Liver kinase B1 regulates the centrosome via PLK1

K Werle,Y-L Li,C Lu,J Chen,R Cui,R-X Zhao,J Liang,Z-X Xu,Q He,H-G Xu

doi:10.1038/cddis.2014.135

Abstract

Liver kinase B1 (LKB1) is a tumor suppressor mutationally inactivated in Peutz–Jeghers syndrome (PJS) and various sporadic cancers. Although LKB1 encodes a kinase that possesses multiple functions, no individual hypothesis posed to date has convincingly explained how loss of LKB1 contributes to carcinogenesis. In this report we demonstrated that LKB1 maintains genomic stability through the regulation of centrosome duplication. We found that LKB1 colocalized with centrosomal proteins and was situated in the mitotic spindle pole. LKB1 deficiency-induced centrosome amplification was independent of AMP-activated protein kinase (AMPK), a well-defined substrate of LKB1. Cells lacking LKB1 exhibited an increase in phosphorylated and total Polo-like kinase 1 (PLK-1), NIMA-related kinase 2 (NEK2), and ninein-like protein (NLP). Overexpression of active PLK1 (T210D) reversed the inhibition of LKB1 on centrosome amplification. In contrast, depletion of PLK1 with siRNA or suppression of PLK1 kinase activity with BTO-1 (5-Cyano-7-nitro-2-benzothiazolecarboxamide-3-oxide) abrogated LKB1 deficiency-induced centrosome amplification. We further characterized that LKB1 phosphorylated and activated AMPK-related kinase 5 (NUAK1 or ARK5) that in turn increased the phosphorylation of MYPT1, enhanced the binding between MYPT1–PP1 and PLK1, and conferred an effective dephosphorylation of PLK1. More importantly, we noted that LKB1-deficient cells exhibited multiple nuclear abnormalities, such as mitotic delay, binuclear, polylobed, grape, large, and micronuclear. Immediate depletion of LKB1 resulted in the accumulation of multiploidy cells. Expression of LKB1 is reversely correlated with the levels of PLK1 in human cancer tissues. Thus, we have uncovered a novel function of LKB1 in the maintenance of genomic stability through the regulation of centrosome mediated by PLK1.

Highlights

It was shown in a genome-wide screen that downregulation of Liver kinase B1 (LKB1) causes spindle aberrations.[13]
We demonstrate that LKB1 locates to the centrosomes and the spindle poles during mitosis and that loss of LKB1 causes centrosome amplification and nuclear abnormalities
In a genome-wide screen of kinases required for cell cycle progress, Bettencourt-Dias et al.[13] found that LKB1 might participate in mitotic regulation, and depletion of LKB1 leads to multipolar spindles in the cells

Summary

Introduction

It was shown in a genome-wide screen that downregulation of LKB1 causes spindle aberrations.[13]. Aurora A is the best known kinase of PLK1.31 In a recent proteomic screen from mitotic cell extracts, Ji et al.[32] found that PLK1 is phosphorylated by p21-activated kinases 1 and 3 (PAK1/3) and mammalian Ste20-like kinase 1 (MST1) These kinases phosphorylate PLK1 at threonine 210 (T210), activating its kinase activity for substrates such as NIMA-related kinase 2 (NEK2) and nineinlike protein (NLP) that cause the centrioles to split,[27,33] and CDC25 to promote mitosis.[34] Even when one of these upstream kinases is blocked, phosphorylation of PLK1 at T210 still occurs, suggesting that PLK1 function is governed by multiple kinases to ensure proper advancement of mitosis.[32] PLK1 phosphorylation is crucial to promote mitosis, its dephosphorylation, which is carried out by the myosin phosphatase targeting subunit–protein phosphotase[1] complex (MYPT1–PP1), is imperative for mitotic exit.[35]

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Results

Conclusion