Nucleolar disruption, activation of P53 and premature senescence in POLR3A-mutated Wiedemann-Rautenstrauch syndrome fibroblasts

Clinical phenotype and genetic function analysis of a family with hypomyelinating leukodystrophy-7 caused by POLR3A mutation

Hypomyelinating leukodystrophy (HLD) is a rare genetic heterogeneous disease that can affect myelin development in the central nervous system. This study aims to analyze the clinical phenotype and genetic function of a family with HLD-7 caused by POLR3A mutation. The proband (IV6) in this family mainly showed progressive cognitive decline, dentin dysplasia, and hypogonadotropic hypogonadism. Her three old brothers (IV1, IV2, and IV4) also had different degrees of ataxia, dystonia, or dysarthria besides the aforementioned manifestations. Their brain magnetic resonance imaging showed bilateral periventricular white matter atrophy, brain atrophy, and corpus callosum atrophy and thinning. The proband and her two living brothers (IV2 and IV4) were detected to carry a homozygous mutation of the POLR3A (NM_007055.4) gene c. 2300G > T (p.Cys767Phe), and her consanguineous married parents (III1 and III2) were p.Cys767Phe heterozygous carriers. In the constructed POLR3A wild-type and p.Cys767Phe mutant cells, it was seen that overexpression of wild-type POLR3A protein significantly enhanced Pol III transcription of 5S rRNA and tRNA Leu-CAA. However, although the mutant POLR3A protein overexpression was increased compared to the wild-type protein overexpression, it did not show the expected further enhancement of Pol III function. On the contrary, Pol III transcription function was frustrated (POLR3A, BC200, and tRNA Leu-CAA expression decreased), and MBP and 18S rRNA expressions were decreased. This study indicates that the POLR3A p.Cys767Phe variant caused increased expression of mutated POLR3A protein and abnormal expression of Pol III transcripts, and the mutant POLR3A protein function was abnormal.

A POLR3B-variant reveals a Pol III transcriptome response dependent on La protein/SSB

RNA polymerase III (Pol III, POLR3) synthesizes tRNAs and other small non-coding RNAs. Human POLR3 pathogenic variants cause a range of developmental disorders, recapitulated in part by mouse models, yet some aspects of POLR3 deficiency have not been explored. We characterized a human POLR3B:c.1625A>G;p.(Asn542Ser) disease variant that was found to cause mis-splicing of POLR3B. Genome-edited POLR3B1625A>G HEK293 cells acquired the mis-splicing with decreases in multiple POLR3 subunits and TFIIIB, although display auto-upregulation of the Pol III termination-reinitiation subunit POLR3E. La protein was increased relative to its abundant pre-tRNA ligands which bind via their U(n)U-3'-termini. Assays for cellular transcription revealed greater deficiencies for tRNA genes bearing terminators comprised of 4Ts than of ≥5Ts. La-knockdown decreased Pol III ncRNA expression unlinked to RNA stability. Consistent with these effects, small-RNAseq showed that POLR3B1625A>G and patient fibroblasts express more tRNA fragments (tRFs) derived from pre-tRNA 3'-trailers (tRF-1) than from mature-tRFs, and higher levels of multiple miRNAs, relative to control cells. The data indicate that decreased levels of Pol III transcripts can lead to functional excess of La protein which reshapes small ncRNA profiles revealing new depth in the Pol III system. Finally, patient cell RNA analysis uncovered a strategy for tRF-1/tRF-3 as POLR3-deficiency biomarkers.

[Wiedemann-Rautenstrauch syndrome. The first description of a clinical case in the Russian Federation]

Wiedemann-Rautenstrauch syndrome (neonatal progeroid syndrome) is an ultra-orphan disease from the group of premature aging syndromes with an autosomal recessive type of inheritance associated with mutations in the POLR3A, POLR3B, and POLR3GL genes encoding RNA polymerase III. The incidence of the disease is currently unknown. We present the first clinical description in Russian Federation of a patient 7 years 6 months old with Wiedemann-Rautenstrauch syndrome (compound heterozygous mutations in POLR3A gene) with progeroid features, adentia, growth retardation (height SDS -3,41, height velocity SDS -2,47), underweight (BMI SDS -6,20), and generalized lipodystrophy. The article presents the observation of the patient for 1.5 years, the world experience of dynamic follow-up of patients with neonatal progeroid syndrome, differential diagnosis, as well as recommendations for the management of patients with this syndrome. Given the lack of specific treatment to date, patients are observed by a multidisciplinary team of physicians.

RNA Polymerases I and III in development and disease

Ribosomes are macromolecular machines that are globally required for the translation of all proteins in all cells. Ribosome biogenesis, which is essential for cell growth, proliferation and survival, commences with transcription of a variety of RNAs by RNA Polymerases I and III. RNA Polymerase I (Pol I) transcribes ribosomal RNA (rRNA), while RNA Polymerase III (Pol III) transcribes 5S ribosomal RNA and transfer RNAs (tRNA) in addition to a wide variety of small non-coding RNAs. Interestingly, despite their global importance, disruptions in Pol I and Pol III function result in tissue-specific developmental disorders, with craniofacial anomalies and leukodystrophy/neurodegenerative disease being among the most prevalent. Furthermore, pathogenic variants in genes encoding subunits shared between Pol I and Pol III give rise to distinct syndromes depending on whether Pol I or Pol III function is disrupted. In this review, we discuss the global roles of Pol I and III transcription, the consequences of disruptions in Pol I and III transcription, disorders arising from pathogenic variants in Pol I and Pol III subunits, and mechanisms underpinning their tissue-specific phenotypes.

Tuning between Nuclear Organization and Functionality in Health and Disease

The organization of eukaryotic genome in the nucleus, a double-membraned organelle separated from the cytoplasm, is highly complex and dynamic. The functional architecture of the nucleus is confined by the layers of internal and cytoplasmic elements, including chromatin organization, nuclear envelope associated proteome and transport, nuclear-cytoskeletal contacts, and the mechano-regulatory signaling cascades. The size and morphology of the nucleus could impose a significant impact on nuclear mechanics, chromatin organization, gene expression, cell functionality and disease development. The maintenance of nuclear organization during genetic or physical perturbation is crucial for the viability and lifespan of the cell. Abnormal nuclear envelope morphologies, such as invagination and blebbing, have functional implications in several human disorders, including cancer, accelerated aging, thyroid disorders, and different types of neuro-muscular diseases. Despite the evident interplay between nuclear structure and nuclear function, our knowledge about the underlying molecular mechanisms for regulation of nuclear morphology and cell functionality during health and illness is rather poor. This review highlights the essential nuclear, cellular, and extracellular components that govern the organization of nuclei and functional consequences associated with nuclear morphometric aberrations. Finally, we discuss the recent developments with diagnostic and therapeutic implications targeting nuclear morphology in health and disease.

Lipodystrophy-associated progeroid syndromes

With the exception of HIV-associated lipodystrophy, lipodystrophy syndromes are rare conditions characterized by a lack of adipose tissue, which is not generally recovered. As a consequence, an ectopic deposition of lipids frequently occurs, which usually leads to insulin resistance, atherogenic dyslipidemia, and hepatic steatosis. These disorders include certain accelerated aging syndromes or progeroid syndromes. Even though each of them has unique clinical features, most show common clinical characteristics that affect growth, skin and appendages, adipose tissue, muscle, and bone and, in some of them, life expectancy is reduced. Although the molecular bases of these Mendelian disorders are very diverse and not well known, genomic instability is frequent as a consequence of impairment of nuclear organization, chromatin structure, and DNA repair, as well as epigenetic dysregulation and mitochondrial dysfunction. In this review, the main clinical features of the lipodystrophy-associated progeroid syndromes will be described along with their causes and pathogenic mechanisms, and an attempt will be made to identify which of López-Otín's hallmarks of aging are present.

RNA Polymerase III Subunit Mutations in Genetic Diseases

RNA polymerase (Pol) III transcribes small untranslated RNAs such as 5S ribosomal RNA, transfer RNAs, and U6 small nuclear RNA. Because of the functions of these RNAs, Pol III transcription is best known for its essential contribution to RNA maturation and translation. Surprisingly, it was discovered in the last decade that various inherited mutations in genes encoding nine distinct subunits of Pol III cause tissue-specific diseases rather than a general failure of all vital functions. Mutations in the POLR3A, POLR3C, POLR3E and POLR3F subunits are associated with susceptibility to varicella zoster virus-induced encephalitis and pneumonitis. In addition, an ever-increasing number of distinct mutations in the POLR3A, POLR3B, POLR1C and POLR3K subunits cause a spectrum of neurodegenerative diseases, which includes most notably hypomyelinating leukodystrophy. Furthermore, other rare diseases are also associated with mutations in genes encoding subunits of Pol III (POLR3H, POLR3GL) and the BRF1 component of the TFIIIB transcription initiation factor. Although the causal relationship between these mutations and disease development is widely accepted, the exact molecular mechanisms underlying disease pathogenesis remain enigmatic. Here, we review the current knowledge on the functional impact of specific mutations, possible Pol III-related disease-causing mechanisms, and animal models that may help to better understand the links between Pol III mutations and disease.

Molecular predictors of the outcome of paclitaxel plus carboplatin neoadjuvant therapy in high-grade serous ovarian cancer patients

BACKGROUND

Patients with advanced high-grade serous ovarian cancer (HGSOC) are usually treated with paclitaxel and carboplatin; however, predictive markers for this drug combination are unknown.

METHODS

Tumor samples from 71 consecutive HGSOC patients, who received neoadjuvant chemotherapy with paclitaxel and carboplatin, were subjected to molecular analysis.

RESULTS

BRCA1/2 germline mutation carriers (n = 22) had longer treatment-free interval (TFI) than non-carriers (n = 49) (9.5 months vs. 3.8 months; P = 0.007). Fifty-one HGSOCs had sufficient quality of tumor DNA for the next-generation sequencing (NGS) analysis by the SeqCap EZ CNV/LOH Backbone Design panel. All 13 tumors obtained from BRCA1/2 germline mutation carriers and 12 sporadic HGSOCs showed a high number of evenly spread chromosomal breaks, which was defined as a BRCAness phenotype; median TFI for this combined group approached 9.5 months. The remaining 26 HGSOCs had similarly high global LOH score (above 20%); however, in contrast to BRCAness tumors, LOH involved large chromosomal segments; these patients had significantly lower TFI (3.7 months; P = 0.006). All patients with CCNE1 amplification (n = 7), TP53 R175H substitution (n = 6), and RB1 mutation (n = 4) had poor response to paclitaxel plus carboplatin.

CONCLUSION

This study describes a cost-efficient method of detecting the BRCAness phenotype, which is compatible with the laboratory-scale NGS equipment. Some molecular predictors allow the identification of potential non-responders to paclitaxel plus carboplatin, who may need to be considered for other treatment options.