A novel interaction between kinase activities in regulation of cilia formation

Nicole Devaul,Rong Wang,Katerina Koloustroubis,Ann O Sperry

doi:10.1186/s12860-017-0149-5

Abstract

BackgroundThe primary cilium is an extension of the cell membrane that encloses a microtubule-based axoneme. Primary cilia are essential for transmission of environmental cues that determine cell fate. Disruption of primary cilia function is the molecular basis of numerous developmental disorders. Despite their biological importance, the mechanisms governing their assembly and disassembly are just beginning to be understood. Cilia growth and disassembly are essential events when cells exit and reenter into the cell cycle. The kinases never in mitosis-kinase 2 (Nek2) and Aurora A (AurA) act to depolymerize cilia when cells reenter the cell cycle from G0.ResultsCoexpression of either kinase with its kinase dead companion [AurA with kinase dead Nek2 (Nek2 KD) or Nek2 with kinase dead AurA (AurA KD)] had different effects on cilia depending on whether cilia are growing or shortening. AurA and Nek2 are individually able to shorten cilia when cilia are growing but both are required when cilia are being absorbed. The depolymerizing activity of each kinase is increased when coexpressed with the kinase dead version of the other kinase but only when cilia are assembling. Additionally, the two kinases act additively when cilia are assembling but not disassembling. Inhibition of AurA increases cilia number while inhibition of Nek2 significantly stimulates cilia length. The complex functional relationship between the two kinases reflects their physical interaction. Further, we identify a role for a PP1 binding protein, PPP1R42, in inhibiting Nek2 and increasing ciliation of ARPE-19 cells.ConclusionWe have uncovered a novel functional interaction between Nek2 and AurA that is dependent on the growth state of cilia. This differential interdependence reflects opposing regulation when cilia are growing or shortening. In addition to interaction between the kinases to regulate ciliation, the PP1 binding protein PPP1R42 directly inhibits Nek2 independent of PP1 indicating another level of regulation of this kinase. In summary, we demonstrate a complex interplay between Nek2 and AurA kinases in regulation of ciliation in ARPE-19 cells.

Highlights

The primary cilium is an extension of the cell membrane that encloses a microtubule-based axoneme
Previous studies have shown that Aurora A (AurA) and never in mitosiskinase 2 (Nek2) induce cilia depolymerization [11, 13]; we expected that cells transfected with the active kinases would be less ciliated than control
There was no significant difference in cilia length between active kinase and control (Fig. 1C, AurA vs control; Fig. 1D, Nek2 vs control)

Summary

Introduction

The primary cilium is an extension of the cell membrane that encloses a microtubule-based axoneme. Disruption of primary cilia function is the molecular basis of numerous developmental disorders. Despite their biological importance, the mechanisms governing their assembly and disassembly are just beginning to be understood. Cilia growth and disassembly are essential events when cells exit and reenter into the cell cycle. The kinases never in mitosiskinase 2 (Nek2) and Aurora A (AurA) act to depolymerize cilia when cells reenter the cell cycle from G0. Primary cilia are microtubule-based organelles that protrude from the cell membrane to receive and transduce environmental signals. All cells form primary cilia, Cilia display regulated growth and retraction when entering and exiting the cell cycle. Two important regulators of cilia absorption are the kinases Nek (NIMA related kinase 2) and AurA (Aurora A). Nek is a serine/threonine kinase that is localized to the distal portion of the mother centriole and functions in both cilia

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