target for the diagnosis and chemoprevention of human breast cancer.

Germinal Cell Aplasia in Kif18a Mutant Male Mice Due to Impaired Chromosome Congression and Dysregulated BubR1 and CENP-E.

Chromosomal instability during cell division frequently causes cell death or malignant transformation. Orderly chromosome congression at the metaphase plate, a paramount process to vertebrate mitosis and meiosis, is controlled by a number of molecular regulators, including kinesins. Kinesin-8 (Kif18A) functions to control mitotic chromosome alignment at the mid-zone by negative regulation of kinetochore oscillation. Here the authors report that disrupting Kif18a function results in complete sterility in male but not in female mice. Histological examination reveals that Kif18a(-/-) testes exhibit severe developmental impairment of seminiferous tubules. Testis atrophy in Kif18a(-/-) mice is caused by perturbation of microtubule dynamics and spindle pole integrity, leading to chromosome congression defects during mitosis and meiosis. Depletion of KIF18A via RNAi causes mitotic arrest accompanied by unaligned chromosomes and increased microtubule nucleating centers in both GC-1 and HeLa cells. Prolonged depletion of KIF18A causes apoptosis due to perturbed microtubule dynamics. Further studies reveal that KIF18A silencing results in degradation of CENP-E and BubR1, which is accompanied by premature sister chromatid separation. KIF18A physically interacts with BubR1 and CENP-E, and this interaction is modulated during mitosis. Combined, the studies indicate that KIF18A is essential for normal chromosome congression during cell division and that the absence of KIF18A function causes severe defects in microtubule dynamics, spindle integrity, and checkpoint activation, leading to germinal cell aplasia in mice.

Multiple synostoses syndrome is due to a missense mutation in exon 2 of FGF9 gene.

Fibroblast growth factors (FGFs) play diverse roles in several developmental processes. Mutations leading to deregulated FGF signaling can cause human skeletal dysplasias and cancer.(1,2) Here we report a missense mutation (Ser99Asp) in exon 2 of FGF9 in 12 patients with multiple synostoses syndrome (SYNS) in a large Chinese family. In vitro studies demonstrate that FGF9(S99N) is expressed and secreted as efficiently as wild-type FGF9 in transfected cells. However, FGF9(S99N) induces compromised chondrocyte proliferation and differentiation, which is accompanied by enhanced osteogenic differentiation and matrix mineralization of bone marrow-derived mesenchymal stem cells (BMSCs). Biochemical analysis reveals that S99N mutation in FGF9 leads to significantly impaired FGF signaling, as evidenced by diminished activity of Erk1/2 pathway and decreased beta-catenin and c-Myc expression when compared with wild-type FGF9. Importantly, the binding of FGF9(S99N) to its receptor is severely impaired although the dimerization ability of mutant FGF9 itself or with wild-type FGF9 is not detectably affected, providing a basis for the defective FGFR signaling. Collectively, our data demonstrate a previously uncharacterized mutation in FGF9 as one of the causes of SYNS, implicating an important role of FGF9 in normal joint development.

Disruption of palladin leads to defects in definitive erythropoiesis by interfering with erythroblastic island formation in mouse fetal liver.

Palladin was originally found up-regulated with NB4 cell differentiation induced by all-trans retinoic acid. Disruption of palladin results in neural tube closure defects, liver herniation, and embryonic lethality. Here we further report that Palld(-/-) embryos exhibit a significant defect in erythropoiesis characterized by a dramatic reduction in definitive erythrocytes derived from fetal liver but not primitive erythrocytes from yolk sac. The reduction of erythrocytes is accompanied by increased apoptosis of erythroblasts and partial blockage of erythroid differentiation. However, colony-forming assay shows no differences between wild-type (wt) and mutant fetal liver or yolk sac in the number and size of colonies tested. In addition, Palld(-/-) fetal liver cells can reconstitute hematopoiesis in lethally irradiated mice. These data strongly suggest that deficient erythropoiesis in Palld(-/-) fetal liver is mainly due to a compromised erythropoietic microenvironment. As expected, erythroblastic island in Palld(-/-) fetal liver was found disorganized. Palld(-/-) fetal liver cells fail to form erythroblastic island in vitro. Interestingly, wt macrophages can form such units with either wt or mutant erythroblasts, while mutant macrophages lose their ability to bind wt or mutant erythroblasts. These data demonstrate that palladin is crucial for definitive erythropoiesis and erythroblastic island formation and, especially, required for normal function of macrophages in fetal liver.

[Cloning and structural analysis of mouse genomic nucleophosmin gene].

Nucleophosmin (NPM) is an abundant nucleolar phosphoprotein. NPM gene involved chromosomal translocations were found in the patients with anaplastic large cell lymphomas (ALCL), myelodysplastic syndrome (MDS), acute myeloid leukemia (AML) and acute promyelocytic leukemia (APL). To generate NPM gene knockout mice and study its biological function in vivo, we screened the lambda phage genomic library derived from 129S1 mice with mouse NPM cDNA probe. A positive phage clone which contained the full-length NPM genomic DNA was obtained and the insert of 15.3 kb genomic DNA in this clone was sequenced with shotgun method. BLAST analysis showed that the sequence of insert are 99.8% identity to that of NPM gene of C57BL/6 mouse strain. Based on the sequence, bioinformatics analysis on genomic structure of NPM and the transcription factor binding sites in the NPM 5' flanking region were performed.

Disruption of palladin results in neural tube closure defects in mice.

Palladin is a newly identified actin-associated protein which was proposed to be involved in actin cytoskeleton organization and nervous system development. Here, we show that inactivation of palladin leads to embryonic lethality due to severe defects of cranial neural tube closure and herniation of liver and intestine. It was found that palladin(-/-) embryos died around E15.5 and developed cranial neural tube closure defects (NTDs) with 100% penetrance. Whole mount in situ hybridization revealed that expression of palladin in early wild type embryos (E8.5) was specifically restricted in the elevating cranial neural folds where the neural tube closure is initiated. Palladin expression closely mirrors the phenotypic defects observed in palladin(-/-) mutants. While in E 9.5 and E10.5 embryos palladin was ubiquitously expressed. In vitro study revealed that formation of stress fibers in cytoplasm, cell adherent ability to extra-cellular matrix protein fibronectin and cell migration were dramatically disturbed in palladin(-/-) murine embryonic fibroblast cells (MEFs). Our findings suggest that palladin plays important roles in actin stress fiber formation, cell adhesion and migration. We propose that palladin is required for the initiation of neural tube closure and provides an important new candidate that may be implicated in the etiology of human NTDs.

[HUP98-HOXA9 transgenic mice are susceptible to N-ethyl-N-nitrosourea stimulation in leukemogenesis].

OBJECTIVE: In order to investigate the leukemogenic potential of NUP98-HOXA9 fusion gene in vivo. METHODS: Molecular cloning technology was used to construct NUP98-HOXA9 transgenic plasmid and NUP98-HOXA9 transgenic mice were generated. The genotype and phenotype of the NUP98-HOXA9 transgenic mice were analyzed by PCR, RT-PCR and colony-forming assay. The effect of N-ethyl-N-nitrosourea (ENU) stimulation on the transgenic mice was analyzed by peripheral blood count, bone marrow (BM) cells morphology pathological examination. RESULTS: The transgenic expression was detected in 5 independent lines of NUP98-HOXA9 transgenic mice, but no expected phenotypes was found in 2 year follow-up. Upon ENU stimulation, 2 of 10 transgenic mice developed myeloid leukemia, suggesting that NUP98-HOXA9 transgenic mice have increased susceptibility to ENU mutagenesis in leukemogenesis. CONCLUSION: The fusion gene expressed in BM cells of NUP98-HOXA9 transgenic mice. It seems that the expression of the fusion gene is insufficient to trigger leukemogenesis. However, the increased susceptibility to ENU mutagenesis suggests that NUP98-HOXA9 fusion gene might play a potential role in leukemogenesis.

[Development of human myeloid leukemia-like phenotype in NUP98-PMX1 transgenic mice].

OBJECTIVE: In order to investigate the leukemogenic potential of NUP98-PMX1 fusion gene in vivo. METHODS: NUP98-PMX1 transgenic mice were generated, in which the fusion gene was driven by hCG promoter and expressed in myeloid cells at early stage of differentiation. Molecular cloning technology was used to construct NUP98-PMX1 transgenic plasmid. The genotype and phenotype of the NUP98-PMX1 transgenic mice were analyzed by PCR, RT-PCR, peripheral blood count (PBC), bone marrow (BM) cells morphology and pathological examination. RESULTS: NIH3T3 cells transfected with NUP98-PMX1 fusion gene grew faster, formed colonies in soft agar, and developed tumors in 10 inoculated nude mice. Among 8 disordered NUP98-PMX1 transgenic mice, 4 developed myeloid leukemia-like phenotype, including 3 resembling human chronic myeloid leukemia. CONCLUSION: NUP98-PMX1 has oncogenic activity and plays a crucial role in leukemogenesis.