Browsing by Author "Port, Sarah"

Nucleoporins build the nuclear pore complex (NPC), which, as sole gate for nuclear-cytoplasmic exchange, is of outmost importance for normal cell function. Defects in the process of nucleocytoplasmic transport or in its machinery have been frequently described in human diseases, such as cancer and neurodegenerative disorders, but only in a few cases of developmental disorders. Here we report biallelic mutations in the nucleoporin NUP88 as a novel cause of lethal fetal akinesia deformation sequence (FADS) in two families. FADS comprises a spectrum of clinically and genetically heterogeneous disorders with congenital malformations related to impaired fetal movement. We show that genetic disruption of nup88 in zebrafish results in pleiotropic developmental defects reminiscent of those seen in affected human fetuses, including locomotor defects as well as defects at neuromuscular junctions. Phenotypic alterations become visible at distinct developmental stages, both in affected human fetuses and in zebrafish, whereas early stages of development are apparently normal. The zebrafish phenotypes caused by nup88 deficiency are rescued by expressing wild-type Nup88 but not the disease-linked mutant forms of Nup88. Furthermore, using human and mouse cell lines as well as immunohistochemistry on fetal muscle tissue, we demonstrate that NUP88 depletion affects rapsyn, a key regulator of the muscle nicotinic acetylcholine receptor at the neuromuscular junction. Together, our studies provide the first characterization of NUP88 in vertebrate development, expand our understanding of the molecular events causing FADS, and suggest that variants in NUP88 should be investigated in cases of FADS.

A role of nucleoporins and of soluble transport factors in adenoviral genome import into the nucleus of infected cells in interphase has previously been established. The nuclear export receptor CRM1 promotes genome import, but its precise function is not known.

Background: The NUP98 and NUP214 nucleoporins (NUPs) are recurrently fused to heterologous proteins in leukemia. The resulting chimeric oncoproteins retain the NUP phenylalanine-glycine (FG) repeat motifs that mediate interaction with the nuclear export receptor Crm1. NUP fusion leukemias are characterized by HOXA gene upregulation; however, their molecular pathogenesis remains poorly understood. To investigate the role of Crm1 in mediating the leukemogenic properties of NUP chimeric proteins, we studied the SQSTM1-NUP214 fusion. Methods: We synthesized a SQSTM1-NUP214 fusion protein which retains only a short C-terminal portion of NUP214 containing FG motifs that mediate interaction with Crm1, and then introduced point mutations targeting these FG motifs (SQSTM1-NUP214FGmut). We compared the activity of these two fusion proteins using co-immunoprecipitation with CRM1, methylcellulose colony assays, murine transplantation, RT-qPCR, and chromatin immunoprecipitation. Results: We found that the ability of the SQSTM1-NUP214FGmut protein to interact with Crm1 was reduced by more than 50% compared with SQSTM1-NUP214. Further, mutation of FG motifs affected transforming potential: while SQSTM1-NUP214 conferred robust colony formation to transduced hematopoietic progenitors in a serial replating assay, the effect of SQSTM1-NUP214FGmut was greatly diminished. Moreover, SQSTM1-NUP214 caused myeloid leukemia in all transplanted mice (6/6), whereas none of the SQSTM1-NUP214FGmut reconstituted mice developed leukemia (0/7). These oncogenic effects coincided with the ability of SQSTM1-NUP214 and SQSTM1-NUP214FGmut to upregulate the expression of Hoxa and Meis1 genes in hematopoietic progenitors. Indeed, chromatin immunoprecipitation assays demonstrated that impairing the interaction of SQSTM1-NUP214 with Crm1 reduced binding of the fusion protein to Hoxa and Meis1 loci. Conclusions: These findings highlight the importance of Crm1 in mediating the leukemogenic properties of SQSTM1-NUP214, and suggest a conserved role of Crm1 in recruiting oncoproteins to their effector genes. Disclosures No relevant conflicts of interest to declare.