Expression of Aurora-B kinase and phosphorylated histone H3 in hepatocellular carcinoma.
BACKGROUND
Aurora-B, a chromosomal passenger protein forming a complex with INCENP (inner centromere protein) and survivin, regulates stable bipolar spindle-kinetochore attachment in mitosis and chromosome segregation and cytokinesis. It was recently documented that Aurora-B directly phosphorylated histone H3, not only at Ser10, but also at Ser28, which contributed to chromosome number instability and mitotic chromosome condensation. This study aimed at investigating the expression of Aurora-B kinase (Aurora-B) and phosphorylated histone H3 (H3-P) and their roles in hepatocellular carcinogenesis.


METHODS
The expressions of Aurora-B and H3-P were examined in hepatocellular carcinoma (HCC) by immunohistochemistry. A hepatoblastoma cell line, HepG2, was targeted and the isolation and characterization of alternative variants of Aurora-B were carried out. The Aurora encoding protein was detected in COS-7 transfected with different Aurora transcripts by Western blot. Finally, the expression of Aurora-B and its variant forms was examined in 17 HCCs by RT-PCR.


RESULTS
Immunohistochemically, Aurora-B was observed only in a few cases of HCC, while H3-P expression was more frequently detected in carcinoma foci than in non-carcinoma foci (p < 0.05). The isolation and characterization of two alternative variant forms of Aurora-B (termed Aurora-B1 and -B2) in the HepG2 cell line were successful. Aurora-B-transfected COS-7 cells expressed two different proteins, one of which was similar to the expression product of Aurora-B1 in size. Aurora-B transcripts were detected in 12 out of 17 (70.5%) HCC cases examined. Aurora-B2 was predominantly detected in 9 (52.9%) cases, while regular Aurora-B and Aurora-B1 were detected in 6 (35.2%) and 7 (41.1%) cases, respectively.


CONCLUSIONS
Aberrant expression of Aurora-B and H3-P plays a role in hepatocarcinogenesis. Alterative splicing of Aurora-B produces different sizes of proteins in HCC. Temporally altered phosphorylation of histone-H3 in the entire cell cycle may up-regulate the entry of HCC into the cell cycle to enhance their proliferation.
Sistayanarain
Anchalee
A
Molecular and Pathology, School of Medicine, University of Toyama, Sugitani 2630, Toyama, Japan.
Tsuneyama
Koichi
K
Zheng
Huachuan
H
Takahashi
Hiroyuki
H
Nomoto
Kazuhiro
K
Cheng
Chunmei
C
Murai
Yoshihiro
Y
Tanaka
Atsushi
A
Takano
Yasuo
Y
D000328:Adult; D017398:Alternative Splicing; D000818:Animals; D064107:Aurora Kinase B; D064127:Aurora Kinases; D001483:Base Sequence; D015153:Blotting, Western; D019556:COS Cells; D006528:Carcinoma, Hepatocellular / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D002454:Cell Differentiation; D002522:Chlorocebus aethiops; D005260:Female; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007124:Immunoenzyme Techniques; D008113:Liver Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012689:Sequence Homology, Nucleic Acid; D014162:Transfection; D014407:Tumor Cells, Cultured
D006657:Histones; D012333:RNA, Messenger; C576921:AURKB protein, human; D064107:Aurora Kinase B; D064127:Aurora Kinases; D017346:Protein Serine-Threonine Kinases