A non‐canonical function of Plk4 in centriolar satellite integrity and ciliogenesis through PCM 1 phosphorylation

Abstract

Centrioles are the major constituents of the animal centrosome, in which Plk4 kinase serves as a master regulator of the duplication cycle. Many eukaryotes also contain numerous peripheral particles known as centriolar satellites. While centriolar satellites aid centriole assembly and primary cilium formation, it is unknown whether Plk4 plays any regulatory roles in centriolar satellite integrity. Here we show that Plk4 is a critical determinant of centriolar satellite organisation. Plk4 depletion leads to the dispersion of centriolar satellites and perturbed ciliogenesis. Plk4 interacts with the satellite component PCM1, and its kinase activity is required for phosphorylation of the conserved S372. The nonphosphorylatable PCM1 mutant recapitulates phenotypes of Plk4 depletion, while the phosphomimetic mutant partially rescues the dispersed centriolar satellite patterns and ciliogenesis in cells depleted of PCM1. We show that S372 phosphorylation occurs during the G1 phase of the cell cycle and is important for PCM1 dimerisation and interaction with other satellite components. Our findings reveal that Plk4 is required for centriolar satellite function, which may underlie the ciliogenesis defects caused by Plk4 dysfunction.

Regulation of centriolar satellite integrity and its physiology

“…Importantly, this phenotype arises much earlier when the normal number of centrioles is still retained, and is observed even in G1-arrested cells when centrioles do not duplicate, indicating that satellite dispersion and centriolar duplication deficiency are separate and independent outcomes. Consistent with this notion, depletion of hSAS-6, a critical factor for centriole duplication [85], does not lead to satellite dispersion [117]. PCM1 was shown to be a phospho-protein and to interact with PLK4 by a proximity-dependent biotin identification method [23, 134–136].…”

“…Is there any converse regulation? A recent study showed that this is indeed the case [117]. PLK4 is regarded as a rate-limiting master regulator of centriole copy number control because centrioles fail to duplicate when PLK4 malfunctions but conversely undergo overamplification when PLK4 is overproduced [82, 118–120].…”

“…Surprisingly, PLK4 depletion or introduction of kinase-dead PLK4 to PLK4-depleted cells leads to the dispersion of centriolar satellite particles (PCM1, CEP290 and MSD1/SSX2IP) from the pericentriolar region [117]. Importantly, this phenotype arises much earlier when the normal number of centrioles is still retained, and is observed even in G1-arrested cells when centrioles do not duplicate, indicating that satellite dispersion and centriolar duplication deficiency are separate and independent outcomes.…”

“…S372 is conserved across a wide variety of eukaryotes. Because PLK4 binds to phosphorylated PCM1 in vivo, and PLK4 and PCM1 directly interact in vitro [117], PCM1 is likely an in vivo substrate of PLK4 (Fig. 5a).

Fig.

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The PLK4–STIL–SAS-6 module at the core of centriole duplication

“…PLK4 has been reported to phosphorylate several proteins implicated in centrosome biology, including its own centriolar recruitment factors Cep152 and Cep192 [56,58], PCM1 (a constituent of centriolar satellites) [89], GCP-6 (a component of the γ-tubulin ring complex) [90] and the FBXW5 F-Box protein implicated in SCF-mediated protein degradation of SAS-6 [91]. However, several of these studies are based exclusively on in vitro kinase reactions, and the significance and functional consequences of these phosphorylations in vivo remain to be fully understood.…”