Lihasdystrofiaproteiini myotiliinin molekulaariset sidokset ja hajoamiseen liittyvät mekanismit

The striated muscle sarcomere is a force generating and transducing unit as well as an important sensor of extracellular cues and a coordinator of cellular signals. The borders of individual sarcomeres are formed by the Z-disks. The Z-disk component myotilin interacts with Z-disk core structural proteins and with regulators of signaling cascades. Missense mutations in the gene encoding myotilin cause dominantly inherited muscle disorders, myotilinopathies, by an unknown mechanism. In this thesis the functions of myotilin were further characterized to clarify the molecular biological basis and the pathogenetic mechanisms of inherited muscle disorders, mainly caused by mutated myotilin. Myotilin has an important function in the assembly and maintenance of the Z-disks probably through its actin-organizing properties. Our results show that the Ig-domains of myotilin are needed for both binding and bundling actin and define the Ig domains as actin-binding modules. The disease-causing mutations appear not to change the interplay between actin and myotilin. Interactions between Z-disk proteins regulate muscle functions and disruption of these interactions results in muscle disorders. Mutations in Z-disk components myotilin, ZASP/Cypher and FATZ-2 (calsarcin-1/myozenin-2) are associated with myopathies. We showed that proteins from the myotilin and FATZ families interact via a novel and unique type of class III PDZ binding motif with the PDZ domains of ZASP and other Enigma family members and that the interactions can be modulated by phosphorylation. The morphological findings typical of myotilinopathies include Z-disk alterations and aggregation of dense filamentous material. The causes and mechanisms of protein aggregation in myotilinopathy patients are unknown, but impaired degradation might explain in part the abnormal protein accumulation. We showed that myotilin is degraded by the calcium-dependent, non-lysosomal cysteine protease calpain and by the proteasome pathway, and that wild type and mutant myotilin differ in their sensitivity to degradation. These studies identify the first functional difference between mutated and wild type myotilin. Furthermore, if degradation of myotilin is disturbed, it accumulates in cells in a manner resembling that seen in myotilinopathy patients. Based on the results, we propose a model where mutant myotilin escapes proteolytic breakdown and forms protein aggregates, leading to disruption of myofibrils and muscular dystrophy. In conclusion, the main results of this study demonstrate that myotilin is a Z-disk structural protein interacting with several Z-disk components. The turnover of myotilin is regulated by calpain and the ubiquitin proteasome system and mutations in myotilin seem to affect the degradation of myotilin, leading to protein accumulations in cells. These findings are important for understanding myotilin-linked muscle diseases and designing treatments for these disorders.Lihaksen rakennetta ja toimintaa säätelevät useat valkuaisaineet, joiden avulla aktiini- ja myosiinisäikeiden tuottama supistusvoima synkronoidaan ja siirretään tukikudoksiin. Myotiliini on lihaksen rakenneproteiini ja osa lihaksen supistusyksikköä, sarkomeeriä. Myotiliinin perityt pistemutaatiot aikaansaavat luuranko- ja sydänlihaksen häiriöitä, eli myotilinopatioita. Vaikka myotilinopatian perinnöllinen tausta tunnetaan, on vielä selvittämättä, kuinka myotiliinin muutokset johtavat lihasten surkastumiseen. Solutasolla tiedämme, että myotilinopatiapotilailla on vakavia sarkomeerin rakennehäiriöitä, ja että viallisen myotiliinin ilmentäminen lihassoluissa johtaa sarkomeerirakenteen hajoamiseen. Tässä tutkimuksessa selvitettiin myotiliinin toimintamekanismeja. Myotiliinin päätehtävänä lienee aktiinisäikeiden yhteenliittäminen sarkomeerin Z-levyssä. Osoitimme, että myotiliinin immunoglobuliinin (Ig) kaltaisia rakenneyksiköitä eli domeeneja tarvitaan aktiinin säätelyyn. Nämä Ig domeenit ovat yhtenäisiä rakenneosia muiden myotiliiniperheen jäsenten kanssa. Tauteja aiheuttavat geenivirheet eivät kuitenkaan vaikuttane myotiliinin ja aktiinin väliseen vuorovaikutukseen. Lihasmassaa säädellään tarpeen mukaan ja esimerkiksi fyysinen harjoittelu kasvattaa lihaksia. Rasitusvastetta ja siihen liittyvää geenien luentaa säätelevät Z-levyn rakenneproteiinit. Häiriö proteiinien, kuten myotiliinin, vuorovaikutuksissa voi johtaa lihastauteihin. Selvitimme sydän- ja lihastaudeissa mutatoituneiden myotiliinin- ja FATZ-perheen proteiinien vuorovaikutusta Z-levyssä sijaitsevien Enigma proteiiniperheen jäsenten kanssa. Osoitimme, että myotiliini- ja FATZ-perheiden jäsenet sitovat Enigma proteiinien PDZ-domeenia uuden ja ainutlaatuisen luokka III:n PDZ:tä sitovan motiivin avulla. Näitä proteiinien vuorovaikutuksia voidaan säädellä fosforylaation avulla. Vuorovaikutukset ovat osa mekanismia, jolla lihassolun sisäinen viestintä tapahtuu. Myotilinopatioille tyypillisiä lihaksen rakennevirheitä ovat Z-levyn muutokset ja tiheän säiemäisen materiaalin keräytyminen. Kertymien syytä ja mekanismia ei tunneta, mutta yksi syy tähän voisi olla proteiinien puutteellinen hajoaminen. Osoitimme, että kalpaiini-proteaasi pilkkoo myotiliinin lihassoluissa ja että myotiliini hajoaa pienempiin rakenneosiin proteasomireitin välityksellä. Määritimme myös ensimmäisen toiminnallisen eron normaalin ja mutatoituneen myotiliinin välillä, sillä myotilinopatioissa mutatoitunut myotiliini hajoaa huomattavasti normaalia hitaammin. Lisäksi näytimme, että mikäli myotiliinin hajoamista estetään kemikaaleilla, seurauksena on proteiinikertymiä, jotka muistuttavat potilasnäytteissä nähtäviä muutoksia. Näiden tulosten perusteella ehdotamme taudin syntymekanismiksi mallia, jossa mutatoitunut myotiliini ei hajoa normaalisti vaan muodostaa kertymiä, jotka johtavat lihaksen rakenneosien hajoamiseen ja lihastautiin. Tulokset edesauttavat myotiliiniin liittyvien lihassairauksien ymmärtämistä ja lihassairauksien hoitoon tarkoitettujen lääkkeiden kehittämistä

Liprin-alpha 1 modulates cancer cell signaling by transmembrane protein CD82 in adhesive membrane domains linked to cytoskeleton

Background: PPFIA1 is located at the 11q13 region commonly amplified in cancer. The protein liprin-alpha 1 encoded by PPFIA1 contributes to the adhesive and invasive structures of cytoskeletal elements and is located at the invadosomes in cancer cells. However, the precise mechanism of liprin-alpha 1 function in cancer progression has remained elusive. Methods: Invasion regulating activity of liprin-alpha 1 was examined by analyzing the functions of squamous cell carcinoma of head and neck (HNSCC) cell lines in three-dimensional collagen I after RNAi mediated gene knockdown. Transcriptome profiling and Gene Set Enrichment Analysis from HNSCC and breast cancer cells were used to identify expression changes relevant to specific cellular localizations, biological processes and signaling pathways after PPFIA1 knockdown. The significance of the results was assessed by relevant statistical methods (Wald and Benjamini-Hochberg). Localization of proteins associated to liprin-alpha 1 was studied by immunofluorescence in 2D and 3D conditions. The association of PPFIA1 amplification to HNSCC patient survival was explored using The Cancer Genome Atlas data. Results: In this study, we show that liprin-alpha 1 regulates biological processes related to membrane microdomains in breast carcinoma, as well as protein trafficking, cell-cell and cell-substrate contacts in HNSCC cell lines cultured in three-dimensional matrix. Importantly, we show that in all these cancer cells liprin-alpha 1 knockdown leads to the upregulation of transmembrane protein CD82, which is a suppressor of metastasis in several solid tumors. Conclusions: Our results provide novel information regarding the function of liprin-alpha 1 in biological processes essential in cancer progression. The results reveal liprin-alpha 1 as a novel regulator of CD82, linking liprin-alpha 1 to the cancer cell invasion and metastasis pathways.Peer reviewe

Liprin-α1 modulates cancer cell signaling by transmembrane protein CD82 in adhesive membrane domains linked to cytoskeleton

Abstract Background PPFIA1 is located at the 11q13 region commonly amplified in cancer. The protein liprin-α1 encoded by PPF1A1 contributes to the adhesive and invasive structures of cytoskeletal elements and is located at the invadosomes in cancer cells. However, the precise mechanism of liprin-α1 function in cancer progression has remained elusive. Methods Invasion regulating activity of liprin-α1 was examined by analyzing the functions of squamous cell carcinoma of head and neck (HNSCC) cell lines in three-dimensional collagen I after RNAi mediated gene knockdown. Transcriptome profiling and Gene Set Enrichment Analysis from HNSCC and breast cancer cells were used to identify expression changes relevant to specific cellular localizations, biological processes and signaling pathways after PPFIA1 knockdown. The significance of the results was assessed by relevant statistical methods (Wald and Benjamini-Hochberg). Localization of proteins associated to liprin-α1 was studied by immunofluorescence in 2D and 3D conditions. The association of PPFIA1 amplification to HNSCC patient survival was explored using The Cancer Genome Atlas data. Results In this study, we show that liprin-α1 regulates biological processes related to membrane microdomains in breast carcinoma, as well as protein trafficking, cell-cell and cell-substrate contacts in HNSCC cell lines cultured in three-dimensional matrix. Importantly, we show that in all these cancer cells liprin-α1 knockdown leads to the upregulation of transmembrane protein CD82, which is a suppressor of metastasis in several solid tumors. Conclusions Our results provide novel information regarding the function of liprin-α1 in biological processes essential in cancer progression. The results reveal liprin-α1 as a novel regulator of CD82, linking liprin-α1 to the cancer cell invasion and metastasis pathways

Gremlin-1 is a key regulator of the invasive cell phenotype in mesothelioma

Peer reviewe

Liprin-alpha 1 is a regulator of vimentin intermediate filament network in the cancer cell adhesion machinery

PPFIA1 is located at the 11q13 region, which is one of the most commonly amplified regions in several epithelial cancers including head and neck squamous cell carcinoma and breast carcinoma. Considering the location of PPFIA1 in this amplicon, we examined whether protein encoded by PPFIA1, liprin-alpha 1, possesses oncogenic properties in relevant carcinoma cell lines. Our results indicate that liprin-alpha 1 localizes to different adhesion and cytoskeletal structures to regulate vimentin intermediate filament network, thereby altering the invasion and growth properties of the cancer cells. In non-invasive cells liprin-alpha 1 promotes expansive growth behavior with limited invasive capacity, whereas in invasive cells liprin-alpha 1 has significant impact on mesenchymal cancer cell invasion in three-dimensional collagen. Current results identify liprin-a1 as a novel regulator of the tumor cell intermediate filaments with differential oncogenic properties in actively proliferating or motile cells.Peer reviewe

Loss of ATRX/DAXX expression and alternative lengthening of telomeres in uterine leiomyomas

Background Uterine leiomyomas (ULs) are the most common gynecologic tumors and affect 3 of every 4 women by the age of 50 years. The majority of ULs are classified as conventional tumors, whereas 10% represent various histopathological subtypes with features that mimic malignancy. These subtypes include cellular and mitotically active ULs and ULs with bizarre nuclei. Uterine leiomyosarcoma (ULMS), the malignant counterpart of UL, is an aggressive cancer with poor overall survival. The early diagnosis and preoperative differentiation of ULMS from UL are often challenging because their symptoms and morphology resemble one another. Recent studies have shown frequent loss of alpha-thalassemia/mental retardation syndrome X-linked (ATRX) or death domain-associated protein (DAXX) expression in ULMS, and this is often associated with an alternative lengthening of telomeres (ALT) phenotype. Methods To investigate ATRX and DAXX expression and the presence of ALT in UL subtypes, immunohistochemical and telomere-specific fluorescence in situ hybridization analyses were performed. The study material consisted of 142 formalin-fixed, paraffin-embedded tissue samples representing various UL subtypes and 64 conventional ULs. Results A loss of ATRX or DAXX and/or ALT was detected in 6.3% of the histopathological UL subtype samples (9 of 142). Two patients whose ULs showed either ATRX loss or ALT were later diagnosed with a pulmonary smooth muscle tumor. Pulmonary tumors displayed molecular alterations found in the corresponding uterine tumors, which indicated metastasis to the lungs. All conventional ULs displayed normal ATRX, DAXX, and telomeres. Conclusions These results highlight the differences between conventional and histopathologically atypical ULs and indicate that some UL subtype tumors may harbor long-term malignant potential. Cancer 2018;124:4650-4656. (C) 2018 American Cancer Society.Peer reviewe

FGFR4 phosphorylates MST1 to confer breast cancer cells resistance to MST1/2-dependent apoptosis

Cancer cells balance with the equilibrium of cell death and growth to expand and metastasize. The activity of mammalian sterile20-like kinases (MST1/2) has been linked to apoptosis and tumor suppression via YAP/Hippo pathway-independent and -dependent mechanisms. Using a kinase substrate screen, we identified here MST1 and MST2 among the top substrates for fibroblast growth factor receptor 4 (FGFR4). In COS-1 cells, MST1 was phosphorylated at Y433 residue in an FGFR4 kinase activity-dependent manner, as assessed by mass spectrometry. Blockade of this phosphorylation by Y433F mutation induced MST1 activation, as indicated by increased threonine phosphorylation of MST1/2, and the downstream substrate MOB1, in FGFR4-overexpressing T47D and MDA-MB-231 breast cancer cells. Importantly, the specific knockdown or short-term inhibition of FGFR4 in endogenous models of human HER2(+) breast cancer cells likewise led to increased MST1/2 activation, in conjunction with enhanced MST1 nuclear localization and generation of N-terminal cleaved and autophosphorylated MST1. Unexpectedly, MST2 was also essential for this MST1/N activation and coincident apoptosis induction, although these two kinases, as well as YAP, were differentially regulated in the breast cancer models analyzed. Moreover, pharmacological FGFR4 inhibition specifically sensitized the HER2(+) MDA-MB-453 breast cancer cells, not only to HER2/EGFR and AKT/mTOR inhibitors, but also to clinically relevant apoptosis modulators. In TCGA cohort, FGFR4 overexpression correlated with abysmal HER2(+) breast carcinoma patient outcome. Therefore, our results uncover a clinically relevant, targetable mechanism of FGFR4 oncogenic activity via suppression of the stress-associated MST1/2-induced apoptosis machinery in tumor cells with prominent HER/ERBB and FGFR4 signaling-driven proliferation.Peer reviewe

Somatic MED12 Nonsense Mutation Escapes mRNA Decay and Reveals a Motif Required for Nuclear Entry

MED12 is a key component of the transcription-regulating Mediator complex. Specific missense and in-frame insertion/deletion mutations in exons 1 and 2 have been identified in uterine leiomyomas, breast tumors, and chronic lymphocytic leukemia. Here, we characterize the first MED12 5 end nonsense mutation (c.97G > T, p.E33X) identified in acute lymphoblastic leukemia and show that it escapes nonsense-mediated mRNA decay (NMD) by using an alternative translation initiation site. The resulting N-terminally truncated protein is unable to enter the nucleus due to the lack of identified nuclear localization signal (NLS). The absence of NLS prevents the mutant MED12 protein to be recognized by importin- and subsequent loading into the nuclear pore complex. Due to this mislocalization, all interactions between the MED12 mutant and other Mediator components are lost. Our findings provide new mechanistic insights into the MED12 functions and indicate that somatic nonsense mutations in early exons may avoid NMD. (C) 2017 Wiley Periodicals, Inc.Peer reviewe

Prevalence of RPGR-Mediated Retinal Dystrophy in an Unselected Cohort of Over 5000 Patients

Purpose: Comprehensive genetic testing for inherited retinal dystrophy (IRD) is challenged by difficult-to-sequence genomic regions, which are often mutational hotspots, such as RPGR ORF15. The purpose of this study was to evaluate the diagnostic contribution of RPGR variants in an unselected IRD patient cohort referred for testing in a clinical diagnostic laboratory. Methods: A total of 5201 consecutive patients were analyzed with a clinically validated next-generation sequencing (NGS)-based assay, including the difficult-to-sequence RPGR ORF15 region. Copy number variant (CNV) detection from NGS data was included. Variant interpretation was performed per the American College of Medical Genetics and Genomics guidelines. Results: A confirmed molecular diagnosis in RPGR was found in 4.5% of patients, 24.0% of whom were females. Variants in ORF15 accounted for 74% of the diagnoses; 29% of the diagnostic variants were in the most difficult-to-sequence central region of ORF15 (c.2470-3230). Truncating variants made up the majority (91%) of the diagnostic variants. CNVs explained 2% of the diagnostic cases, of which 80% were one- or two-exon deletions outside of ORF15. Conclusions: Our findings indicate that high-throughput, clinically validated NGS-based testing covering the difficult-to-sequence region of ORF15, in combination with high-resolution CNV detection, can help to maximize the diagnostic yield for patients with IRD. Translational Relevance: These results demonstrate an accurate and scalable method for the detection of RPGR-related variants, including the difficult-to-sequence ORF15 hotspot, which is relevant given current and emerging therapeutic opportunities.Peer reviewe

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Figure S7. A: Vimentin upregulation in UT-SCC-42B cell line was confirmed by immunoblotting using different shRNA constructs for PPFIA1. B: Downregulation of keratin 4, 10 and 13 expression levels in insoluble fraction of the UT-SCC-24B cells after liprin-α1 knockdown. C: Keratin 4 (red) and vimentin (green) localization in shScr and shPPFIA1 UT-SCC-24B cells. D: Western blot showed the level of knockdown of vimentin in breast cancer cells. Liprin-α1 protein levels did not alter significantly in control shScr and shVIM cells, but keratin 13 expression was decreased after vimentin knockdown. E: Immunofluorescence images for vimentin (green) and liprin-α1 (red) in MDA-MB-231 and Hs578T breast cancer cell lines and for vinculin (green) and liprin-α1 (red) in Hs578T breast cancer cell line after vimentin knockdown. (JPG 480 kb