AKIRIN2 has high expression in GA
Based on the TCGA database, we explored the expression of AKIRIN2 in 227 GA samples and 32 normal samples. The findings reflected that AKIRIN2 is highly expressed in tumor samples (Figure 1A). To confirm this result, we used GSE19826 (12 tumor samples and 15 normal samples) from GEO database to verify (Figure1B). The analysis results of the two databases showed that AKIRIN2 is highly expressed in tumors. To further determine the results, we randomly selected 10 gastric cancer samples and corresponding normal adjacent from the sample library. We found that AKIRIN2 was up-regulated in gastric cancer (Figure 1C,D).
Prognostic value of AKIRIN2 in GA
Next, we explored the correlation between AKIRIN2 and clinical features. According to the expression of AKIRIN2, patients were divided into high- and low-expression groups. We collated the clinical data of the two groups, including gender, age, tumor grade, and tumor stage, to evaluate the correlation between clinical parameters and AKIRIN2 (Table1). However, we did not find any significant difference in the clinical features between the two groups. The heatmap showed the correlation between clinical characteristics with AKIRIN2 expression and the clustering of differentially expressed genes in the high- and low-expression AKIRIN2 groups (Figure 2A). Next, K–M analysis assessed whether the expression of AKIRIN2 has an effect in GA over survival (Figure 2B). Patients in the low-expression group had a longer survival time than those in the high-expression group (P=0.031). Then, univariate and multivariate Cox regression analyses were performed to research the correlation between overall survival (OS) and clinical characteristics. The univariate Cox regression forest plot demonstrated that tumor stage III, IV (P=0.013), and the level of AKIRIN2 (P=0.031) were identified as independent risk factors to affect the OS of GA patients (Figure 2C). In addition, multivariate Cox proportional hazards regression analysis determined the clinical features that contributed to the OS. The findings also showed that stage III, IV and AKIRIN2 were significantly connected with OS, as shown in Figure 2D. These results suggested that AKIRIN2 expression is an independent clinical factor affecting the OS and prognosis of GA patients.
Table 1
Correlation between the expression level of AKIRIN2 and clinical characteristics
|
|
Expression of AKIRIN2
|
|
Characteristics
|
Number of cases (%)
|
Low (number of cases)
|
High (number of cases)
|
P-value
|
Gender
|
|
|
|
|
female
|
98 (35.4)
|
47
|
51
|
0.673
|
male
|
179 (64.6)
|
92
|
87
|
|
Age
|
|
|
|
|
>=70
|
108 (38.9)
|
49
|
59
|
0.201
|
<70
|
169 (61.1)
|
90
|
79
|
|
Tumor Grade
|
|
|
|
|
G1+G2
|
109 (39.4)
|
59
|
50
|
0.350
|
G3
|
168 (60.6)
|
80
|
88
|
|
Tumor Stage
|
|
|
|
|
Stage1+2
|
122 (44.1)
|
64
|
58
|
0.581
|
Stage3+4
|
155 (55.9)
|
75
|
80
|
|
Enrichment analysis of AKIRIN2-related signaling pathways
In order to explore the functional phenotype between high- and low-expression groups, the GO function and KEGG and Hallmark pathway were analyzed in the upregulated DEGs. The GO annotation results revealed that the biological processes were primarily associated with organelle fission, nuclear division, regulation of cell cycle phase transition, regulation of mitotic cell cycle phase transition, chromosome segregation, and mitotic nuclear division (Figure 3A). Moreover, the KEGG pathway analysis identified the genes involved in cell cycle, T-cell leukemia virus 1 infection, Epstein-Barr virus infection, microRNAs in cancer, Staphylococcus aureus infection, DNA replication, Leishmaniasis, primary immunodeficiency, viral myocarditis, and p53 signaling pathway (Figure 3B). The bubble chart of Hallmark gene sets show the genes enriched in E2F targets, G2M checkpoint, gamma response, allograft rejection, myc target v1, mitotic spindle, interferon-alpha response, complement, and IL6-JAK-STAT3 signaling (Figure 3C). The findings validated that DEGs are mostly enriched in cell cycle progression, proliferation, and differentiation-related pathways, thereby indicating that AKIIN2 plays a major role in regulating cell proliferation and cell survival, which is consistent with previous studies[28].
AKIRIN2 expression is correlated with immune infiltration and immune cells
To investigate the effect of AKIRIN2 expression on different immune cell types in the GA microenvironment, we downloaded the distribution of 24 immune cells of GA samples from ImmunecellAI and analyzed the linear correlation between the expression of AKIRIN2 and the expression of infiltration score by Pearson’s correlation analysis (Figure 4A). The AKIRIN2 expression was significantly correlated with immune scores (R=0.14, P<0.024). Figure 4B shows the distribution of 24 types of immune cells in 277 samples. Next, we compared the level of immune cells in the high-and low-expression AKIRIN2 groups. A total of 8 different immune cells were related to the expression of AKIRIN2 (P<0.05), as shown in Figure 4C. Tc, Tex, Th1, NK, Tgd and CD8+ T were positively correlated with AKIRIN2 expression, while MALT and Th17 were negatively correlated.
Immune cells closely related to AKIRIN2 expression
Moreover, we studied the correlation between AKIRIN2 expression and the immune cell abundance based on Pearson’s correlation coefficient analysis (Table 2). We found that the high expression of AKIRIN2 was positively correlated with the expression of iTreg, Tc, CD8+ T, and Tex but negatively correlated with the expression of Th17 and MALT (P<0.001). Next, a combination of CIBERSORT, TIMER, and ImmuneCellAI analyzed the correlation between various immune cell subtypes and AKIRIN2 expression to verify that the immune cells in GA are specifically affected by AKIRIN2 expression. Figure5 shows the expression of immune cells in three databases. CD8+ T cell count is positively correlated with AKIRIN2 in both ImmuCellAI and CIBERSORT databases. CD4+ memory T cells is also activated, which is consistent with the results from TIMER and CIBERSORT databases.
Table 2
Correlation between AKIRIN2 and the abundance of immune cells
|
Expression of AKIRIN2
|
Cell types
|
Pearson's correlation
|
P-value
|
Th17
|
-0.323
|
<0.001
|
MAIT
|
-0.289
|
<0.001
|
NKT
|
-0.169
|
0.005
|
Monocyte
|
-0.158
|
0.009
|
Tgd
|
0.126
|
0.036
|
NK
|
0.182
|
0.003
|
iTreg
|
0.196
|
<0.001
|
Tc
|
0.204
|
<0.001
|
CD8_T
|
0.212
|
<0.001
|
Th1
|
0.295
|
<0.001
|
Tex
|
0.316
|
<0.001
|
Predicting response to chemotherapy and immunotherapy
Herein, we also assessed the role of AKIRIN2 in chemotherapy and immunotherapy for GC. Chemotherapy is a common treatment for patients with advanced GC. The IC50 for each sample in the TCGA-STAD dataset was estimated based on the predictive model of chemotherapeutics. The ridge regression method was used to train the prediction model on the GDSC cell line data set, and the 10-fold cross-validation method was used to evaluate the prediction accuracy. Cisplatin, paclitaxel, and 5-fluorouracil showed significant differences in the estimated IC50 against the high-expression group. The results showed that GA with high expression of AKIRIN2 is sensitive to commonly used chemotherapy (Figure 6A).
The submap algorithm was used to predict the possibility of responding to immunotherapy. Subclass mapping was used to compare the expression profiles of the two groups with the dataset of an open melanoma treatment cohort of 47 melanoma patients receiving programmed cell death protein-1 (PD-1) or cytotoxic T lymphocyte-associated protein-4 (CTLA-4) immunosuppression. Finally, a significant correlation (P<0.001) was established between the high expression of AKIRIN2 and PD-1 responders (Figure 6B), suggesting that patients in the high-expression AKIRIN2 group adequately responded to anti-PD-1 therapy.