Oncogenic and tumor suppressive roles of polo‐like kinases in human hepatocellular carcinoma

Polo‐like kinase (PLK) proteins play critical roles in the control of cell cycle progression, either favoring or inhibiting cell proliferation, and in DNA damage response. Although either overexpression or down‐regulation of PLK proteins occurs frequently in various cancer types, no comprehensive analysis on their function in human hepatocellular carcinoma (HCC) has been performed to date. In the present study, we define roles for PLK1, PLK2, PLK3, and PLK4 during hepatocarcinogenesis. Levels of PLK1, as assessed by means of real‐time reverse‐transcription PCR and western blot analysis, were progressively increased from nonneoplastic surrounding liver tissues to HCC, reaching the highest expression in tumors with poorer outcome (as defined by the length of patients' survival) compared with normal livers. In sharp contrast, PLK2, PLK3, and PLK4 messenger RNA and protein expression gradually declined from nontumorous liver to HCC, with the lowest levels being detected in HCC with shorter survival. In liver tumors, PLK2‐4 down‐regulation was paralleled by promoter hypermethylation and/or loss of heterozygosity at the PLK2‐4 loci. Subsequent functional studies revealed that PLK1 inhibition led to suppression of cell growth in vitro, whereas opposite effects followed PLK2‐4 silencing in HCC cell lines. In particular, suppression of PLK1 resulted in a block in the G2/M phase of the cell cycle and in massive apoptosis of HCC cells in vitro regardless of p53 status. Conclusion: PLK1‐4 proteins are aberrantly regulated and possess different roles in human HCC, with PLK1 acting as an oncogene and PLK2‐4 being presumably tumor suppressor genes. Thus, therapeutic approaches aimed at inactivating PLK1 and/or reactivating PLK2‐4 might be highly useful in the treatment of human liver cancer. (HEPATOLOGY 2010.)

[1]  S. Thorgeirsson,et al.  Molecular pathogenesis of human hepatocellular carcinoma , 2002, Nature Genetics.

[2]  J. Dennis,et al.  Late mitotic failure in mice lacking Sak, a polo-like kinase , 2001, Current Biology.

[3]  Erich A. Nigg,et al.  Polo-like kinases and the orchestration of cell division , 2004, Nature Reviews Molecular Cell Biology.

[4]  Hao Li,et al.  Plk1-dependent phosphorylation of FoxM1 regulates a transcriptional programme required for mitotic progression , 2008, Nature Cell Biology.

[5]  Long-Cheng Li,et al.  MethPrimer: designing primers for methylation PCRs , 2002, Bioinform..

[6]  Q. Cai,et al.  Aberrant Polo-Like Kinase 1-Cdc25A Pathway in Metastatic Hepatocellular Carcinoma , 2008, Clinical Cancer Research.

[7]  S. Thorgeirsson,et al.  Ubiquitous activation of Ras and Jak/Stat pathways in human HCC. , 2006, Gastroenterology.

[8]  Christopher J. Wilkinson,et al.  The Polo kinase Plk4 functions in centriole duplication , 2005, Nature Cell Biology.

[9]  D. Longo,et al.  Expression and phosphorylation of fibroblast-growth-factor-inducible kinase (Fnk) during cell-cycle progression. , 1998, The Biochemical journal.

[10]  D. Longo,et al.  Malignant transformation of mammalian cells initiated by constitutive expression of the polo-like kinase. , 1997, Biochemical and biophysical research communications.

[11]  S. Thorgeirsson,et al.  Classification and prediction of survival in hepatocellular carcinoma by gene expression profiling , 2004, Hepatology.

[12]  U. Hoffmann‐Rohrer,et al.  Polo-like Kinase-2 Is Required for Centriole Duplication in Mammalian Cells , 2004, Current Biology.

[13]  Michele Pagano,et al.  The Cdc14B-Cdh1-Plk1 Axis Controls the G2 DNA-Damage-Response Checkpoint , 2008, Cell.

[14]  B. Carr,et al.  Multiple genetic alterations, 4q28, a new suppressor region, and potential gender differences in human hepatocellular carcinoma , 1999, Hepatology.

[15]  Z. Darżynkiewicz,et al.  Cell Cycle Arrest and Apoptosis Induced by Human Polo-Like Kinase 3 Is Mediated through Perturbation of Microtubule Integrity , 2002, Molecular and Cellular Biology.

[16]  Xiaoqi Liu,et al.  Polo-like kinase (Plk)1 depletion induces apoptosis in cancer cells , 2003, Proceedings of the National Academy of Sciences of the United States of America.

[17]  C. McGowan,et al.  Mammalian Polo-like kinase 3 (Plk3) is a multifunctional protein involved in stress response pathways , 2002, Oncogene.

[18]  Michael B Yaffe,et al.  Structure and function of Polo-like kinases , 2005, Oncogene.

[19]  Xin Xu,et al.  Overexpression of PLK1 is associated with poor survival by inhibiting apoptosis via enhancement of survivin level in esophageal squamous cell carcinoma , 2009, International journal of cancer.

[20]  R. Erikson,et al.  Polo-like kinase 3 is required for entry into S phase , 2007, Proceedings of the National Academy of Sciences.

[21]  J. Dennis,et al.  Sak/Plk4 and mitotic fidelity , 2005, Oncogene.

[22]  S. Loibl,et al.  Downregulation of human polo-like kinase activity by antisense oligonucleotides induces growth inhibition in cancer cells , 2002, Oncogene.

[23]  Ingrid Hoffmann,et al.  Transcriptional silencing of Polo-like kinase 2 (SNK/PLK2) is a frequent event in B-cell malignancies. , 2006, Blood.

[24]  H. El‐Serag,et al.  Hepatocellular carcinoma: epidemiology and molecular carcinogenesis. , 2007, Gastroenterology.

[25]  K. Kaestner,et al.  The mouse Forkhead Box m1 transcription factor is essential for hepatoblast mitosis and development of intrahepatic bile ducts and vessels during liver morphogenesis. , 2004, Developmental biology.

[26]  J. Bruix,et al.  Molecular targeted therapies in hepatocellular carcinoma , 2008, Hepatology.

[27]  W. Dai,et al.  Polo-like kinase 3 functions as a tumor suppressor and is a negative regulator of hypoxia-inducible factor-1 alpha under hypoxic conditions. , 2008, Cancer research.

[28]  R. Knight,et al.  p73-mediated transcriptional activity is negatively regulated by Polo-like kinase 1 , 2008, Cell cycle.

[29]  J. Winkles,et al.  Differential regulation of polo-like kinase 1, 2, 3, and 4 gene expression in mammalian cells and tissues , 2005, Oncogene.

[30]  D. Calvisi,et al.  Forkhead box M1B is a determinant of rat susceptibility to hepatocarcinogenesis and sustains ERK activity in human HCC , 2009, Gut.

[31]  H. Otto,et al.  Flow cytometric DNA analysis and chromosomal aberrations in malignant glioblastomas. , 1999, Cancer letters.

[32]  S. Thorgeirsson,et al.  Disruption of beta-catenin pathway or genomic instability define two distinct categories of liver cancer in transgenic mice. , 2004, Gastroenterology.

[33]  A. Nakagawara,et al.  Inhibitory Role of Plk1 in the Regulation of p73-dependent Apoptosis through Physical Interaction and Phosphorylation* , 2008, Journal of Biological Chemistry.

[34]  J. Dennis,et al.  Plk4 haploinsufficiency causes mitotic infidelity and carcinogenesis , 2005, Nature Genetics.

[35]  Ronald A. DePinho,et al.  Hepatocellular carcinoma pathogenesis: from genes to environment , 2006, Nature Reviews Cancer.

[36]  K. Strebhardt,et al.  Polo-like kinases and oncogenesis , 2005, Oncogene.

[37]  K. Kinzler,et al.  A panel of isogenic human cancer cells suggests a therapeutic approach for cancers with inactivated p53 , 2009, Proceedings of the National Academy of Sciences.

[38]  Michael J. Emanuele,et al.  A Genome-wide RNAi Screen Identifies Multiple Synthetic Lethal Interactions with the Ras Oncogene , 2009, Cell.

[39]  Z. Darżynkiewicz,et al.  Polo-like kinase 3 is Golgi localized and involved in regulating Golgi fragmentation during the cell cycle. , 2004, Experimental cell research.

[40]  Akira Nakagawara,et al.  Polo-like Kinase 1 (Plk1) Inhibits p53 Function by Physical Interaction and Phosphorylation* , 2004, Journal of Biological Chemistry.

[41]  M. Rudnicki,et al.  Simplified mammalian DNA isolation procedure. , 1991, Nucleic acids research.