Functional Alterations in Ciliogenesis-Associated Kinase 1 (CILK1) that Result from Mutations Linked to Juvenile Myoclonic Epilepsy.

Eric J Wang,Zheng Fu,Casey D Gailey,David L Brautigan

doi:10.3390/cells9030694

Abstract

Ciliopathies are a group of human genetic disorders associated with mutations that give rise to the dysfunction of primary cilia. Ciliogenesis-associated kinase 1 (CILK1), formerly known as intestinal cell kinase (ICK), is a conserved serine and threonine kinase that restricts primary (non-motile) cilia formation and length. Mutations in CILK1 are associated with ciliopathies and are also linked to juvenile myoclonic epilepsy (JME). However, the effects of the JME-related mutations in CILK1 on kinase activity and CILK1 function are unknown. Here, we report that JME pathogenic mutations in the CILK1 N-terminal kinase domain abolish kinase activity, evidenced by the loss of phosphorylation of kinesin family member 3A (KIF3A) at Thr672, while JME mutations in the C-terminal non-catalytic domain (CTD) have little effect on KIF3A phosphorylation. Although CILK1 variants in the CTD retain catalytic activity, they nonetheless lose the ability to restrict cilia length and also gain function in promoting ciliogenesis. We show that wild type CILK1 predominantly localizes to the base of the primary cilium; in contrast, JME variants of CILK1 are distributed along the entire axoneme of the primary cilium. These results demonstrate that JME pathogenic mutations perturb CILK1 function and intracellular localization. These CILK1 variants affect the primary cilium, independent of CILK1 phosphorylation of KIF3A. Our findings suggest that CILK1 mutations linked to JME result in alterations of primary cilia formation and homeostasis.

Highlights

The primary cilium is a single diminutive protrusion on the apical surface of almost all vertebrate cells that is enriched in receptors, ion channels, second messengers, and various signaling pathways.It employs these factors to sense and transduce environmental and hormonal signals to regulate intracellular processes and control cell behaviors [1]
Ciliogenesis-associated kinase 1 (CILK1) variants found in juvenile myoclonic epilepsy (JME) retain this ability to restrict cilia length
Given the variation in cilia length of control cells associated with each variant, we presented the above data in Figure S3, showing the impact of CILK1 variants on cilia length relative to each individual control

Summary

Introduction

The primary cilium is a single diminutive protrusion on the apical surface of almost all vertebrate cells that is enriched in receptors, ion channels, second messengers, and various signaling pathways. It employs these factors to sense and transduce environmental and hormonal signals to regulate intracellular processes and control cell behaviors [1]. Defects in primary cilium function are linked to human diseases collectively called ciliopathies [2]. The mechanisms underlying the pathological phenotypes associated with ciliopathies are still poorly understood. Ciliogenesis-associated kinase 1 (CILK1) [3], formerly known as intestinal cell kinase (ICK)

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Results

Conclusion