Identification of overexpressed genes in hepatocellular carcinoma, with special
reference to ubiquitin-conjugating enzyme E2C gene expression
Keisuke Ieta1,2, Eiki Ojima1, Fumiaki Tanaka1, Yoshito Nakamura1, Naotsugu Haraguchi1, Koshi Mimori1, Hiroshi Inoue1,
Hiroyuki Kuwano2and Masaki Mori1*
1Department of Surgery and Molecular Oncology, Medical Institute of Bioregulation, Kyushu University, 4546 Tsurumihara,
Beppu 874-0838, Japan
2Department of General Surgical Science, Graduate School of Medicine, Gunma University, 3-39-22 Showa-machi,
Maebashi, Gunma, Japan
This study consisted of 2 aims: (i) to determine genes associated
with hepatocellular carcinoma (HCC) by microarray analysis;
and (ii) to evaluate the clinicopathological significance of human
ubiquitin-conjugating enzyme E2C (Ube2c) found to be overex-
pressed in HCC from microarray analysis. Laser microdissection
and cDNA-microarray were performed to identify genes associ-
ated with HCC. We then focused on the Ube2c gene. Using real-
time quantitative reverse transcription-polymerase chain reaction
(RT-PCR), Ube2c expression status and clinicopathological signifi-
cance were studied in 65 clinical HCC samples. A number of genes
upregulated in HCC cells compared to noncancerous liver cells
were identified, one of which was the Ube2c gene. Ube2c gene
expression in the cancer tissue was higher than in the correspond-
ing noncancerous tissue in 62 of the 65 cases (95.4%, p < 0.01).
Tumors with high Ube2c expression showed higher frequencies of
tumor invasion to capsular formation (fc-inf), invasion to portal
vein (vp) and tumor de-differentiation (p < 0.05). Patients with
high Ube2c expression also showed significantly worse disease-free
survival rates than those with low Ube2c expression (p < 0.01). In
addition, Ube2c expression was found to be an independent prog-
nostic factor for disease-free survival rate in multivariate analysis.
We identified differentially expressed genes between HCC and
normal liver tissues. Of those, the Ube2c gene appeared to be asso-
ciated with HCC progression, and may be useful as a prognostic
indicator for HCC patients.
' 2007 Wiley-Liss, Inc.
Key words: hepatocellular carcinoma; microarray; laser microdissection
(LMD); ubiquitin-conjugating enzyme E2C (Ube2c)
Hepatocellular carcinoma (HCC) is one of the most common
cancers in Japan, and its prevalence is increasing in America.
Most Japanese HCC cases develop from liver cirrhosis that is
almost entirely due to chronic hepatitis C or B.1–3Although recent
advances in molecular biology have elucidated the developmental
pathway of HCC from liver cirrhosis, few studies have determined
the differences in gene expression profiles between HCC and nor-
mal liver tissues. Therefore, we analyzed for differentially
expressed genes between cancerous tissues from HCC patients
and noncancerous liver tissues without liver cirrhosis from
patients with metastatic liver tumors using laser microdissection
(LMD) and cDNA-microarray. As a result, we detected 123 genes
that were overexpressed by more than 2-fold in HCC compared to
normal liver in at least 4 of the 6 samples examined. In the past,
our group has worked on the ubiquitination system in cancer cells.
For example, S-phase kinase-associated protein 2 (Skp2), a mem-
ber of the F-box family of substrate-recognition subunits of Skp1-
Cullin-F-box ubiquitin-protein ligase complexes, is necessary for
p27 ubiquitination and degradation. We reported that Skp2 gene
overexpression appeared to act as a prognostic factor for gastric
cancer and breast cancer.4–6Because of this interest, of the genes
observed to be upregulated in HCC, we decided to focus on the
Ube2c gene due to its involvement in the ubiquitination pathway.
The Ube2c gene, located on chromosome 20q13, belongs to the
E2 gene family and codes for a 19.6 kDa protein involved in ubiq-
uitin-dependent proteolysis. Rape and Kirschner showed that
cyclin A degradation was highly sensitive to the concentration of
Ube2c, and self-degradation of Ube2c is an autonomous sensor of
mitotic completion and provides the molecular switch that allows
cells to proceed from DNA segregation and cell division to a new
round of DNA duplication.7,8Ube2c has also been reported to be
highly expressed in various types of cancers.9–13However, the
relationship between Ube2c expression and clinicopathological
factors in HCC has not yet been investigated.
In the present study, we report the identification of overex-
pressed genes in HCC by LMD and cDNA-microarray analysis,
and then examine the clinicopathological significance of the
Ube2c gene, detected as an overexpressed gene in HCC patients.
Material and methods
Sixty-five patients with HCC were enrolled into this study. All
patients underwent resection of the primary tumor at the Kyushu
University Hospital at Beppu and affiliated hospitals between
2001 and 2003. Resected tumor and paired nontumor tissue speci-
mens were immediately cut from the resected liver and placed in
RNA Layter (TaKaRa, Japan) or embedded in Tissue Tek OCT
medium (Sakura, Tokyo, Japan), frozen in liquid nitrogen and
kept at 280?C until RNA extraction. Written informed consent
was obtained from all patients. The follow-up period ranged from
0.1 to 4.3 years with a median of 2.5 years.
Identification of overexpressed genes in HCC
Samples. For the identification of overexpressed genes in
HCC, 6 randomly selected HCC cases were used (hepatitis B virus
(HBV) (1): 2 cases, hepatitis C virus (HCV) (1): 2 cases, HBV
(2) HCV (2): 2 cases). As a control, the samples of noncancerous
liver tissues were obtained from another 6 cases. These 6 were the
Grant sponsors: CREST, Japan Science and Technology Agency (JST);
Japan Society for the Promotion of Science (JSPS); Grant numbers:
17109013, 17591411, 17591413,
18790964; Grant sponsor: The Ministry of Education, Culture, Sports, Sci-
ence and Technology (MEXT); Grant number: 18015039; Grant sponsor:
Third Term Comprehensive Ten-year Strategy for Cancer Control; Grant
*Correspondence to: Department of Surgery and Molecular Oncology,
Medical Institute of Bioregulation, Kyushu University, 4546 Tsurumihara,
Beppu 874-0838, Japan. Fax: 181-977-27-1650/1651.
Received 11 November 2006; Accepted after revision 27 December
Published online 12 March 2007 in Wiley InterScience (www.interscience.
This article contains supplementary material available via the Internet at
Abbreviations: GAPDH, glyceraldehydes-3-phosphate dehydrogenase;
HBV, hepatitis B virus; HCC, hepatocellular carcinoma; HCV, hepatitis C
virus; LMD, laser microdissection; PCR, polymerase chain reaction; RT-
PCR, reverse transcription-polymerase chain reaction; Ube2c, ubiquitin-
conjugating enzyme E2C.
Int. J. Cancer: 121, 33–38 (2007)
' 2007 Wiley-Liss, Inc.
Publication of the International Union Against Cancer
patients with metastatic liver tumor, and the liver showed normal
appearance without cirrhosis or infection with HCV or HBV.
Laser microdissection and RNA extraction. Cancer tissues
were microdissected using the LMD system (Leica Laser Micro-
dissection System, Leica Microsystems, Wetzlar, Germany) as
previously described.14Total RNA was extracted using an Rneasy
Mini Kit (Qiagen, Hilden, Germany) according to the manufac-
turer’s instructions. Total RNA from noncancerous samples was
obtained from 6 normal liver samples. Purity and concentration of
the RNA samples were determined with a Nano Drop (Nano Drop
Technologies, Wilmington) and Agilent 2100 Bioanalyzer (Agi-
lent Technologies, Palo Alto) as previously described.15
cDNA-microarray. T7-based RNA amplification was per-
formed using the Low RNA Input Fluorescent Linear Amplifica-
tion Kit (Agilent Technologies, USA). Total RNA (100 ng) was
reverse transcribed to cDNA using MMLV-RT and oligo dT pri-
mers, and used as a template for in vitro transcription reactions in
the presence of Cyanine labeled CTP (NEN Life Science, Boston,
MA) and T7 RNA polymerase. cRNA from noncancerous tissues
was labeled with Cyanine 3-CTP (Cy3), while cancer tissue cRNA
was labeled with Cyanine 5-CTP (Cy5). After purification using
an Rneasy Mini Kit, aliquots of the amplified cRNA were vali-
dated on an Agilent 2100 Bioanalyzer. The Cy3 and Cy5 labeled
cRNA were mixed and hybridized to a cDNA-microarray (Agilent
Human1:12814genes, Agilent Technologies, USA). A list of genes
on this cDNA microarray is available from http://www.agilent.-
com/chem/genelists. Scanning of the array slides was performed
using an Agilent dual laser DNA microarray scanner (Agilent
Data analysis. The intensity of each hybridization signal was
evaluated using Feature Extraction software (Agilent Technolo-
gies, USA). The common logarithm of the Cy5/Cy3 ratio for each
sample was calculated by averaging the spots. A cutoff value for
expression level was automatically calculated according to the
background fluctuation. Normalization of expression levels was
performed using LOWESS (locally weighted linear regression
curve fit) normalization.16Rosetta Laminator system version 2.0
(Rosetta Biosoftware, Kirkland, USA) was used to analyze gene
expression data. Candidate genes which fulfilled the following cri-
teria were selected: the fold changes were >2.0, and the p value
was <0.01. Moreover, within the selected genes that met these cri-
teria, genes that were upregulated in 4 or more samples (6 total
samples) were analyzed.
Evaluation of Ube2c gene expression
Clinical samples and cell lines. For evaluation of Ube2c gene
expression, all 65 tumors and nontumor samples, as described
above, were used. Human HCC cell lines (HuH-7, Hep-G2, Hep-
3B) were provided by the Cell Resource Center of Biomedical
Research, Institute of Development, Aging and Cancer (Tohoku
University, Sendai, Japan) and maintained in RPMI 1640 medium
or DMEM containing 10% fetal bovine serum (FBS) and antibiot-
ics at 37?C in a 5% humidified CO2atmosphere.
Oligonucleotide primers for Ube2c gene amplification by
RT-PCR. Total RNA was extracted from each clinical sample
and cDNA synthesized from 8.0 lg total RNA as previously
Ube2c-specific oligonucleotide primers were designed to give a
165 bp PCR product: sense primer 50-GGATTTCTGCCTTCCCT-
GAA-30; antisense primer 50-GATAGCAGGGCGTGAGGAAC-
30.12Primers were also designed for glyceraldehyde 3-phosphate
dehydrogenase (GAPDH) (270 bp): sense primer 50-TTG-
GTATCGTGGAAGGACTCA-30; antisense primer 50-TGTCAT-
CATATTTGGCAGGTT-30. To avoid amplification of contami-
nating genomic DNA, the primers spanned more than 2 exons.
Amplification was performed for 29 cycles (22 cycles for
GAPDH) of 1 min at 95?C, 1 min at 60?C (56?C for GAPDH) and
1 min at 72?C. An 8.0 ll aliquot of each PCR-amplified DNA was
electrophoresed on 2% agarose gels containing ethidium bromide.
Real-time quantitative RT-PCR. PCR amplification for quanti-
fication of Ube2c and GAPDH mRNA in 65 clinical samples was
performed using the LightCycler system (Roche Applied Science,
IN) and the LightCycler-FastStart DNA Master SYBR Green I kit
(Roche Applied Science, IN) as previously described.17Amplifi-
cation conditions consisted of initial denaturation at 95?C for
10 min, followed by 40 cycles of denaturation at 95?C for 10 s,
annealing at 64?C (60?C for GAPDH) for 10 s and elongation at
72?C for 10 s. Melting curve analysis and electrophoresis on 2%
agarose gels were performed to ensure that the expected PCR
products were generated. To quantitate specific mRNA in the sam-
ples, a standard curve was produced for each run based on 3 points
from diluted HuH-7 cDNA. Relative Ube2c expression levels
were then obtained by normalizing the amount of Ube2c mRNA
divided by that of GAPDH mRNA as an endogenous control in
Western blot analysis. Total protein was extracted from 4 rep-
resentative pairs of samples and cell lines using protein extrac-
tion solution (PRO-PREP, iNtRON Biotecnology, Korea). Ali-
quots of total protein (60 lg for clinical samples or 20 lg for cell
lines) were electrophoresed in 12.5% concentrated READY
GELS J (Bio-Rad Laboratories, Japan) and then electroblotted
onto pure nitrocellulose membranes (Trans-Blot Transfer Me-
dium; Bio-Rad Laboratories, Japan) at 0.2 A for 120 min at 4?C.
Ube2c protein was detected using goat polyclonal antibody
(AB3935, Abcam, USA) diluted 1:200. Ube2c protein levels
were normalized to the level of b-actin protein (Cytoskelton,
Denver, CO) diluted 1:1,000. Blots were developed with horse-
radish peroxidase-linked anti-goat immunoglobulin (Promega,
Madison, WI) diluted 1:1,000. ECL Detection Reagents (Amer-
sham Biosciences, Piscataway, NJ) were used to detect antigen-
Immunohistochemistry. Immunohistochemical studies of Ube2c
were performed on surgical specimens from representative HCC
patients. Formalin-fixed, paraffin-embedded tissues were deparaffi-
nized, blocked, incubated with specific antibodies overnight at 4?C,
and detected using ENVISION reagents (ENVISION1 Dual Link/
HRP, Dako Cytomation, Denmark). All sections were counter-
stained with hematoxylin. Primary goat polyclonal anti-Ube2c anti-
body (AB3935, Abcam, USA) was used at a dilution of 1:200.
Ube2c RNA interference. Ube2c-specific siRNA (SilencerTM
Predesigned siRNA) and negative control siRNA (SilencerTM
Negative Control siRNA) were purchased from Ambion, USA.
Logarithmic growth-phase Hep3B cells were seeded at 1.5 3 105
or 2 3 103cells/well in a final volume of 2 ml or 100 ll, respec-
tively, in 6 or 96 well flat bottom microtitre plates, respectively,
and then cultured overnight to allow adherence. siRNA-Lipofecta-
mineTM2000 complexes were then added to each well as previ-
ously described,18and in vitro proliferation assay were performed
after 48 hr incubation from siRNA addition.
In vitro proliferation assay. Proliferation was determined by
(MTT) assay (Roche Diagnostics Corp., GmbH). After 48 hr incu-
bation from siRNA addition, cells were further cultured for 0–
96 hr. After 0–96 hr culture, spectrophotometrical absorbance of
the samples was measured as previously described.18Each inde-
pendent experiment was performed 3 times.
Statistical analysis. For continuous variables, data were
expressed as the means 6 SD. Differences between groups were
estimated using Student’s t test, v2 test, and repeated measures
ANOVA analysis. We applied the Student’s t-test for data in nor-
mal distribution and the nonparametric Wilcoxon/Kruskal–Wallis
tests for data without normal distribution. Overall survival curves
and disease-free survival curves were plotted according to the
Kaplan-Meier method, and measured from the day of surgery,
with the log-rank test applied for comparisons. Variables with a
value of p < 0.15 by univariate analysis were used in subsequent
multivariate analyses based on Cox’s proportional hazards model.
All differences were deemed significant at the level of p < 0.05.
IETA ET AL.
Statistical analyses were performed using the JMP 5 for Windows
software package (SAS Institute, Cary, NC).
Identification of overexpressed genes in HCC
Using a human cDNA-microarray, we determined differentially
expressed genes between HCC and noncancerous liver cells. We
identified 123 upregulated genes in the cancer cells compared to
the noncancerous cells (Supplementary 1). These genes were over-
expressed more than 2-fold in at least 4 of 6 cases, and included
genes previously reported to be associated with HCC, such as
PEG10.19–28Genes involved in cell cycle regulation or cell adhe-
sion, as well as growth factors and proteinases were also overex-
pressed and so could be considered as candidate cancer-related
genes. One of the overexpressed genes was Ube2c, associated
Evaluation of Ube2c gene expression
Expression of Ube2c mRNA in cell lines and clinical tissue
specimens. Ube2c mRNA expression in cell lines was examined
by reverse transcription-polymerase chain reaction (RT-PCR) and
revealed that all 3 cell lines tested, HuH-7, Hep-G2 and Hep-3B,
highly expressed Ube2c mRNA. Ube2c mRNA expression in can-
cerous and noncancerous tissues of HCC patients was examined
by RT-PCR and real-time quantitative PCR, with quantified values
used to calculate Ube2c/GAPDH expression ratios. Results indi-
cated that Ube2c mRNA expression levels were higher in cancer
tissues (0.074 6 0.066) than in noncancerous tissues (0.012 6
0.014) in 62 of the 65 cases (95.4%). This resulted in a significant
difference in mRNA expression level between cancer and normal
tissues (p < 0.01) (Figs. 1a and 1b). We classified the 65 HCC
cases into 2 groups according to median Ube2c mRNA expression
level in tumor tissues, as determined by quantitative RT-PCR, to
give high (n 5 33) and low (n 5 32) expression groups.
The clinicopathological significance of Ube2c mRNA expres-
sion in HCC. Clinicopathological features were analyzed in rela-
tion to Ube2c expression status (Table I). The incidence of tumor
invasion to capsular formation (fc-inf) was significantly higher (p
< 0.05) in the high expression group (23 of 33 fc-inf positive,
69.7%) than in the low expression group (13 of 32 fc-inf positive,
40.6%). Likewise, the incidence of invasion to portal vein (vp)
was higher (p < 0.05) in the high expression group (23 of 33 vp
positive, 69.7%) than in the low expression group (13 of 32 vp
positive, 40.6%), and poorly-differentiated HCC showed higher
Ube2c expression levels than well-differentiated HCC (p < 0.05).
No other significant differences were observed with respect to age,
gender, tumor size, capsular formation (fc), invasion to hepatic
vein (vv), invasion to bile duct (b) and number of tumors.
Analysis of disease-free survival curves showed that patients in
the high expression group had a significantly poorer prognosis
than those in the low expression group (p < 0.01) (Fig. 2). How-
ever, overall survival rates between the 2 groups were not statisti-
cally different (data not shown).
Univariate analysis identified Ube2c expression (low or high
expression), tumor size (? or >3 cm) and number of tumors (soli-
tary or multiple) as adverse prognostic factors for disease-free sur-
vival after hepatic resection. Variables with a p value of less than
0.15 by univariate analysis were selected for multivariate analysis
using Cox’s proportional hazards model. Ube2c expression (rela-
tive risk (RR): 1.51, confidence interval (CI): 1.06–2.22, p 5
0.02) was found to be a significant factor affecting disease-free
survival rate following hepatic resection (Table II).
Ube2c protein expression in clinical tissue specimens. Ube2c
protein expression in tumor and normal tissues from representative
FIGURE 1 – (a) Expression of Ube2c mRNA as assessed by RT-PCR in representative HCC cases. (T, cancer tissue; N, noncancerous tissue;
n, negative control; p, positive control; m, marker) (b) Ube2c mRNA expression in cancer and noncancerous tissues from HCC patients as
assessed by real-time quantitative PCR (n 5 65). Horizontal lines indicate mean value of each group. (T, cancer tissue; N, noncancerous tissue)
(c) Expression of Ube2c protein by western blot in representative HCC patient tissues. Ube2c protein was detected as a band of ?20 kDa. (T,
cancer tissue; N, noncancerous tissue; p, positive control; m, marker) (d) Immunohistochemistry with Ube2c antibody on HCC patient samples.
The majority of staining occurred in cancer cells. (a): cancer tissue, original magnification 3200, Ube2c stain, (b): noncancerous tissue, original
magnification 3200, Ube2c stain.
OVEREXPRESSED GENES IN HCC; A SPECIAL REFERENCE TO Ube2c
HCC patients was examined by western blot. Strong Ube2c pro-
tein expression was observed in the cancer tissues (Fig. 1c).
Immunohistochemical staining. Ube2c staining was stronger in
cancer tissues than in corresponding noncancerous liver tissues.
Ube2c expression was localized to cell nuclei (Fig. 1d). Expres-
sion of Ube2c in poorly differentiated HCC was detected in nuclei
Effect of Ube2c gene silencing on an HCC cell line. As
described earlier, Hep-3B cells showed high Ube2c expression
levels. Suppression of Ube2c mRNA was confirmed by real-time
quantitative PCR (50% suppression) (Fig. 3a). Protein expression
was suppressed by Ube2c-specific siRNA in western blots
(Fig. 3b). As shown in Figure 3c, suppression of Ube2c inhibited
the proliferation rate of Hep3B HCC cells (96 hr Ube2c siRNA:
1.92 6 0.40, negative siRNA: 2.97 6 0.36, control: 3.29 6 0.29)
(p < 0.01).
This study identified differentially expressed genes between
HCC and normal liver tissues (Supplementary 1). Diubiquitin
(FAT10) was the most upregulated gene and belongs to the ubiqui-
tin-like modifier (UBL) family. It has been reported that upregula-
tion of FAT10 expression in tumors was observed in 90% of HCC
patients.19Another highly upregulated gene was glypican-3
(GPC3), a member of the glypican family of glycosyl-phosphati-
dylinositol-anchored cell-surface heparin sulfate proteoglycans.20–
22GPC3 is also reported to be expressed in most HCC cells, but
not in normal hepatocytes and benign liver lesions,23,24and serum
GPC3 protein levels are elevated in a large proportion of HCC
patients.25Midkine (MDK) is a member of the heparin-binding
growth factor family and increased MDK expression has been
reported in various human cancers including HCC, and signifi-
cantly elevated serum MDK levels are observed in cancer patients.
It is thought that MDK acts as an antiapoptotic factor in HepG2
cells through the down-regulation of caspase-3 activity. Other
genes reported to be associated with HCC (SPINK1, ROBO1,
PLA2G2A, PEG10 and so on) were also included in the list of
FIGURE 2 – Kaplan-Meier disease-free survival curves for HCC
patients according to the level of Ube2c mRNA expression. The recur-
rence rate for patients in the high expression group was significantly
higher than that for patients in the low expression group (p < 0.01).
High expression group (n 5 33): Ube2c/GAPDH ? median value,
Low expression group: Ube2c/GAPDH < median value (n 5 32).
TABLE I – Ube2c GENE EXPRESSION AND CLINICOPATHOLOGICAL
FEATURES FOR 65 HCC PATIENTS
Clinicopathologic variable High expression
group (n 5 33)
group (n 5 32)
Capsular formation (fc)
Invasion to capsular formation (fc-inf)
Invasion to portal vein (vv)
Invasion to hepatic vein (vp)
Invasion to bile duct (b)
Number of tumors
65.3 6 11.2 66.7 6 9.10.59
4.2 6 3.8 3.2 6 1.90.21
High expression group (Ube2c/GAPDH ? median value), Low
expression group (Ube2c/GAPDH < median value). Well, well differ-
entiated; poor, poorly differentiated; moderate, moderately differenti-
ated; HBV, hepatitis B virus; HCV, hepatitis C virus; LC, liver cirrho-
sis; fc-inf, invasion to capsule or outside of capsule. Cases with no
capsule formation were included in fc-inf (2).
TABLE II – RESULTS OF UNIVARIATE AND MULTIVARIATE ANALYSES OF
CLINICOPATHOLOGICAL FACTORS AFFECTING DISEASE FREE-SURVIVAL
RATE FOLLOWING SURGERY
p value Relative
Number of tumors
0.11 1.16 0.45
n, number of patient; CI, confidence interval; fc, capsular formation;
fc-inf, tumor invasion to capsular formation; vp, invasion to portal vein;
vv, invasion to hepatic vein; b, invasion to bile duct; Ube2c, Ube2c
expression; high, high expression group (Ube2c/GAPDH ? median
value); low, low expression group (Ube2c/GAPDH < median value).
IETA ET AL.
Of the overexpressed genes we identified, we further studied the
Ube2c gene that was expressed 3 times higher in HCC cells than
in normal liver cells. Ube2c is highly expressed in various human
cancers, including ovarian carcinoma, metastatic prostate carci-
noma and thyroid anaplastic carcinoma.9–13Okamoto et al.
showed that Ube2c expression was low in many normal tissues
but was prominent in the majority of cancer cell lines, and that
high Ube2c expression levels were observed in primary tumors
derived from lung, stomach, uterus and bladder when compared
with corresponding normal tissues.11Ube2c has also been reported
to be overexpressed in primary colorectal cancers and in subse-
quent liver metastases and was identified as an overexpressed and
myc-interacting gene in human glioma.29However, none of the
previous studies investigated the clinicopathological significance
of increased Ube2c expression in HCC.30In the present study, we
compared various clinicopathological factors with respect to
Ube2c expression status in HCC. Our findings indicated that
Ube2c expression was higher in HCC than in noncancerous liver
tissues, and that Ube2c overexpression was significantly associ-
ated with fc-inf, vp, tumor grade (p < 0.05) and poor prognosis in
terms of disease free survival (p < 0.01) in HCC patients. In addi-
tion, multivariate analysis showed that Ube2c expression was an
independent prognostic factor associated with the disease-free sur-
vival rate. These findings suggested that enhanced expression of
Ube2c may play an important role in various pathological proc-
esses of HCC. Our finding of high expression levels detected in
poorly-differentiated HCC agreed with reports that showed that
Ube2c expression was associated with poor tumor differentiation
in ovarian, breast, lung, bladder and brain cancers.11,12
The function of the Ube2c gene product is closely linked to cell
cycle progression and the destruction of mitotic cyclins. Rape and
Kirschner showed that the decision between cyclinA degradation
and APC inactivation is determined by Ube2c availability.7,8Our
study demonstrated that siRNA-mediated suppression of Ube2c
expression inhibited the growth rate of an HCC cell line, which
was consistent with reports that NIH3T3 cells stably transfected
with Ube2c exhibited a more malignant phenotype than the paren-
tal NIH3T3 cells,11such that Ube2c gene silencing by siRNA
inhibited cell proliferation without inducing cell death, with cell
cycle analysis by FACS following Ube2c siRNA treatment show-
ing arrest at the G2/M phase.12,31,32Furthermore, when combined
with agonists for the DR5/TNF-related apoptosis inducing ligand
(TRAIL) receptor, inhibition of Ube2c by siRNA enhanced tumor
cell killing.12Therefore, in HCC patients, high Ube2c expression
may lead to increased malignant potential of the tumor, such that
the Ube2c gene may have some utility as a therapeutic target.
The Ube2c gene was found to be overexpressed in gastro-
esophageal cancer, with chromosomal amplification at the Ube2c
locus, 20q13.1, shown.12,3320q amplification is common among
various carcinomas,34–37including HCC,38so it is likely that this
amplification would induce Ube2c overexpression, thereby
increasing the malignant potential of HCC cells.
In conclusion, our study identified upregulated genes in HCC
cells compared to normal liver cells, and also showed that one of
the upregulated genes, Ube2c, may play an important role in
HCC, and may prove useful as a novel prognostic marker for
patients with HCC.
We thank Ms. T. Shimooka, Ms. K. Ogata, Ms. M. Oda,
Ms. M. Kasagi and Ms. Y. Nakagawa for their technical assistance.
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