Cell cycle-related kinase: a novel candidate oncogene in human glioblastoma.
BACKGROUND
Median survival for patients with glioblastoma multiforme, the most aggressive glioma, is only 12-15 months, despite multimodal treatment that includes surgery, chemotherapy, and radiotherapy. Thus, identification of genes that control the progression of glioblastoma multiforme is crucial for devising new therapies. We investigated the involvement of cell cycle-related kinase (CCRK), a novel protein kinase that is homologous to cyclin-dependent kinase 7, in glioblastoma multiforme carcinogenesis.


METHODS
We analyzed the expression levels of CCRK in 26 glioma patient samples (19 high-grade and seven low-grade) and normal brain by semiquantitative reverse transcription-polymerase chain reaction assays. CCRK expression was knocked down in human glioma U-373 MG and U-87 MG cells with small-interfering RNAs and short hairpin RNAs (siCCRK and shCCRK, respectively), and cell proliferation, cell cycle distribution, and cyclin-dependent kinase 2 (CDK2) phosphorylation were examined. A subcutaneous nude mouse xenograft model (n = 4 mice per group) was used to study the effect of CCRK knockdown and overexpression on tumorigenicity and growth of glioblastoma multiforme cells in vivo. All statistical tests were two-sided.


RESULTS
CCRK mRNA was elevated at least 1.5-fold and as much as 3.7-fold in 14 (74%) of 19 high-grade glioblastoma multiforme patient samples and in four (80%) of five glioma cell lines examined compared with normal brain tissue. Suppression of CCRK by siCCRK inhibited the proliferation of U-373 MG and U-87 MG glioblastoma cells in a time- and dose-dependent manner. The growth-inhibiting effect of siCCRK was mediated via G1- to S-phase cell cycle arrest and reduced CDK2 phosphorylation. CCRK knockdown statistically significantly suppressed glioma cell growth in vivo as indicated by the mean tumor volumes at week 6 after tumor cell injection (U-373-control = 1352 mm3, U-373-shCCRK = 294 mm3, difference = 1058 mm3, 95% confidence interval [CI] = 677 to 1439 mm3, P<.001; U-87-control = 1910 mm3, U-87-shCCRK = 552 mm3, difference = 1358 mm3, 95% CI = 977 to 1739 mm3, P<.001).


CONCLUSIONS
CCRK is a candidate oncogene in glioblastoma multiforme tumorigenesis.
Ng
Samuel S M
SS
Department of Chemistry, Open Laboratory of Chemical Biology, The University of Hong Kong, Pokfulam, Hong Kong, China.
Cheung
Yuen-Ting
YT
An
Xiao-Meng
XM
Chen
Yang Chao
YC
Li
Ming
M
Li
Gloria Hoi-Yee
GH
Cheung
William
W
Sze
Johnny
J
Lai
Lihui
L
Peng
Ying
Y
Xia
Harry H X
HH
Wong
Benjamin C Y
BC
Leung
Suet-Yi
SY
Xie
Dan
D
He
Ming-Liang
ML
Kung
Hsiang-Fu
HF
Lin
Marie C
MC
D000818:Animals; D001932:Brain Neoplasms / Q000201:enzymology / Q000235:genetics*; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D005260:Female; D005909:Glioblastoma / Q000201:enzymology / Q000235:genetics*; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D009857:Oncogenes; D010766:Phosphorylation; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D014183:Transplantation, Heterologous; D000095043:Cyclin-Dependent Kinase-Activating Kinase
D012333:RNA, Messenger; D034741:RNA, Small Interfering; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D000095043:Cyclin-Dependent Kinase-Activating Kinase