RESUMO
Chuvash polycythemia is an autosomal recessive form of erythrocytosis associated with a homozygous p.Arg200Trp mutation in the von Hippel-Lindau (VHL) gene. Since this discovery, additional VHL mutations have been identified in patients with congenital erythrocytosis, in a homozygous or compound-heterozygous state. VHL is a major tumor suppressor gene, mutations in which were first described in patients presenting with VHL disease, which is characterized by the development of highly vascularized tumors. Here, we identify a new VHL cryptic exon (termed E1') deep in intron 1 that is naturally expressed in many tissues. More importantly, we identify mutations in E1' in 7 families with erythrocytosis (1 homozygous case and 6 compound-heterozygous cases with a mutation in E1' in addition to a mutation in VHL coding sequences) and in 1 large family with typical VHL disease but without any alteration in the other VHL exons. In this study, we show that the mutations induced a dysregulation of VHL splicing with excessive retention of E1' and were associated with a downregulation of VHL protein expression. In addition, we demonstrate a pathogenic role for synonymous mutations in VHL exon 2 that altered splicing through E2-skipping in 5 families with erythrocytosis or VHL disease. In all the studied cases, the mutations differentially affected splicing, correlating with phenotype severity. This study demonstrates that cryptic exon retention and exon skipping are new VHL alterations and reveals a novel complex splicing regulation of the VHL gene. These findings open new avenues for diagnosis and research regarding the VHL-related hypoxia-signaling pathway.
Assuntos
Éxons , Predisposição Genética para Doença , Mutação , Policitemia/genética , Splicing de RNA , Proteína Supressora de Tumor Von Hippel-Lindau/genética , Doença de von Hippel-Lindau/genética , Adolescente , Adulto , Criança , Feminino , Heterozigoto , Humanos , Masculino , Pessoa de Meia-Idade , Linhagem , Policitemia/classificação , Policitemia/patologia , Adulto Jovem , Doença de von Hippel-Lindau/patologiaRESUMO
Myeloproliferative neoplasms (MPNs) are often characterized by JAK2 or calreticulin (CALR) mutations, indicating aberrant trafficking in pathogenesis. This study focuses on Mpl trafficking and Jak2 association using two model systems: human erythroleukemia cells (HEL; JAK2V617F) and K562 myeloid leukemia cells (JAK2WT). Consistent with a putative chaperone role for Jak2, Mpl and Jak2 associate on both intracellular and plasma membranes (shown by proximity ligation assay) and siRNA-mediated knockdown of Jak2 led to Mpl trapping in the endoplasmic reticulum (ER). Even in Jak2 sufficient cells, Mpl accumulates in punctate structures that partially colocalize with ER-tracker, the ER exit site marker (ERES) Sec31a, the autophagy marker LC3 and LAMP1. Mpl was fused to miniSOG, a genetically encoded tag for correlated light and electron microscopy. Results suggest that a fraction of Mpl is taken up into autophagic structures from the ER and routed to autolyososomes. Surface biotinylation shows that both immature and mature Mpl reach the cell surface; in K562 cells Mpl is also released in exosomes. Both forms rapidly internalize upon ligand addition, while recovery is primarily attributed to immature Mpl. Mpl appears to reach the plasma membrane via both conventional ER-Golgi and autolysosome secretory pathways, as well as recycling.
Assuntos
Membrana Celular/metabolismo , Receptores de Trombopoetina/metabolismo , Linhagem Celular Tumoral , Retículo Endoplasmático/metabolismo , Exossomos/metabolismo , Humanos , Janus Quinase 2/metabolismo , Células K562 , Proteínas de Membrana Lisossomal/metabolismo , Proteínas Associadas aos Microtúbulos/metabolismo , Transporte Proteico/fisiologia , Proteínas de Transporte Vesicular/metabolismoAssuntos
Recombinação Homóloga , Janus Quinase 2/genética , Processos Neoplásicos , Policitemia Vera/genética , Substituição de Aminoácidos , Cromossomos Humanos Par 9/genética , Cromossomos Humanos Par 9/metabolismo , Granulócitos/metabolismo , Humanos , Janus Quinase 2/metabolismo , Linfócitos/metabolismo , Modelos Genéticos , Mosaicismo , Mutação , Transtornos Mieloproliferativos/sangue , Transtornos Mieloproliferativos/genética , Transtornos Mieloproliferativos/metabolismo , Policitemia Vera/sangue , Policitemia Vera/metabolismo , Polimorfismo de Nucleotídeo Único , RNA Mensageiro/metabolismo , Trissomia/genética , Dissomia Uniparental/genética , Regulação para CimaRESUMO
Met is the receptor of hepatocyte growth factor (HGF), a cytoprotective cytokine. Disturbing the equilibrium between Met and its ligand may lead to inappropriate cell survival, accumulation of genetic abnormalities and eventually, malignancy. Abnormal activation of the HGF/Met axis is established in solid tumours and in chronic haematological malignancies, including myeloma, acute myeloid leukaemia, chronic myelogenous leukaemia (CML), and myeloproliferative neoplasms (MPNs). The molecular mechanisms potentially responsible for the abnormal activation of HGF/Met pathways are described and discussed. Importantly, inCML and in MPNs, the production of HGF is independent of Bcr-Abl and JAK2V617F, the main molecular markers of these diseases. In vitro studies showed that blocking HGF/Met function with neutralizing antibodies or Met inhibitors significantly impairs the growth of JAK2V617F-mutated cells. With personalised medicine and curative treatment in view, blocking activation of HGF/Met could be a useful addition in the treatment of CML and MPNs for those patients with high HGF/MET expression not controlled by current treatments (Bcr-Abl inhibitors in CML; phlebotomy, hydroxurea, JAK inhibitors in MPNs).