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The Nek8 protein kinase, mutated in the human cystic kidney disease nephronophthisis, is both activated and degraded during ciliogenesis.

ABSTRACT: Mutations in the never-in-mitosis A-related kinase, Nek8, are associated with cystic kidney disease in both humans and mice, with Nek8 being the NPHP9 gene in the human juvenile cystic kidney disease, nephronophthisis. Human Nek8/NPHP9 localizes to centrosomes and the proximal region of cilia in dividing and ciliated cells, respectively. However, the regulation of Nek8 kinase activity, as well as its role in ciliogenesis, remains to be defined. Here, by establishing Nek8 kinase assays, we first demonstrate that the localization of Nek8 to centrosomes and cilia is dependent on both kinase activity and the C-terminal non-catalytic RCC1 domain. The kinase domain alone is active, but does not localize correctly, while the RCC1 domain localizes correctly and can be phosphorylated by Nek8. We propose that centrosome recruitment is mediated by the RCC1 domain, but requires a conformational change in the full-length protein that is promoted by autophosphorylation. Interestingly, three human NPHP9-associated mutants retain full kinase activity. However, only two of these, L330F and A497P, localize correctly, suggesting that the third mutant, H425Y, disrupts a centrosome targeting sequence in the RCC1 domain. Importantly, we find that induction of ciliogenesis upon cell cycle exit is accompanied by both activation and proteasomal degradation of Nek8, and that activation is dependent upon phosphorylation within the catalytic domain. Taken together, these findings reveal important insights into the mechanisms through which Nek8 activity and localization are regulated during ciliogenesis.

SUBMITTER: Zalli D

PROVIDER: S-EPMC3277313 | biostudies-literature | 2012 Mar

REPOSITORIES: biostudies-literature

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The Nek8 protein kinase, mutated in the human cystic kidney disease nephronophthisis, is both activated and degraded during ciliogenesis.

Zalli Detina D Bayliss Richard R Fry Andrew M AM

Human molecular genetics 20111121 5

Mutations in the never-in-mitosis A-related kinase, Nek8, are associated with cystic kidney disease in both humans and mice, with Nek8 being the NPHP9 gene in the human juvenile cystic kidney disease, nephronophthisis. Human Nek8/NPHP9 localizes to centrosomes and the proximal region of cilia in dividing and ciliated cells, respectively. However, the regulation of Nek8 kinase activity, as well as its role in ciliogenesis, remains to be defined. Here, by establishing Nek8 kinase assays, we first ...[more]

PMID: 22106379

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Project description:Ciliopathies are a group of genetic multi-systemic disorders related to dysfunction of the primary cilium, a sensory organelle present at the cell surface that regulates key signaling pathways during development and tissue homeostasis. In order to identify novel genes whose mutations would cause severe developmental ciliopathies, >500 patients/fetuses were analyzed by a targeted high throughput sequencing approach allowing exome sequencing of >1200 ciliary genes. NEK8/NPHP9 mutations were identified in five cases with severe overlapping phenotypes including renal cystic dysplasia/hypodysplasia, situs inversus, cardiopathy with hypertrophic septum and bile duct paucity. These cases highlight a genotype-phenotype correlation, with missense and nonsense mutations associated with hypodysplasia and enlarged cystic organs, respectively. Functional analyses of NEK8 mutations in patient fibroblasts and mIMCD3 cells showed that these mutations differentially affect ciliogenesis, proliferation/apoptosis/DNA damage response, as well as epithelial morphogenesis. Notably, missense mutations exacerbated some of the defects due to NEK8 loss of function, highlighting their likely gain-of-function effect. We also showed that NEK8 missense and loss-of-function mutations differentially affect the regulation of the main Hippo signaling effector, YAP, as well as the expression of its target genes in patient fibroblasts and renal cells. YAP imbalance was also observed in enlarged spheroids of Nek8-invalidated renal epithelial cells grown in 3D culture, as well as in cystic kidneys of Jck mice. Moreover, co-injection of nek8 MO with WT or mutated NEK8-GFP RNA in zebrafish embryos led to shortened dorsally curved body axis, similar to embryos injected with human YAP RNA. Finally, treatment with Verteporfin, an inhibitor of YAP transcriptional activity, partially rescued the 3D spheroid defects of Nek8-invalidated cells and the abnormalities of NEK8-overexpressing zebrafish embryos. Altogether, our study demonstrates that NEK8 human mutations cause major organ developmental defects due to altered ciliogenesis and cell differentiation/proliferation through deregulation of the Hippo pathway.

Dataset Information

The Nek8 protein kinase, mutated in the human cystic kidney disease nephronophthisis, is both activated and degraded during ciliogenesis.

Publications

The Nek8 protein kinase, mutated in the human cystic kidney disease nephronophthisis, is both activated and degraded during ciliogenesis.

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