The clinical significance of snail protein expression in gastric cancer: a meta-analysis
Chen et al. Human Genomics
The clinical significance of snail protein expression in gastric cancer: a meta- analysis
Xiaoya Chen 0
Jinjun Li 0
Ling Hu 3
William Yang 2
Lili Lu 0
Hongyan Jin 7
Zexiong Wei 7
Jack Y. Yang 6
Hamid R. Arabnia 4
Jun S. Liu 5
Mary Qu Yang 6
Youping Deng 0 1
0 Medical College, Wuhan University of Science and Technology , Wuhan 430065 , China
1 Department of Internal Medicine and Rush University Cancer Center, Rush University Medical Center , Chicago, IL 60612 , USA
2 Texas Advanced Computing Center, University of Texas at Austin , 10100 Burnet Road, Austin, TX 78758 , USA
3 Department of Anesthesiology, Tianyou Hospital, Wuhan University of Science and Technology , Wuhan 430064 , China
4 Department of Computer Science, University of Georgia , Athens, GA 30602 , USA
5 Department of Statistics and Harvard School of Public Health, Harvard University , One Oxford St., Cambridge 02138 Massachusetts , USA
6 MidSouth Bioinformatics Center, Department of Information Science, George Washington Donaghey College of Engineering and Information Technology and Joint Bioinformatics Graduate Program, University of Arkansas at Little Rock and University of Arkansas for Medical Sciences , 2801 S. University Avenue, Little Rock, AR 72204 , USA
7 Puren Hospital, Wuhan University of Science and Technology , Wuhan 430081 , China
Background: Snail is a typical transcription factor that could induce epithelial-mesenchymal transition (EMT) and cancer progression. There are some related reports about the clinical significance of snail protein expression in gastric cancer. However, the published results were not completely consistent. This study was aimed to investigate snail expression and clinical significance in gastric cancer. Results: A systematic review of PubMed, CNKI, Weipu, and Wanfang database before March 2015 was conducted. We established an inclusion criterion according to subjects, method of detection, and results evaluation of snail protein. Meta-analysis was conducted using RevMan4.2 software. And merged odds ratio (OR) and 95 % CI (95 % confidence interval) were calculated. Also, forest plots and funnel plot were used to assess the potential of publication bias. A total of 10 studies were recruited. The meta-analysis was conducted to evaluate the positive rate of snail protein expression. OR and 95 % CI for different groups were listed below: (1) gastric cancer and para-carcinoma tissue [OR = 6.15, 95 % CI (4.70, 8.05)]; (2) gastric cancer and normal gastric tissue [OR = 17.00, 95 % CI (10.08, 28.67)]; (3) non-lymph node metastasis and lymph node metastasis [OR = 0.40, 95 % CI (0.18, 0.93)]; (4) poor differentiated cancer, highly differentiated cancer, and moderate cancer [OR = 3.34, 95 % CI (2.22, 5.03)]; (5) clinical stage TI + TII and stage TIII + TIV [OR = 0.38, 95 % CI (0.23, 0.60)]; (6) superficial muscularis and deep muscularis [OR = 0.18, 95 % CI (0.11, 0.31)]. Conclusions: Our results indicated that the increase of snail protein expression may play an important role in the carcinogenesis, progression, and metastasis of gastric cancer. And this result might provide instruction for the diagnosis, therapy, and prognosis of gastric cancer.
Gastric cancer; Snail; Meta-analysis
Epithelial-mesenchymal transition (EMT), a developmental
process whereby epithelial cells reduce intercellular
adhesion and acquire myofibroblastic features, is critical
to tumor progression [
]. Meanwhile, the dissolution of
intercellular adhesions and the acquisition of a more
motile mesenchymal phenotype as part of
epithelialto-mesenchymal transition (EMT) are crucial capacities of
invading cancer cells [
]. Snail can induce EMT partly by
suppressing the expression of E-cadherin. Reduced
expression of E-cadherin may lead to the loss of cell-cell
adhesion and cancer progression [
]. In recent years, snail
was found to be highly expressed in several carcinomas,
including non-small cell lung carcinomas, ovarian
carcinomas, urothelial carcinomas, breast cancer, and
hepatocellular carcinoma [
]. Studies of immunohistochemical
analyses suggest that snail is highly expressed in gastric
cancer and significantly associated with tumor progression
and metastasis [
Study search protocol
A total of 10 studies were identified by primary search
strategies using the keywords “snail” combined with
“gastric cancer” and synonyms in PubMed, CNKI,
Weipu, and Wanfang database.
Inclusion criteria and exclusion criteria
Studies that were included in this meta-analysis met the
following criteria: (1) the official published literature or
master’s and doctoral dissertation in both Chinese and
English before March 2015; (2) the detection method
used immunohistochemical and the results experienced
quantitative analysis; (3) when duplicate articles were
published, we included the newest or the most
informative single study; (5) the snail positive rate was given or
could be calculated based on the information from tables
Exclusion criteria included (1) repetitive studies; (2)
research on animal and cellular level; (3) studies without
reviews, letters, abstracts and editorials; and (4) the studies
without control group.
Data extraction and quality assessment
Two reviewers screened the titles and abstracts
according to the inclusion and exclusion criteria listed above
independently. Then, they cross-checked the articles and
removed disagreements. Information extracted from the
eligible articles included first author, publication year,
detection method, the number of cases and controls, the
clinical pathology states of cases and controls, and the
location of snail protein expression. The quality of these
studies is assessed by the following: (1) whether the gold
standard method is set up; (2) whether the gold standard
test stayed is independent of the evaluation test; (3)
whether the blind method is used; (4) whether
quantitative data is given or is able to be calculated; (5) whether
the definition and diagnosis of the case are correct,
independent, and standard; (6) whether the diagnostic steps
are detailed; (7) whether the case has a good
representation; (8) whether cases and controls are selected and
analyzed based on the most important factor. Based on
the above standards, we classified the qualities of the
research into five grades: (A) meets all 8 quality standards;
(B) meets 7 standards; (C) meets 6 standards; (D) meets
5 standards; (E) meets 4 standards.
Meta-analysis was conducted with RevMan4.2 software.
Odds ratio (OR) with 95 % confidence interval was
calculated. Heterogeneity between studies was examined
using the I2 statistic [
]. When I2 value was greater
than 50 %, we considered that heterogeneity was
significant. Fixed-effect Mantel-Haenszel model was chosen as
the main analysis method when the heterogeneities were
not confirmed statistically significant. Otherwise,
randomeffect model was adopted. Funnel plots were used to
check for the potential of publication bias. All the P values
were two-sided, and statistically significant difference was
defined as P < 0.05.
Literature search and study characteristics
After reviewing the abstracts and titles of 183 studies,
173 of them were excluded. In detail, 49 studies were
excluded due to repetition; 32 studies were due to
non-human subjects; 7 studies were due to
non-fulltext; 14 studies were due to non-IHC study; 69
studies were due to missing control group; 2 studies were
due to missing the snail positive rate. Eventually, 10
articles were collected [
] (Fig. 1). Detailed
characteristics of these 10 eligible studies are summarized
in Table 1. A total of 756 gastric cancer tissue
samples, 346 para-carcinoma tissue samples, and 171
normal tissue samples were used in these 10 studies.
Eight of them reported the relationship between the
snail expression and clinical pathology, enrolled the
degree of differentiation, the lymph node metastasis,
TNM stage, and invasion depth.
Eight of the ten studies compared the expression of
snail protein in gastric cancer tissues and the
adjacent tissues, including 684 gastric cancer
samples and 475 para-carcinoma samples. The I2 value
was 0 % and less than 50 %; thus, we chose
fixedeffect Mantel-Haenszel model for further analysis.
The overall effect was Z = 13.20. The odds ratio
(OR) was 6.15 with 95 % CI = (4.70, 8.05), and P <
0.001 (Fig. 2).
Five of the ten studies compared the positive
expression of snail protein in gastric cancer tissues
with that in normal tissues, including 455 gastric
cancer tissue samples and 171 normal samples. The I2
value was 49.7 % and less than 50 %; thus, we chose
fixed-effect Mantel-Haenszel model for further analysis.
The overall effect was Z = 10.63. The odds ratio was
17 with 95 % CI = (10.08, 28.67), and P < 0.001
The relationship between the expression of snail protein and the characteristics of clinical pathology
Eight studies analyzed the relationship between snail
expression and lymph node metastasis. The results
indicated that the I2 value was 74.4 % and greater than
50 %; thus, we chose random-effect model for further
analysis. The overall effect was Z = 2.14, OR = 0.40, 95 %
CI = (0.18, 0.93), and P < 0.001 (Fig. 4). Seven studies
analyzed the relationship between snail expression and
the differentiation. The result indicated that the I2 value
was 0 % and less than 50 %; thus, we chose fixed-effect
Mantel-Haenszel model for further analysis. The overall
effect was Z = 5.80, OR = 3.34, 95 % CI = (2.22, 5.03), and
P < 0.001 (Fig. 5). Five studies analyzed the relationship
between snail expression and the TNM stage. The result
showed that the I2 value was 0 % and less than 50 %;
thus, we chose fixed-effect Mantel-Haenszel model for
further analysis. The overall effect was Z = 4.02, OR =
0.38, 95 % CI = (0.23, 0.60), and P < 0.001 (Fig. 6). Seven
studies analyzed the relationship between snail
expression and invasion depth. The result showed that I2 value
was 0 % and less than 50 %; thus, we chose fixed-effect
Mantel-Haenszel model for further analysis. The overall
effect was Z = 6.28, OR = 0.18, 95 % CI = (0.11, 0.31), and
P < 0.001 (Fig. 7).
Publication bias analysis
Funnel plot analysis for publication bias of these analytical
studies (as shown in Figs. 8, 9, 10, 11, 12, and 13)
indicated a low likelihood of publication bias.
Discussion and conclusions
The emerging roles of some key, EMT-related proteins
in cancer progression and their close relationship with
clinical pathology parameters make them attractive for
developing diagnostic biomarkers and therapies [
The transcriptional repression of E-cadherin is mediated
mainly by zinc finger transcription factors related to the
snail family (SNAIL1), zinc finger E-box binding
homeobox-2 (ZEB2), and basic helix-loop-helix family
]. Network analysis (Fig. 14) revealed
that snail expression was significantly correlated with
the expression of ZEB2, TWIST (Twist1 and Twist2),
and N-cadherin (CDH2). These gene expressions may be
regulated by snail at transcriptional level, and they also
interact with each other. N-cadherin, encoded by the
CDH2 gene, mediates cell-cell adhesion and renders
tumor cell migration and invasion . N-cadherin was
reported to be a prognostic marker [
], and the
upregulation correlated with advanced TNM stage and
poor survival [
]. In addition, TWIST can modulate
Ncadherin expression through directly interacting with an
E-box, a regulatory element within intron 1 of CDH2
], and expression of TWIST appears to be
indispensable for the entry of tumor cells into the bloodstream, a
significant early step towards metastasis [
]. ZEB2 is
also known as SIP1, which interacts through its
COOHterminal region with E-box element of E-cadherin gene
promoter and mediates its transcriptional repression by
recruiting corepressor complexes [
transcription factors form signaling networks that could
initiate and sustain the mesenchymal phenotypes of tumor
cells; therefore, the expression of these proteins could
define EMT occurrence in a tumor setting. For example,
a study in primary human gastric cancers revealed
elevated snail and twist expressions in diffuse-type gastric
cancer, whereas ZEB2/SIP1 was primarily expressed in
the intestinal type  (Fig. 14).
This meta-analysis was aimed to examine the expression
of transcription factor snail in different tissue samples and
the relationship between increased snail expression and
clinicopathological features of gastric cancer. This study
combined 756 gastric cancer tissue samples, 346
paracarcinoma samples, and 171 normal tissue samples from
10 individual studies. The results indicated that snail
expression is higher in gastric cancer tissues than that in
para-carcinoma tissues and normal tissues, respectively
(OR = 6.15, 95 % CI = 4.70, 8.05; OR = 17, 95 % CI = 10.08,
28.67). Furthermore, closed correlations were observed
between snail expression and clinicopathological
characteristics that included the lymph node metastasis, the
degree of differentiation, TNM stage, and invasion depth.
The positive expression rate of snail was higher in gastric
cancer tissues with lymphatic metastasis, OR = 0.40, 95 %
CI = (0.18, 0.93). The higher positive rate of snail is
connected with the lower differentiation degree, OR =
3.34, 95 % CI = (2.22, 5.03). The positive expression of
snail was higher at late clinical stage, OR = 0.38, 95 % CI
= (0.23, 0.60). Moreover, it appeared that the deeper the
infiltration was, the higher the expression of snail was, OR =
0.18, 95 % CI = (0.11, 0.31).
The result of funnel plot indicated an imminent
possibility of publication bias. Two potential biases
might be introduced. First, the languages in collected
papers were used in both Chinese and English, which
may lead to a language bias. Second, the majority of
collected studies did not use blind method, which
might result in a measurement bias. Hence, the
largescale samples and double blind statistical tests will be
investigated in the future study. Additionally, our
review only collected the publications that have full
text, since data that can be used for the methodology
assessment and meta-analysis were only available in
these publications with full text.
Our meta-analysis indicated that snail was highly
expressed in gastric cancer. In addition, the
overexpression of snail is significantly associated with tumor
progression and metastasis.
The authors declare that they have no competing interests.
YC, YD, and JL envisioned the project. YC and LL designed the work. YC and
LH constructed and validated the pathway models and performed the data
analysis, with assistance from WY. YC, ZW, and HJ screened the data. YC, MY,
WG, and HRA wrote the manuscript. YL polished the English. All authors read
and approved the final manuscript.
The research and publication of the research were supported by the Natural
Science Foundation Hubei Province of China (2011CDB236 and 2012FFB04903).
This article has been published as part of Human Genomics Volume 10
Supplement 2, 2016: From genes to systems genomics: human
genomics. The full contents of the supplement are available online at
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