Splicing Factor PQBP1 Curtails BAX Expression to Promote Ovarian Cancer Progression

Splicing factor polyglutamine binding protein-1 (PQBP1) is abundantly expressed in the central nervous system during development, and mutations in the gene cause intellectual disability. However, the roles of PQBP1 in cancer progression remain largely unknown. Here, it is shown that PQBP1 overexpression promotes tumor progression and indicates worse prognosis in ovarian cancer. Integrative analysis of spyCLIP-seq and RNA-seq data reveals that PQBP1 preferentially binds to exon regions and modulates exon skipping. Mechanistically, it is shown that PQBP1 regulates the splicing of genes related to the apoptotic signaling pathway, including BAX. PQBP1 promotes BAX exon 2 skipping to generate a truncated isoform that undergoes degradation by nonsense-mediated mRNA decay, thus making cancer cells resistant to apoptosis. In contrast, PQBP1 depletion or splice-switching antisense oligonucleotides promote exon 2 inclusion and thus increase BAX expression, leading to inhibition of tumor growth. Together, the results demonstrate an oncogenic role of PQBP1 in ovarian cancer and suggest that targeting the aberrant splicing mediated by PQBP1 has therapeutic potential in cancer treatment.

PQBP1 regulates the cellular inflammation induced by avian reovirus and interacts with the viral p17 protein

Avian reovirus (ARV) can commonly infect a flock and cause immunosuppressive diseases in poultry. The nonstructural protein p17 is involved in viral replication, and significant progress has been made in showing its ability to regulate cellular signaling pathways. In our previous study, to further investigate the effect of ARV p17 protein on viral replication, the host protein polyglu-tamine binding protein 1 (PQBP1) was identified to interact with p17 by a yeast two-hybrid system. In the current study, the interaction between PQBP1 and p17 protein was further confirmed by laser confocal microscopy and coimmunoprecipitation assays. In addition, the N-terminal WWD of PQBP1 was found to mediate the process of binding to the p17 protein. Interestingly, we found that ARV infection significantly inhibited PQBP1 expression. While the quantity of ARV replication was largely influenced by PQBP1, PQBP1 overexpression decreased ARV replication. In contrast, upon PQBP1 knockdown, the quantity of ARV was notably increased. ARV infection and p17 protein expression were both proven to induce PQBP1 to mediate cellular inflammation. In the current study, we revealed through qRT‒PCR, ELISA and Western blotting methods that PQBP1 plays a positive role in ARV-induced inflammation. Furthermore, the mechanism of this process was shown to involve the NFκB-dependent transcription of inflammatory genes. In addition, PQBP1 was shown to regulate the phosphorylation of p65 protein. In conclusion, this research provides clues to elucidating the function of the p17 protein and the pathogenic mechanism of ARV, especially the cause of the inflammatory response. It also provides new ideas for the study of therapeutic targets of ARV.

PQBP1 regulates striatum development through balancing striatal progenitor proliferation and differentiation

The balance between cell proliferation and differentiation is essential for maintaining the neural progenitor pool and brain development. Although the mechanisms underlying cell proliferation and differentiation at the transcriptional level have been studied intensively, post-transcriptional regulation of cell proliferation and differentiation remains largely unclear. Here, we show that deletion of the alternative splicing regulator PQBP1 in striatal progenitors results in defective striatal development due to impaired neurogenesis of spiny projection neurons (SPNs). Pqbp1-deficient striatal progenitors exhibit declined proliferation and increased differentiation, resulting in a reduced striatal progenitor pool. We further reveal that PQBP1 associates with components in splicing machinery. The alternative splicing profiles identify that PQBP1 promotes the exon 9 inclusion of Numb, a variant that mediates progenitor proliferation. These findings identify PQBP1 as a regulator in balancing striatal progenitor proliferation and differentiation and provide alternative insights into the pathogenic mechanisms underlying Renpenning syndrome.

The role of PQBP1 in neural development and function

Mutations in the polyglutamine tract-binding protein 1 (PQBP1) gene are associated with Renpenning syndrome, which is characterized by microcephaly, intellectual deficiency, short stature, small testes, and distinct facial dysmorphism. Studies using different models have revealed that PQBP1 plays essential roles in neural development and function. In this mini-review, we summarize recent findings relating to the roles of PQBP1 in these processes, including in the regulation of neural progenitor proliferation, neural projection, synaptic growth, neuronal survival, and cognitive function via mRNA transcription and splicing-dependent or -independent processes. The novel findings provide insights into the mechanisms underlying the pathogenesis of Renpenning syndrome and may advance drug discovery and treatment for this condition.

Recognition of HIV-1 capsid by PQBP1 licenses an innate immune sensing of nascent HIV-1 DNA

We have previously described polyglutamine-binding protein 1 (PQBP1) as an adapter required for the cyclic GMP-AMP synthase (cGAS)-mediated innate response to the human immunodeficiency virus 1 (HIV-1) and other lentiviruses. Cytoplasmic HIV-1 DNA is a transient and low-abundance pathogen-associated molecular pattern (PAMP), and the mechanism for its detection and verification is not fully understood. Here, we show a two-factor authentication strategy by the innate surveillance machinery to selectively respond to the low concentration of HIV-1 DNA, while distinguishing these species from extranuclear DNA molecules. We find that, upon HIV-1 infection, PQBP1 decorates the intact viral capsid, and this serves as a primary verification step for the viral nucleic acid cargo. As reverse transcription and capsid disassembly initiate, cGAS is recruited to the capsid in a PQBP1-dependent manner. This positions cGAS at the site of PAMP generation and sanctions its response to a low-abundance DNA PAMP.

PQBP1: The Key to Intellectual Disability, Neurodegenerative Diseases, and Innate Immunity

The idea that a common pathology underlies various neurodegenerative diseases and dementias has attracted considerable attention in the basic and medical sciences. Polyglutamine binding protein-1 (PQBP1) was identified in 1998 after a molecule was predicted to bind to polyglutamine tract amino acid sequences, which are associated with a family of neurodegenerative disorders called polyglutamine diseases. Hereditary gene mutations of PQBP1 cause intellectual disability, whereas acquired loss of function of PQBP1 contributes to dementia pathology. PQBP1 functions in innate immune cells as an intracellular receptor that recognizes pathogens and neurodegenerative proteins. It is an intrinsically disordered protein that generates intracellular foci, similar to other neurodegenerative disease proteins such as TDP43, FUS, and hnRNPs. The knowledge accumulated over more than 20 years has given rise to a new concept that shifts in the equilibrium between physiological and pathological processes have their basis in the dysregulation of common protein structure-linked molecular mechanisms.

PQBP1 promotes translational elongation and regulates hippocampal mGluR-LTD by suppressing eEF2 phosphorylation

Eukaryotic elongation factor 2 (eEF2) mediates translocation of peptidyl-tRNA from the ribosomal A site to the P site to promote translational elongation. Its phosphorylation on Thr56 by its single known kinase eEF2K inactivates it and inhibits translational elongation. Extensive studies have revealed that different signal cascades modulate eEF2K activity, but whether additional factors regulate phosphorylation of eEF2 remains unclear. Here, we find that the X chromosome-linked intellectual disability protein polyglutamine-binding protein 1 (PQBP1) specifically binds to non-phosphorylated eEF2 and suppresses eEF2K-mediated phosphorylation at Thr56. Loss of PQBP1 significantly reduces general protein synthesis by suppressing translational elongation. Moreover, we show that PQBP1 regulates hippocampal metabotropic glutamate receptor-dependent long-term depression (mGluR-LTD) and mGluR-LTD-associated behaviors by suppressing eEF2K-mediated phosphorylation. Our results identify PQBP1 as a novel regulator in translational elongation and mGluR-LTD, and this newly revealed regulator in the eEF2K/eEF2 pathway is also an excellent therapeutic target for various disease conditions, such as neural diseases, virus infection, and cancer.

Renpenning Syndrome in a Turkish Patient: de novo Variant c.607C>T in PACS1 and Hypogammaglobulinemia Phenotype

Renpenning syndrome is an X-linked intellectual disability syndrome caused by mutations in the human polyglutamine binding protein 1 (PQBP1) gene characterized by intellectual disability (ID), microcephaly, and dysmorphic facial features. We report a Turkish child with a novel pathogenic variant in PQBP1 and a likely pathogenic variant in the PACS1 gene presenting with growth restriction, microcephaly, ID, micropenis, bilateral iris coloboma, and hypogammaglobulinemia. Cytogenetic investigations, including a high-resolution-banded karyotype, were normal. Clinical exome sequencing was performed. We found the novel PQBP1 variant, c.640C>T; p.(Arg214Trp), and the known PACS1 variant, c.607C>T; p.(Arg203Trp), in the proband. The patient's hypogammaglobulinemia did not respond to treatment. This condition was detected for the first time in a patient with Renpenning syndrome.

The Renpenning syndrome-associated protein PQBP1 facilitates the nuclear import of splicing factor TXNL4A through the karyopherin β2 receptor

Renpenning syndrome belongs to a group of X-linked intellectual disability disorders. The Renpenning syndrome-associated protein PQBP1 (polyglutamine-binding protein 1) is intrinsically disordered, associates with several splicing factors, and is involved in pre-mRNA splicing. PQBP1 uses its C-terminal YxxPxxVL motif for binding to the splicing factor TXNL4A (thioredoxin like 4A), but the biological function of this interaction has yet to be elucidated. In this study, using recombinant protein expression, in vitro binding assays, and immunofluorescence microscopy in HeLa cells, we found that a recently reported X-linked intellectual disability-associated missense mutation, resulting in the PQBP1-P244L variant, disrupts the interaction with TXNL4A. We further show that this interaction is critical for the subcellular location of TXNL4A. In combination with other PQBP1 variants lacking a functional nuclear localization signal required for recognition by the nuclear import receptor karyopherin β2, we demonstrate that PQBP1 facilitates the nuclear import of TXNL4A via a piggyback mechanism. These findings expand our understanding of the molecular basis of the PQBP1-TXNL4A interaction and of the etiology and pathogenesis of Renpenning syndrome and related disorders.

Renpenning syndrome in an Indian patient

Renpenning syndrome is one of the well-characterized causes of X-linked intellectual disability and is associated with microcephaly and various visceral malformations. Face is considered characteristic but the dysmorphism is subtle. Here we report an Indian adult with a very lean habitus, progressive atrophy of the upper back muscles, microcephaly, loss of cervical lordosis, and upper thoracic scoliosis. Using whole-exome sequencing, a hemizygous deletion was identified in PQBP1 that leads to a frameshift and premature termination of translation. The loss of normal curvatures of cervical and upper thoracic spine due to muscular atrophy is a characteristic feature, though it may be age dependent.

Renpenning syndrome in a female

Renpenning syndrome (OMIM: 309500) is a rare X-linked disorder that causes intellectual disability, microcephaly, short stature, a variety of eye anomalies, and characteristic craniofacial features. This condition results from pathogenic variation of PQBP1, a polyglutamine-binding protein involved in transcription and pre-mRNA splicing. Renpenning syndrome has only been reported in affected males. Carrier females do not usually have clinical features, and in reported families with Renpenning syndrome, most female carriers exhibit favorable skewing of X-chromosome inactivation. We describe a female with syndromic features typical of Renpenning syndrome. She was identified by exome sequencing to have a de novo heterozygous c.459_462delAGAG mutation in PQBP1 (Xp11.23), affecting the AG hexamer in exon 4, which is the most common causative mutation in this syndrome. Streaky hypopigmentation of the skin was observed, supporting a hypothesized presence of an actively expressed, PQBP1 mutation-bearing X-chromosome in some cells. X-inactivation studies on peripheral blood cells demonstrated complete skewing in both the proband and her mother with preferential inactivation of the maternal X chromosome in the child. We demonstrated expression of the PQBP1 mutant transcript in leukocytes of the affected girl. Therefore, it is highly likely that the PQBP1 mutation arose from the paternal X chromosome.

High Expression of PQBP1 and Low Expression of PCK2 are Associated with Metastasis and Recurrence of Osteosarcoma and Unfavorable Survival Outcomes of the Patients

Osteosarcoma (OS) is the most common primary bone malignancy, predominately affecting children and adolescents. Due to the introduction of chemotherapy, the 5-year survival rate of OS patients has dramatically improved to 60-70%. Unfortunately, OS patients with recurrence or metastatic disease have less than a 20% chance of long-term survival, despite aggressive therapies. In this study, we aimed to identify gene expression patterns associated with metastasis and recurrence in order to identify potential biomarkers with prognostic power. We found that high expression of polyglutamine tract-binding protein 1 (PQBP1) and low expression of phosphoenolpyruvate carboxykinase 2 (PCK2) were related to a high probability of recurrence and metastasis in OS patients and also predicted shorter recurrence-free survival (RFS) and metastasis-free survival (MFS) after adjustment for other clinical variables. Prediction models based on the combination of PQBP1 and PCK2 expression had good and robust predictive power for recurrence and metastasis. A PQBP1 and PCK2-centered protein interaction network was built, and the hypothetical regulatory path between them was identified and termed the PQBP1-SF3A2-UBA52-PCK2 axis. Gene enrichment analysis indicated that aberrations of metabolism might play an important role in recurrence and metastasis in OS patients. Accordingly, PQBP1 and PCK2 are crucial for recurrence and metastasis in OS, and these findings provide a molecular basis for the exploitation of diagnostic and therapeutic strategies for overcoming recurrence and metastasis in OS.

Phenotypic and molecular insights into PQBP1-related intellectual disability

We report two discordant clinical and imaging features in four male patients from two unrelated families of Egyptian descent with hemizygous pathogenic variants in PQBP1. The three patients of the first family displayed the typical features underlying PQBP1 such as the long triangular face, bulbous nose, hypoplastic malar region, and micrognathia, which were subsequently confirmed using targeted sequence analysis that showed a previously reported nonsense mutation c.586C>T p.R196*. Whole exome sequencing identified a novel missense PQBP1 variant c.530G>A:p.R177H in the second family, in which the index patient presented with intellectual disability and dysmorphic facial features reminiscent of Kabuki-like syndrome and his brain magnetic resonance imaging revealed partial agenesis of corpus callosum, mild vermis, and brainstem hypoplasia. These imaging features are distinct from the previously described with a well-known phenotype that is already known for PQBP1. This report expands the phenotypic spectrum of PQBP1-related disorders and is the second reported missense PQBP1 variant. Further, it highlights the possible role of PQBP1 in hindbrain development.

First Korean Case of Renpenning Syndrome with Novel Mutation in PQBP1 Diagnosed by Targeted Exome Sequencing, and Literature Review

Renpenning syndrome is a rare X-linked disorder characterized by mental retardation, leanness, microcephaly, facial dysmorphism, short stature, and small testes. This disease is caused by PQBP1 mutations. Herein, we present a literature review and describe the clinical and molecular findings in a Korean boy with Renpenning syndrome. A 23-month-old boy presented with mental retardation, narrow face, bulbous nose, and cardiac anomaly. Interestingly, targeted exome sequencing identified a novel mutation c.559delT (p.Tyr187llefs*8) in the PQBP1 gene, and he was diagnosed as having Renpenning syndrome. In line with previously reported studies, our case suggests that men with mental retardation, short stature, and microcephaly should include Renpenning syndrome as a differential diagnosis.

Polyglutamine binding protein 1 (PQBP1) inhibits innate immune responses to cytosolic DNA

Recent studies have highlighted the importance of immune sensing of cytosolic DNA of both pathogen and host origin. We aimed to examine the role of DNA sensors interferon-γ-inducible protein 16 (IFI16) and cyclic GMP-AMP synthase (cGAS) in responding to cytosolic DNA. We show IFI16 and cGAS can synergistically induce IFNb transcriptional activity in response to cytoplasmic DNA. We also examined the role of polyglutamine binding protein 1 (PQBP1), a protein predominantly expressed in lymphoid and myeloid cells that has been shown to lead to type I interferon production in response to retroviral infection. We show PQBP1 associates with cGAS and IFI16 in THP-1 cells. Unexpectedly, knockout of PQBP1 in THP-1 cells causes significantly increased type I IFN production in response to transfected cytosolic nucleic acids or DNA damage, unlike what is seen in response to retroviral infection. Overexpression of PQBP1 in HEK293 T cells impairs IFI16/cGAS-induced IFNb transcriptional activity. In human cancer patients, low expression of PQBP1 is correlated with improved survival, the opposite correlation of that seen with cGAS or IFI16 expression. Our findings suggest that PQBP1 inhibits IFI16/cGAS-induced signaling in response to cytosolic DNA, in contrast to the role of this protein in response to retroviral infection.

Phenotype-genotype correlations in 17 new patients with an Xp11.23p11.22 microduplication and review of the literature

Array comparative genomic hybridization (array CGH) has proven its utility in uncovering cryptic rearrangements in patients with X-linked intellectual disability. In 2009, Giorda et al. identified inherited and de novo recurrent Xp11.23p11.22 microduplications in two males and six females from a wide cohort of patients presenting with syndromic intellectual disability. To date, 14 females and 5 males with an overlapping microduplication have been reported in the literature. To further characterize this emerging syndrome, we collected clinical and microarray data from 17 new patients, 10 females, and 7 males. The Xp11.23p11.2 microduplications detected by array CGH ranged in size from 331 Kb to 8.9 Mb. Five patients harbored 4.5 Mb recurrent duplications mediated by non-allelic homologous recombination between segmental duplications and 12 harbored atypical duplications. The chromosomal rearrangement occurred de novo in eight patients and was inherited in six affected males from three families. Patients shared several common major characteristics including moderate to severe intellectual disability, early onset of puberty, language impairment, and age related epileptic syndromes such as West syndrome and focal epilepsy with activation during sleep evolving in some patients to continuous spikes-and-waves during slow sleep. Atypical microduplications allowed us to identify minimal critical regions that might be responsible for specific clinical findings of the syndrome and to suggest possible candidate genes: FTSJ1 and SHROOM4 for intellectual disability along with PQBP1 and SLC35A2 for epilepsy. Xp11.23p11.22 microduplication is a recently-recognized syndrome associated with intellectual disability, epilepsy, and early onset of puberty in females. In this study, we propose several genes that could contribute to the phenotype.

The splicing factor PQBP1 regulates mesodermal and neural development through FGF signaling

Alternative splicing of pre-mRNAs is an important means of regulating developmental processes, yet the molecular mechanisms governing alternative splicing in embryonic contexts are just beginning to emerge. Polyglutamine-binding protein 1 (PQBP1) is an RNA-splicing factor that, when mutated, in humans causes Renpenning syndrome, an X-linked intellectual disability disease characterized by severe cognitive impairment, but also by physical defects that suggest PQBP1 has broader functions in embryonic development. Here, we reveal essential roles for PQBP1 and a binding partner, WBP11, in early development of Xenopus embryos. Both genes are expressed in the nascent mesoderm and neurectoderm, and morpholino knockdown of either causes defects in differentiation and morphogenesis of the mesoderm and neural plate. At the molecular level, knockdown of PQBP1 in Xenopus animal cap explants inhibits target gene induction by FGF but not by BMP, Nodal or Wnt ligands, and knockdown of either PQBP1 or WBP11 in embryos inhibits expression of fgf4 and FGF4-responsive cdx4 genes. Furthermore, PQBP1 knockdown changes the alternative splicing of FGF receptor-2 (FGFR2) transcripts, altering the incorporation of cassette exons that generate receptor variants (FGFR2 IIIb or IIIc) with different ligand specificities. Our findings may inform studies into the mechanisms underlying Renpenning syndrome.