Musashi-2 (MSI2) regulation of DNA damage response in lung cancer

Lung cancer is one of the most common types of cancer worldwide. Non-small cell lung cancer (NSCLC), typically caused by KRAS and TP53 driver mutations, represents the majority of all new lung cancer diagnoses. Overexpression of the RNA-binding protein (RBP) Musashi-2 (MSI2) has been associated with NSCLC progression. To investigate the role of MSI2 in NSCLC development, we compared the tumorigenesis in mice with lung-specific Kras-activating mutation and Trp53 deletion, with and without Msi2 deletion (KPM2 versus KP mice). KPM2 mice showed decreased lung tumorigenesis in comparison with KP mice. In addition, KPM2 lung tumors showed evidence of decreased proliferation, but increased DNA damage, marked by increased levels of phH2AX (S139) and phCHK1 (S345), but decreased total and activated ATM. Using cell lines from KP and KPM2 tumors, and human NSCLC cell lines, we found that MSI2 directly binds ATM mRNA and regulates its translation. MSI2 depletion impaired DNA damage response (DDR) signaling and sensitized human and murine NSCLC cells to treatment with PARP inhibitors in vitro and in vivo. Taken together, we conclude that MSI2 supports NSCLC tumorigenesis, in part, by supporting repair of DNA damage by controlling expression of DDR proteins. These results suggest that targeting MSI2 may be a promising strategy for lung cancers treated with DNA-damaging agents.

The molecular complexity of COL2A1 splicing variants and their significance in phenotype severity

Pathogenic single nucleotide variants (SNVs) found in the COL2A1 gene are associated with a broad range of skeletal dysplasias due to their impact on the structure and function of the Col2a1 protein. However, the molecular mechanisms of some nucleotide variants detected during diagnostic testing remain unclear. The interpretation of missense and splicing variants caused by SNVs poses a significant challenge for clinicians. In this work, we analyzed 22 splicing variants in the COL2A1 gene which have been found in patients with COL2A1-associated skeletal dysplasias. Using a minigene system, we investigated the impact of these SNVs on splicing and gained insights into their molecular mechanisms and genotype-phenotype correlations for each patient. The results of our study are very useful for improving the accuracy of diagnosis and the management of patients with skeletal dysplasias caused by SNVs in the COL2A1 gene.

NSD1 supports cell growth and regulates autophagy in HPV-negative head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. Despite advances in therapeutic management and immunotherapy, the 5-year survival rate for head and neck cancer remains at ~66% of all diagnosed cases. A better definition of drivers of HPV-negative HNSCC that are targetable points of tumor vulnerability could lead to significant clinical advances. NSD1 is a histone methyltransferase that catalyzes histone H3 lysine 36 di-methylation (H3K36me2); mutations inactivating NSD1 have been linked to improved outcomes in HNSCC. In this study, we show that NSD1 induces H3K36me2 levels in HNSCC and that the depletion of NSD1 reduces HNSCC of cell growth in vitro and in vivo. We also find that NSD1 strongly promotes activation of the Akt/mTORC1 signaling pathway. NSD1 depletion in HNSCC induces an autophagic gene program activation, causes accumulation of the p62 and LC3B-II proteins, and decreases the autophagic signaling protein ULK1 at both protein and mRNA levels. Reflecting these signaling defects, the knockdown of NSD1 disrupts autophagic flux in HNSCC cells. Taken together, these data identify positive regulation of Akt/mTORC1 signaling and autophagy as novel NSD1 functions in HNSCC, suggesting that NSD1 may be of value as a therapeutic target in this cancer.

Functional Characterization of Two Novel Intron 4 SERPING1 Gene Splice Site Pathogenic Variants in Families with Hereditary Angioedema

Variants that affect splice sites comprise 14.3% of all pathogenic variants in the SERPING1 gene; more than half of them are located outside the canonical sites. To make a clinical decision concerning patients with such variants, it is essential to know the exact way in which the effect of the variant would be realized. The optimal approach to determine the consequences is considered to be mRNA analysis. In the current study, we present the results of functional analysis of two previously non-described variants in the SERPING1 gene (NM_000062.3) affecting intron 4: c.686-1G>A and c.685+4dup, which were detected in members of two Russian families with autosomal dominant inheritance of angioedema type 1. Analysis of the patients' mRNA (extracted from whole blood) showed that the SERPING1(NM_000062.3):c.685+4dup variant leads to the loss of the donor splice site and the activation of the cryptic site in exon 4: r.710_745del (p.Gly217_Pro228del), while the SERPING1(NM_000062.3):c.686-1G>A variant leads to the skipping of exon 5: r.746_949del (p.Asp229_Ser296del).

Generation of induced pluripotent stem cell line (RCMGi012-A) from fibroblasts of patient with mucopolysaccharidosis type VI

Skin fibroblasts obtained from a 5-year-old girl with genetically proven (two heterozygous mutations in ARSB gene) and clinically manifested mucopolysaccharidosis type VI were successfully transformed into induced pluripotent stem cells by using Sendai virus-based reprogramming vectors including the four Yamanaka factors namely SOX2, OCT3/4, KLF4, and c-MYC. These iPSCs expressed pluripotency markers, had a normal karyotype and the potential to differentiate into three germ layers in spontaneous differentiation assay. The line may be used for cell differentiation and pharmacological investigations, and also may provide a model for development of a personalized treatment including drug screening and genome editing.

NSD1 supports cell growth and regulates autophagy in HPV-negative head and neck squamous cell carcinoma

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. Despite advances in therapeutic management and immunotherapy, the five-year survival rate for head and neck cancer remains at ~66% of all diagnosed cases. A better definition of drivers of HPV-negative HNSCC that are targetable points of tumor vulnerability could lead to significant clinical advances. NSD1 is a histone methyltransferase which catalyzes histone H3 lysine 36 di-methylation (H3K36me2); mutations inactivating NSD1 have been linked to improved outcomes in HNSCC. In this study, we show that NSD1 induces H3K36me2 levels in HNSCC, and that the depletion of NSD1 reduces HNSCC of cell growth in vitro and in vivo. We also find that NSD1 strongly promotes activation of the Akt/mTORC1 signaling pathway. NSD1 depletion in HNSCC induces an autophagic gene program activation, causes accumulation of the p62 and LC3B-II proteins, and decreases the autophagic signaling protein ULK1 at both protein and mRNA levels. Reflecting these signaling defects, knockdown of NSD1 disrupts autophagic flux in HNSCC cells. Taken together, these data identify positive regulation of Akt/mTORC1 signaling and autophagy as novel NSD1 functions in HNSCC, suggesting that NSD1 may be of value as a therapeutic target in this cancer.

Functional investigation of SCN1A deep-intronic variants activating poison exons inclusion

Dravet syndrome is a devastating epileptic syndrome characterized by intractable epilepsy with an early age of onset, regression of developmental milestones, ataxia, and motor deficits. Loss-of-function pathogenic variants in the SCN1A gene are found in the majority of patients with Dravet syndrome; however, a significant number of patients remain undiagnosed even after comprehensive genetic testing. Previously, it was shown that intronic elements in the SCN1A gene called poison exons can incorporate into SCN1A mRNA, leading to haploinsufficiency and potentially causing Dravet syndrome. Here, we developed a splicing reporter assay for all described poison exons of the SCN1A gene and validated it using previously reported and artificially introduced variants. Overall, we tested 18 deep-intronic single nucleotide variants and one complex allele in the SCN1A gene. Our approach is capable of evaluating the effect of both variants affecting cis-regulatory sequences and splice-site variants, with the potential to functionally annotate every possible variant within these elements. Moreover, using antisense-modified uridine-rich U7 small nuclear RNAs, we were able to block poison exon incorporation in mutant constructs, an approach that could be used as a promising therapeutic intervention in Dravet syndrome patients with deep-intronic variants.

Musashi-2 (MSI2) regulation of DNA damage response in lung cancer

Lung cancer is one of the most common types of cancers worldwide. Non-small cell lung cancer (NSCLC), typically caused by KRAS and TP53 driver mutations, represents the majority of all new lung cancer diagnoses. Overexpression of the RNA-binding protein (RBP) Musashi-2 (MSI2) has been associated with NSCLC progression. To investigate the role of MSI2 in NSCLC development, we compared the tumorigenesis in mice with lung-specific Kras -activating mutation and Trp53 deletion, with and without Msi2 deletion (KP versus KPM2 mice). KPM2 mice showed decreased lung tumorigenesis in comparison with KP mice what supports published data. In addition, using cell lines from KP and KPM2 tumors, and human NSCLC cell lines, we found that MSI2 directly binds ATM/Atm mRNA and regulates its translation. MSI2 depletion impaired DNA damage response (DDR) signaling and sensitized human and murine NSCLC cells to treatment with PARP inhibitors in vitro and in vivo . Taken together, we conclude that MSI2 supports lung tumorigenesis, in part, by direct positive regulation of ATM protein expression and DDR. This adds the knowledge of MSI2 function in lung cancer development. Targeting MSI2 may be a promising strategy to treat lung cancer.

Significance

This study shows the novel role of Musashi-2 as regulator of ATM expression and DDR in lung cancer.

Regulation of VEGFR2 and AKT Signaling by Musashi-2 in Lung Cancer

Lung cancer is the most frequently diagnosed cancer type and the leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) represents most of the diagnoses of lung cancer. Vascular endothelial growth factor receptor-2 (VEGFR2) is a member of the VEGF family of receptor tyrosine kinase proteins, which are expressed on both endothelial and tumor cells, are one of the key proteins contributing to cancer development, and are involved in drug resistance. We previously showed that Musashi-2 (MSI2) RNA-binding protein is associated with NSCLC progression by regulating several signaling pathways relevant to NSCLC. In this study, we performed Reverse Protein Phase Array (RPPA) analysis of murine lung cancer, which suggests that VEGFR2 protein is strongly positively regulated by MSI2. Next, we validated VEGFR2 protein regulation by MSI2 in several human lung adenocarcinoma cell line models. Additionally, we found that MSI2 affected AKT signaling via negative PTEN mRNA translation regulation. In silico prediction analysis suggested that both VEGFR2 and PTEN mRNAs have predicted binding sites for MSI2. We next performed RNA immunoprecipitation coupled with quantitative PCR, which confirmed that MSI2 directly binds to VEGFR2 and PTEN mRNAs, suggesting a direct regulation mechanism. Finally, MSI2 expression positively correlated with VEGFR2 and VEGF-A protein levels in human lung adenocarcinoma samples. We conclude that the MSI2/VEGFR2 axis contributes to lung adenocarcinoma progression and is worth further investigations and therapeutic targeting.

Regulation of VEGFR2 and AKT signaling by Musashi-2 in lung cancer

Lung cancer is the most frequently diagnosed cancer type and the leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) represents most of the lung cancer. Vascular endothelial growth factor receptor-2 (VEGFR2) is a member of the VEGF family of receptor tyrosine kinase proteins, expressed on both endothelial and tumor cells which is one of the key proteins contributing to cancer development and involved in drug resistance. We previously showed that Musashi-2 (MSI2) RNA-binding protein is associated with NSCLC progression by regulating several signaling pathways relevant to NSCLC. In this study, we performed Reverse Protein Phase Array (RPPA) analysis of murine lung cancer which nominated VEGFR2 protein as strongly positively regulated by MSI2. Next, we validated VEGFR2 protein regulation by MSI2 in several human NSCLC cell line models. Additionally, we found that MSI2 affected AKT signaling via negative PTEN mRNA translation regulation. In silico prediction analysis suggested that both VEGFR2 and PTEN mRNAs have predicted binding sites for MSI2. We next performed RNA immunoprecipitation coupled with quantitative PCR which confirmed that MSI2 directly binds to VEGFR2 and PTEN mRNAs, suggesting direct regulation mechanism. Finally, MSI2 expression positively correlated with VEGFR2 and VEGF-A protein levels in human NSCLC samples. We conclude that MSI2/VEGFR2 axis contributes to NSCLC progression and is worth further investigations and therapeutic targeting.

Rationally designed inhibitors of the Musashi protein-RNA interaction by hotspot mimicry

RNA-binding proteins (RBPs) are key post-transcriptional regulators of gene expression, and thus underlie many important biological processes. Here, we developed a strategy that entails extracting a "hotspot pharmacophore" from the structure of a protein-RNA complex, to create a template for designing small-molecule inhibitors and for exploring the selectivity of the resulting inhibitors. We demonstrate this approach by designing inhibitors of Musashi proteins MSI1 and MSI2, key regulators of mRNA stability and translation that are upregulated in many cancers. We report this novel series of MSI1/MSI2 inhibitors is specific and active in biochemical, biophysical, and cellular assays. This study extends the paradigm of "hotspots" from protein-protein complexes to protein-RNA complexes, supports the "druggability" of RNA-binding protein surfaces, and represents one of the first rationally-designed inhibitors of non-enzymatic RNA-binding proteins. Owing to its simplicity and generality, we anticipate that this approach may also be used to develop inhibitors of many other RNA-binding proteins; we also consider the prospects of identifying potential off-target interactions by searching for other RBPs that recognize their cognate RNAs using similar interaction geometries. Beyond inhibitors, we also expect that compounds designed using this approach can serve as warheads for new PROTACs that selectively degrade RNA-binding proteins.

Rationally designed inhibitors of the Musashi protein-RNA interaction by hotspot mimicry

RNA-binding proteins (RBPs) are key post-transcriptional regulators of gene expression, and thus underlie many important biological processes. Here, we developed a strategy that entails extracting a "hotspot pharmacophore" from the structure of a protein-RNA complex, to create a template for designing small-molecule inhibitors and for exploring the selectivity of the resulting inhibitors. We demonstrate this approach by designing inhibitors of Musashi proteins MSI1 and MSI2, key regulators of mRNA stability and translation that are upregulated in many cancers. We report this novel series of MSI1/MSI2 inhibitors is specific and active in biochemical, biophysical, and cellular assays. This study extends the paradigm of "hotspots" from protein-protein complexes to protein-RNA complexes, supports the "druggability" of RNA-binding protein surfaces, and represents one of the first rationally-designed inhibitors of non-enzymatic RNA-binding proteins. Owing to its simplicity and generality, we anticipate that this approach may also be used to develop inhibitors of many other RNA-binding proteins; we also consider the prospects of identifying potential off-target interactions by searching for other RBPs that recognize their cognate RNAs using similar interaction geometries. Beyond inhibitors, we also expect that compounds designed using this approach can serve as warheads for new PROTACs that selectively degrade RNA-binding proteins.

Expanding the genetic spectrum of the pyruvate carboxylase deficiency with novel missense, deep intronic and structural variants

Introduction

Pathogenic variants in the pyruvate carboxylase (PC) gene cause a wide spectrum of recessive phenotypes, ranging from the early-onset fatal encephalopathy to the adult-onset benign form.

Results

Patient 1 is a 6 y.o. boy with ataxia, hypoglycemia and episodes of lactic acidosis. WGS revealed the novel heterozygous missense variant c.1372A > G (p.Asn458Asp) in the PC gene. Additional analysis revealed discordant reads mapped to chromosomes 11 and 1, so a reciprocal translocation disrupted the PC gene was suspected. The translocation was validated via FISH-analysis and Sanger sequencing of its boundaries.

Patient 2 is a 13 y.o. girl with psychomotor delay, episodes of lactic acidosis and ketonuria. WES revealed the novel homozygous intronic variant c.1983-116C > T. The PC's mRNA analysis demonstrated the exonization of several intron 16 sequences and some residual amount of WT mRNA isoform.

Two other patients had more severe course of the disease. Their genotype represents missense variants in compound heterozygous and homozygous state (c.1876C > T (p.Arg626Trp), c.2606G > C (p.Gly869Ala), c.2435C > A (p.Ala812Asp).

Conclusion

In patients with metabolic crises, lactic acidosis and hypoglycemia analysis of PC gene is recommended. WGS with deep bioinformatic analysis should be taken into consideration when none or the only one pathogenic variant in the PC gene is found.

•

In patients with metabolic crises with lactic acidosis and hypoglycemia WGS with deep bioinformatic analysis should be taken when none or the only one heterozygous pathogenic variant in the PC gene is found.

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PC gene may have more deep intronic pathogenic variants than included in known mutation databases.

Abstract 874: MSI2 regulates VEGFR2 signaling and tumor progression in NSCLC

Lung cancer holds second place in incidence and first place in mortality among all cancers, both in men and women, with metastasis contributing to the vast majority of deaths. Recently, expression of vascular endothelial growth factor receptor-2 (VEGFR2) on both endothelial and tumor cells was demonstrated as one of the key mechanisms contributing to growth of non-small cell lung cancer (NSCLC), the most common subtype of lung cancer. VEGFR2 dependent signaling is critical both for tumor autocrine functions related to NSCLC migration, and in paracrine control of tumor angiogenesis through action on tumor-proximal endothelial cells, suggesting a potential mechanism for growth control. Several drugs targeting VEGFR2 signaling pathway demonstrated their clinical efficacy in NSCLC setting, including VEGFR2 and VEGF-A inhibitors, VEGF-A/PIGF trap. Recently our group demonstrated that RNA-binding protein Musashi-2 (MSI2) is driving progression and metastasis of NSCLC. MSI2 regulates mRNA translation of multiple targets, its expression is upregulated in the metastasis-competent murine and human lung cancer cell lines and is progressively elevated in lung cancer samples. The goal of this study is to define the role of MSI2 in sustaining VEGFR2 signaling during NSCLC progression. Using reverse RNA immunoprecipitation (RIP) qPCR analysis, we demonstrate that MSI2 directly binds VEGFR2 mRNA. Reverse protein phase array (RPPA) of several NSCLC cell line models with expression or knockdown of MSI2 and subsequent direct validation showed that MSI2 strongly and positively regulates expression of VEGFR2. Subsequent mechanistical analysis revealed that MSI2 knockdown leads to decreased VEGFR2 protein and mRNA levels expression in several NSCLC cell lines in vitro, resulting in increased apoptosis via inhibition of VEGFR2 signaling pathway. To better characterize MSI2 biology, we’ve crossed the B6/129S4-Msi2tm1.1Cjl/J (M2) mice with B6/129S/Sv-Krastm3Tyj/J;Trp53tm1Brn/J (KP) mice and generated novel B6/129S/Sv-KP;Msi2-/- (KPM2) mouse model. Induction of tumorigenesis in KP mice using Cre adenovirus leads to development of lung adenocarcinoma. Induction of lung-specific Cre resulted in tumorigenesis in both KP and KPM2 mice. Interestingly, we observed significant decrease in both total lung tumor number and total lung tumor burden in KPM2 compared to KP mice. Next, we established three novel KP and KPM2 derived cell lines from mouse lung tumors and found that KPM2 cell lines demonstrate reduced proliferation capacity and VEGFR2 mRNA level relative to KP cell lines. Additional studies to understand an impact of MSI2 deletion in KP cell lines are ongoing. Taken together, MSI2 is a promising target for NSCLC treatment, as this protein regulates VEGFR2 signaling and apoptosis in cell models and contributes to KP tumorigenesis in vivo.

Citation Format: Igor Bychkov, Alexander Deneka, Iuliia Topchu, Petr Makhov, Alexander Kudinov, Anna Nikonova, John Karanicolas, Erica Golemis, Christopher Lengner, Hossein Borghaei, Jyoti Patel, Yanis Boumber. MSI2 regulates VEGFR2 signaling and tumor progression in NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 874.

Abstract 3718: NSD histone methyltransferases drive cell proliferation in HPV-negative head and neck squamous cell carcinoma (HNSCC)

Histone modifications play important role in regulating the function and structure of chromatin. Abnormal histone methylation is often detected during tumor development and progression. NSD1, NSD2, and NSD3 are key histone methyltransferases (HMTs) that catalyze lysine 36 dimethylation (K36me2) at histone H3. Inactivating NSD1 mutations are frequent in head neck squamous cell carcinoma (HNSCC) commonly occur in HPV-negative oropharyngeal (OP) carcinoma and laryngeal carcinomas (LC), and define a novel prognostic subtype in LC, where they associate with dramatically improved overall and progression-free survival. Here, we explored the biological impact of the loss of function of NSD1 in head neck squamous carcinoma (HNSCC). First, we discovered that HNSCC cells with a damaging mutation in NSD1 have reduced K36me2 methylation levels relative to NSD1 wild-type HNSCC cells. Second, we also found slower cell proliferation in NSD1 mutant cell line (SCC4) in comparison with other NSD1 WT cell lines. To further investigate the biologic impact of NSDs, we knocked down NSD1 and NSD2 with shRNA in different histologic subtypes of HNSCC cell lines (JHU011, JHU022, Cal27, and FaDu cell lines). We discovered that depletion of NSD1 and NSD2 results in a reduction of K36me2 and a significant decrease in cell proliferation and clonogenic formation in HNSCC, but not in lung cancer cells. Next, we performed a flow cytometry-based assay and found that NSD1/NSD2 depletion in HNSCC cells causes a significant increase in apoptosis level. We also probed for gene expression and signaling in HNSCC cells following NSD1 depletion using RNA sequencing and reverse protein phase array (RPPA) approaches. From a list of RPPA candidate targets of NSD1, we confirmed the decrease in the protein and mRNA level of Phosphatidylinositol-5-Phosphate 4-Kinase Type 2 Beta (PIP4K2B), but not other members of this family (PIP4K2A and PIP4K2C). PIP4K2B may regulate the ratio of lipid messengers PI5P and PI(4,5)P2 (substrate and reaction product, respectively). The level of phosphorylation of mitogen-activated kinase p70S6 was also decreased under NSD1 knockdown. PIP4K2B siRNA depletion has also led to a significant decrease in HNSCC proliferation. Taken together, this data supports the idea that NSD1 is required for HNSCC cell proliferation via PIP4K2B. Downstream signaling, gene expression effects, and possible cell cycle regulation by NSD enzymes remain to be investigated in more detail. Further, NSDs might be attractive targets for drug development, and targeting NSD1/NSD2 enzymes may be a new strategy for improving outcomes in HNSCC patients.

Citation Format: Iuliia Topchu, Rajendra Pangeni, Igor Bychkov, Petr Makhov, John Karanicolas, Jindan Yu, Erica Golemis, Jochen Lorch, Yanis Boumber. NSD histone methyltransferases drive cell proliferation in HPV-negative head and neck squamous cell carcinoma (HNSCC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3718.

WITHDRAWN: A novel deployment strategy of monitors for vehicle emission remote sensing system

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Complex Transposon Insertion as a Novel Cause of Pompe Disease

Pompe disease (OMIM#232300) is an autosomal recessive lysosomal storage disorder caused by mutations in the GAA gene. According to public mutation databases, more than 679 pathogenic variants have been described in GAA, none of which are associated with mobile genetic elements. In this article, we report a novel molecular genetic cause of Pompe disease, which could be hardly detected using routine molecular genetic analysis. Whole genome sequencing followed by comprehensive functional analysis allowed us to discover and characterize a complex mobile genetic element insertion deep in the intron 15 of the GAA gene in a patient with infantile onset Pompe disease.

Impaired complex I repair causes recessive Leber's hereditary optic neuropathy

Leber’s hereditary optic neuropathy (LHON) is the most frequent mitochondrial disease and was the first to be genetically defined by a point mutation in mitochondrial DNA (mtDNA). A molecular diagnosis is achieved in up to 95% of cases, the vast majority of which are accounted for by 3 mutations within mitochondrial complex I subunit–encoding genes in the mtDNA (mtLHON). Here, we resolve the enigma of LHON in the absence of pathogenic mtDNA mutations. We describe biallelic mutations in a nuclear encoded gene, DNAJC30, in 33 unsolved patients from 29 families and establish an autosomal recessive mode of inheritance for LHON (arLHON), which to date has been a prime example of a maternally inherited disorder. Remarkably, all hallmarks of mtLHON were recapitulated, including incomplete penetrance, male predominance, and significant idebenone responsivity. Moreover, by tracking protein turnover in patient-derived cell lines and a DNAJC30-knockout cellular model, we measured reduced turnover of specific complex I N-module subunits and a resultant impairment of complex I function. These results demonstrate that DNAJC30 is a chaperone protein needed for the efficient exchange of complex I subunits exposed to reactive oxygen species and integral to a mitochondrial complex I repair mechanism, thereby providing the first example to our knowledge of a disease resulting from impaired exchange of assembled respiratory chain subunits.

A Family Case of Congenital Myasthenic Syndrome-22 Induced by Different Combinations of Molecular Causes in Siblings

Congenital myasthenic syndrome-22 (CMS22, OMIM 616224) is a very rare recessive hereditary disorder. At the moment, ten CMS22 patients are described, with the disorder caused by nine different Loss-of-Function mutations and 14 gross deletions in the PREPL gene. The materials for our study were DNA samples of five family members: two patients with myasthenia, their healthy sibling and parents. Clinical exome analysis was carried out for one patient, then the whole family was checked for target variants with Sanger sequencing, quantitative multiplex ligation-dependent probe amplification, and chromosome 2 microsatellite markers study. To determine the functional significance of the splicing variant, we applied the minigene assay. The cause of the proband's disorder is a compound heterozygous state of two previously non-described pathogenic PREPL variants: a c.1528C>T (p.(Arg510Ter)) nonsense mutation and a c.2094G>T pseudo-missense variant, which, simultaneously with a p.(Lys698Asn) amino acid substitution, affects splicing, leading to exon 14 skipping in mRNA. The second patient's disorder was caused by a homozygous nonsense c.1528C>T (p.(Arg510Ter)) mutation due to maternal uniparental disomy (UPD) of chromosome 2. In this study, we describe a unique case, in which two siblings with a rare disorder have different pathologic genotypes.

Prognostic significance of Musashi 2 (MSI2) RNA-binding protein expression in precancerous polyps and during colorectal cancer (CRC) progression

e16009

Background: The RNA-binding protein Musashi-2 (MSI2) controls the translation of proteins that support stem cell identity and lineage determination. Elevated expression of MSI2 plays an important role during progression, dissemination, and drug resistance in numerous solid and hematological malignancies. This study assessed MSI2 as potential clinical biomarker in colorectal cancer (CRC) and pre-malignant disorders of colon mucosa. Methods: This study included 125 patients, of whom 20 had tubulovillous adenomas (TAs) of the colon, and 105 had verified colorectal cancer. Of the 105 patients with CRC, 45 had locoregional invasion (stages I-III). The remaining 60 patients had liver metastases (mCRC), with 31 patients diagnosed with synchronous and 29 with metachronous metastases. We used immunohistochemical (IHC) approach to measure MSI2 expression in matching specimens of normal versus TA tissues, normal versus primary CRC tumor, and normal versus metastatic CRC, followed by correlative analysis in relation to clinical outcomes. In parallel, the biological effects of overexpressing or depleting MSI2 expression in human CRC cells were analyzed in vitro using qRT-PCR, western blot, proliferation and clonogenic assays. Results: MSI2 expression in patient samples was significantly elevated in TAs versus primary tissue (p < 0.002), and was further elevated in primary tumor, and in metastatic sites (p < 0.0001 versus normal tissue, p < 0.003 versus TAs). MSI2 expression positively correlated with decreased progression free survival (PFS) and overall survival (OS), lower tumor grade, and right-side localization (p = 0.004) of tumors. In vitro knockdown of MSI2 in CRC cells suppressed of proliferation, survival and clonogenic capacities of the cells. Conclusions: Elevated expression of MSI2 is associated with pre-cancerous polyps (TAs) in the colonic mucosa, indicating it is an early event in transformation. MSI2 is further elevated during, CRC progression, and associated with poor prognosis, and loss of MSI2 reduces multiple growth properties of CRC cell models. These data imply a causative role of MSI2 overexpression at multiple stages of CRC formation and progression.

Mitochondrial DNA Variation of Leber's Hereditary Optic Neuropathy in Western Siberia

Our data first represent the variety of Leber's hereditary optic neuropathy (LHON) mutations in Western Siberia. LHON is a disorder caused by pathogenic mutations in mitochondrial DNA (mtDNA), inherited maternally and presents mainly in young adults, predominantly males. Clinically, LHON manifests itself as painless central vision loss, resulting in early onset of disability. The epidemiology of LHON has not been fully investigated yet. In this study, we report 44 genetically unrelated families with LHON manifestation. We performed whole mtDNA genome sequencing and provided genealogical and molecular genetic data on mutations and haplogroup background of LHON patients. Known "primary" pathogenic mtDNA mutations (MITOMAP) were found in 32 families: m.11778G>A represents 53.10% (17/32), m.3460G>A-21.90% (7/32), m.14484T>C-18.75% (6/32), and rare m.10663T>C and m.3635G>A represent 6.25% (2/32). We describe potentially pathogenic m.4659G>A in one subject without known pathogenic mutations, and potentially pathogenic m.6261G>A, m.8412T>C, m.8551T>C, m.9444C>T, m.9921G>A, and m.15077G>A in families with known pathogenic mutations confirmed. We suppose these mutations could contribute to the pathogenesis of optic neuropathy development. Our results indicate that haplogroup affiliation and mutational spectrum of the Western Siberian LHON cohort substantially deviate from those of European populations.

Abstract 955: Musashi-2 regulates EGFR expression in NSCLC, cell proliferation and survival, response to EGFR inhibitors in EGFR-mutant NSCLC

Musashi-2 (MSI2) is an RNA-binding protein that regulates mRNA translation. We recently established that MSI2 is elevated in a subset of non-small cell lung cancer (NSCLC) tumors upon progression and drives NSCLC metastasis, in part based on activity supporting a TGF-beta/SMAD3/claudin signaling cascade. Here, reverse phase protein array (RPPA) analysis of MSI2-depleted versus control KrasLA1/+;P53R172HΔG/+ murine NSCLC cell lines identified a significant upregulation of HER3 (ERBB3) upon MSI2 depletion. Negative MSI2-dependent regulation of ERBB3 protein was confirmed in multiple murine and human NSCLC models, based on analysis of MSI2 depletion or overexpression. Further, MSI2 positively regulated expression of the epidermal growth factor receptor (EGFR) protein in the same models. Comparing EGFR and KRAS driven models, we found that MSI2 depletion significantly impairs cell proliferation and clonogenicity only in EGFR-mutant NSCLC cell lines. Using RNA immunoprecipitation analysis coupled with qPCR, we show that MSI2 directly binds to EGFR and, to a lesser extent, to HER3 mRNA. MSI2 mRNA binding was correlating with the presence of predicted MSI2 binding sites in corresponding mRNAs. Taken together, this data suggest direct regulation of EGFR protein expression by MSI2 at post transcriptional level. NSCLC lung tissue microarray immunohistochemistry analysis revealed that MSI2 total positivity by H-score, 2+/3+ and 3+ positivity correlated with EGFR 3+ staining. Finally, EGFR inhibitors erlotinib and afatinib synergized with MSI2 depletion in EGFR mutant models, suggesting that therapeutic targeting of MSI2 could be of clinical value, especially in EGFR-mutant lung cancer. In vivo experiments of erlotinib treatments of wild type or MSI2 depleted tumors are ongoing and these results will be presented.

Citation Format: Alexander Kudinov, Petr Makhov, Bulat Faezov, Igor Bychkov, Alexander Deneka, Emmanuelle Nicolas, Kathy Q Q. Caid, Rohan Brebione, Eleanor Avrilf, Anna S. Nikonova, Ilya G. Serebriiskii, Hossein Borghaei, Erica A. Golemis, Yanis Boumber. Musashi-2 regulates EGFR expression in NSCLC, cell proliferation and survival, response to EGFR inhibitors in EGFR-mutant NSCLC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 955.