title: Polo-like kinase 2 acting as a promoter in human tumor cells with an abundance of TAp73.
abstract: BACKGROUND
  TAp73, a member of the p53 tumor suppressor family, is frequently overexpressed in malignant tumors in humans. TAp73 abundance and phosphorylation modification result in variations in transcriptional activity. In a previous study, we found that the antitumor function of TAp73 was reactivated by dephosphorylation in head and neck squamous cell carcinomas. Polo-like kinase 2 (PLK2) displayed a close relationship with the p53 family in affecting the fate of cells. Herein, we investigate the hypothesis that PLK2 phosphorylates TAp73 and inhibits TAp73 function.
  
  
  METHODS
  Head and neck squamous cell carcinoma cell lines and osteosarcoma cell lines were used as natural models of the different expression levels of TAp73. Phosphorylation predictor software Scansite 3.0 and the predictor GPS-polo 1.0 were used to analyze the phosphorylation sites. Coimmunoprecipitation, phosphor-tag Western blot, metabolic labeling, and indirect immunofluorescence assays were used to determine the interactions between PLK2 and TAp73. TAp73 activity was assessed by Western blot and reverse transcription polymerase chain reaction, which we used to detect P21 and PUMA, both downstream genes of TAp73. The physiological effects of PLK2 cross talk with TAp73 on cell cycle progress and apoptosis were observed by flow cytometry and terminal deoxynucleotidyl transferase dUTP nick end labeling assays.
  
  
  RESULTS
  PLK2 binds to and phosphorylates TAp73. PLK2 phosphorylates TAp73 at residue Ser48 and prohibits TAp73 translocation to the nucleus. Additionally, PLK2 inhibition combined with a DNA-damaging drug upregulated p21 and PUMA mRNA expression to a greater extent than DNA-damaging drug treatment alone. Inhibiting PLK2 in TAp73-enriched cells strengthened the effects of the DNA-damaging drug on both G1 phase arrest and apoptosis. Pretreatment with TAp73-siRNA weakened these effects.
  
  
  CONCLUSIONS
  These findings reveal a novel PLK2 function (catalyzed phosphorylation of TAp73) which suppresses TAp73 functions. PLK2 promotes the survival of human tumor cells, a novel insight into the workings of malignant tumors characterized by TAp73 overexpression, and one that could speed the development of therapies.
authors.affiliation: Department of Orthopedics, Zhujiang Hospital of Southern Medical University, Guangzhou, Guangdong, People's Republic of China.
authors.forename: ZhengBo
authors.initials: Z
authors.lastname: Hu
authors.affiliation: Department of Orthopedics, Zhujiang Hospital of Southern Medical University, Guangzhou, Guangdong, People's Republic of China.
authors.forename: ZunYing
authors.initials: Z
authors.lastname: Xu
authors.affiliation: The State Key Laboratory of Respiratory Diseases, the First Affiliated Hospital of Guangzhou Medical University, Guangzhou, Guangdong, People's Republic of China.
authors.forename: XiaoHong
authors.initials: X
authors.lastname: Liao
authors.affiliation: Department of Orthopedics, Zhujiang Hospital of Southern Medical University, Guangzhou, Guangdong, People's Republic of China.
authors.forename: Xiao
authors.initials: X
authors.lastname: Yang
authors.affiliation: Department of Orthopedics, Zhujiang Hospital of Southern Medical University, Guangzhou, Guangdong, People's Republic of China.
authors.forename: Cao
authors.initials: C
authors.lastname: Dong
authors.affiliation: Department of Orthopedics and Traumatology, The University of Hong Kong, Hong Kong, SAR, People's Republic of China.
authors.forename: KuaDi
authors.initials: K
authors.lastname: Luk
authors.affiliation: Department of Orthopedics, Zhujiang Hospital of Southern Medical University, Guangzhou, Guangdong, People's Republic of China.
authors.forename: AnMin
authors.initials: A
authors.lastname: Jin
authors.affiliation: Department of Orthopedics, the Third Affiliated Hospital of the Southern Medical University, Guangzhou, Guangdong, People's Republic of China ; Academy of Orthopedics, Guangdong Province, People's Republic of China.
authors.forename: Hai
authors.initials: H
authors.lastname: Lu
keywords: DNA damaging reagent; PLK2; TAp73; antitumor therapy; phosphorylation