3.1 Expression and prognosis analyses on APOH
We firstly explored the potential value of APOH in human cancers of the urinary system. Expression analysis showed that APOH was just down-regulated in 3 tumor types of kidney cancer (Fig.1A). The abnormal expression of APOH was not observed in BLCA and PRAD. We also assessed its prognostic impact, and the result indicated that APOH only influenced the survival time of KIRC patients among 5 cancer types (Fig.1B). These findings initially highlighted the importance of APOH in KIRC.
We further investigated the role of APOH in KIRC. The immunohistochemical images showed that the staining of APOH protein in normal cells was high, while it was not detected in tumor cells (Fig.2A). In addition, it was found that the APOH protein was mainly located at cytoplasmic/membranous. Qualitative analysis on APOH mRNA expression showed that it was downregulated in KIRC tumor tissues compared with normal tissues (Fig.2B). The paired-sample analysis also confirmed the downregulation of APOH mRNA expression in KIRC tissues (Fig.2C).
Based on the clinical data of KIRC patients, we assessed the relationship between APOH mRNA expression and clinical characteristics of patients (Fig.3). The results showed that age, hemoglobin, platelet qualitative, and WBC did not influence the mRNA expression of APOH. However, higher expression of APOH mRNA was observed in male patients and these patients with grade 4, elevated serum calcium, person neoplasm status with tumor, stage IV, T3 stage, N1 stage, and M1 stage. It followed that APOH mRNA expression was related to several clinical phenotypes of KIRC patients.
Then, we evaluated the effect of APOH mRNA expression on the OS, DFI, PFI, and DSS of KIRC patients by Kaplan-Meier analysis and log-rank test (Fig.4). Survival analysis indicated that the DFI showed no difference between APOH high and low expression groups. But, APOH high expression significantly shortened the OS, PFI, and DSS time of KIRC patients compared with low expression.
Due to the vital role of APOH on the OS, PFI and DSS of KIRC patients, we then explored the prediction performance of APOH on these clinical outcomes in KIRC. The ROC analysis in Fig.5 showed that APOH presented a better prognostic performance on OS, PFI, and DSS in KIRC, and the AUC was 0.598, 0.651, and 0.631, respectively.
Table.1 Cox regression analysis in KIRC based on TCGA clinical data
|
|
Univariate
|
Multivariate
|
|
P
|
HR (95% CI)
|
P
|
HR (95% CI)
|
OS (overall survival)
|
|
|
|
|
APOH expression
|
0.020
|
1.200 (1.029-1.400)
|
0.068
|
0.778 (0.595-1.018)
|
age
|
<0.001
|
1.031 (1.017-1.044)
|
0.020
|
1.028 (1.004-1.052)
|
hemoglobin
|
<0.001
|
0.484 (0.342-0.683)
|
0.333
|
0.778 (0.595-1.018)
|
grade
|
<0.001
|
2.722 (2.016-3.677)
|
0.712
|
1.085 (0.703-1.676)
|
stage
|
<0.001
|
1.906 (1.668-2.179)
|
<0.001
|
1.624 (1.239-2.129)
|
person neoplasm status
|
<0.001
|
4.916 (3.509-6.888)
|
0.001
|
2.594 (1.442-4.665)
|
platelet qualitative
|
0.004
|
1.823 (1.215-2.736)
|
0.751
|
0.921 (0.552-1.535)
|
serum calcium
|
0.003
|
1.584 (1.164-2.156)
|
0.591
|
1.125 (0.732-1.728)
|
white cell count
|
0.038
|
0.706 (0.508-0.981)
|
0.593
|
0.879 (0.547-1.411)
|
gender
|
0.774
|
1.047 (0.764-1.434)
|
0.641
|
0.893 (0.555-1.437)
|
PFI (progression-free interval)
|
APOH expression
|
<0.001
|
1.210 (1.111-1.318)
|
0.040
|
0.784 (0.621-0.989)
|
age
|
0.481
|
1.005 (0.992-1.018)
|
0.482
|
1.008 (0.985-1.032)
|
hemoglobin
|
0.011
|
0.647 (0.463-0.904)
|
0.002
|
2.523 (1.403-4.537)
|
grade
|
<0.001
|
3.660 (2.660-5.037)
|
0.079
|
1.550 (0.950-2.527)
|
stage
|
<0.001
|
2.716 (2.324-3.174)
|
<0.001
|
2.043 (1.530-2.727)
|
person neoplasm status
|
<0.001
|
46.638 (25.745-84.487)
|
<0.001
|
44.957 (15.561-129.883)
|
platelet qualitative
|
0.001
|
1.955 (1.304-2.932)
|
0.688
|
1.130 (0.622-2.055)
|
serum calcium
|
0.008
|
1.547 (1.120-2.138)
|
0.024
|
0.597 (0.381-0.935)
|
white cell count
|
0.008
|
0.635 (0.454-0.888)
|
0.271
|
1.332 (0.799-2.220)
|
gender
|
0.020
|
0.662 (0.468-0.937)
|
0.055
|
0.594 (0.350-1.010)
|
DSS (disease-specific survival)
|
APOH expression
|
0.005
|
1.180 (1.051-1.326)
|
0.082
|
0.784 (0.596-1.031)
|
age
|
0.210
|
1.010 (0.994-1.026)
|
0.208
|
0.684 (0.378-1.235)
|
hemoglobin
|
0.001
|
0.483 (0.315-0.741)
|
0.702
|
0.882 (0.464-1.676)
|
grade
|
<0.001
|
3.878 (2.662-5.650)
|
0.777
|
1.071 (0.658-1.752)
|
stage
|
<0.001
|
3.045 (2.473-3.750)
|
0.001
|
1.836 (1.297-2.598)
|
person neoplasm status
|
<0.001
|
275.338 (36.005-2105.572)
|
0.837
|
1.987e+5 (0-7.565e+55)
|
platelet qualitative
|
<0.001
|
2.802 (1.767-4.444)
|
0.130
|
1.643 (0.864-3.121)
|
serum calcium
|
0.003
|
1.763 (1.210-2.570)
|
0.274
|
0.756 (0.459-1.247)
|
white cell count
|
0.036
|
0.651 (0.436-0.973)
|
0.774
|
0.920 (0.519-1.629)
|
gender
|
0.251
|
0.785 (0.517-1.186)
|
0.208
|
0.684 (0.378-1.235)
|
Subsequently, we performed the Cox regression analysis to explore the prognosis-related factors in KIRC in terms of different clinical outcomes. The univariate analysis showed that APOH was one of the important influencing factors of OS, DFI, and DSS in KIRC (Table.1). But the independent prognostic value of APOH was just determined regarding the PFI of KIRC patients.
According to the multivariate Cox regression analysis, APOH only independently predicted the PFI in KIRC patients. Hence, we further enrolled the independent prognostic factors of PFI into the nomogram construction to reveal their contribution. The nomogram analysis (Fig.6A) showed that the person neoplasm status made the largest contribution to the survival probability of patients, with a single contribution of 100 points. We also constructed the calibration curve of nomogram predicted survival (Fig.6B), suggesting the better prediction performance of APOH on the survival probability of KIRC patients.
3.2 Methylation and prognosis analyses on APOH
Moreover, the Pearson correlation analysis showed a strong negative relationship between APOH mRNA expression and methylation level (Fig.7A), suggesting the importance of APOH methylation on its mRNA expression. According to the analysis, we found that the methylation level of APOH in tumor tissue was significantly lower than that in normal tissues (Fig.7B). Further investigations showed that the methylation difference of APOH between normal and tumor tissues was related to the methylation probe. Among 6 probes, the methylation level of cg19058765 was higher in the tumor than in the normal group (Fig.7C).
Table.2 The Cox regression model analysis on methylation level of APOH
|
Probe ID
|
Coef
|
HR
|
Lower (95%)
|
Upper (95%)
|
P-value
|
cg04006839
|
0.078
|
1.081
|
2.44E-01
|
4.804
|
0.917
|
cg09732045
|
0.568
|
1.765
|
2.64E-02
|
117.908
|
0.790
|
cg14334014
|
-8.78503
|
0.000153
|
1.36E-08
|
1.724
|
0.064
|
cg16481618
|
0.48827
|
1.62949
|
2.50E-01
|
10.639
|
0.610
|
cg17095279
|
-3.1386
|
0.043343
|
5.18E-03
|
0.362
|
0.003
|
cg19058765
|
4.23954
|
69.375664
|
1.01E+00
|
4788.591
|
0.049
|
Then the Cox regression model analysis was performed to predict prognosis-related methylation probes of APOH. As shown in Table.2, the cg17095279 and cg19058765 showed the correlation with the patient's prognosis among 6 probes. We also performed the Kaplan-Meier analysis on cg17095279 and cg19058765 to explore their prognostic impacts. The survival analysis indicated that the methylation level of these 2 probes did not affect the patient's OS, DFI, and PFI (Fig.8).
3.3 Correlation analysis between APOH and immune infiltrates in KIRC
We also explored the relationship between APOH and immune infiltrates in KIRC. As shown in Fig.9, APOH expression was strongly related to several immune cells such as CD4_cell, CD_8 cell, and monocyte. In addition, it was observed that the methylation of APOH was also related to immune infiltrates such as B_cell, CD_4 cell, neutrophils, and CD8_cell. However, no correlation between APOH mutation and immune infiltrates was observed in KIRC.
Table.3 Cox regression analysis on immune infiltrates and APOH in KIRC
|
|
Univariate
|
Multivariate
|
|
P
|
HR (95% CI)
|
P
|
HR (95% CI)
|
B cell
|
0.961
|
1.408 (0.155-7.091)
|
0.553
|
0.368 (0.014-10.000)
|
CD4_T cell
|
0.715
|
1.391 (0.237-8.177)
|
0.749
|
0.644 (0.043-9.569)
|
Macrophage
|
0.291
|
0.412 (0.080-2.136)
|
0.015
|
0.053 (0.005-0.560)
|
CD8_T cell
|
0.259
|
0.581 (0.227-1.491)
|
0.042
|
0.196 (0.041-0.940)
|
Neutrophil
|
0.575
|
1.902 (0.201-17.96)
|
0.144
|
22.268 (0.347, 1427.911)
|
Dendritic
|
0.788
|
1.095 (0.567-2.113)
|
0.191
|
3.333 (0.548-20.279)
|
APOH
|
0.050
|
1.097 (1.000-1.203)
|
0.022
|
1.121 (1.017-1.237)
|
The Cox regression analysis was also performed to predict prognosis-related factors (Table.3). In the univariate Cox regression, we found no prognostic impacts of all immune infiltrates and APOH. However, when adding these variables into multivariate Cox analysis, the macrophage, CD8_T cell, and APOH showed the independent prognostic value. According to the results, the potential correlation between APOH and several immune infiltrates needed further assessment.
3.4 Pathway enrichment analysis
We used GeneMANIA to predict the related genes that may have the same function and interaction with APOH and predicted the potential functions of APOH. The function prediction (Fig.10) indicated that APOH was closely related to hemostasis, coagulation, complement activation, and negative regulation of blood coagulation, referring to the regulation of blood coagulation.
In order to reveal the potential function of APOH, we selected the top 100 co-expressed genes of APOH in cBioportal for pathway enrichment analysis. The KEGG analysis (Fig.11A) showed that these co-expressed genes were mainly enriched in Complement and coagulation cascades, and Staphylococcus aureus infection pathways. In addition, the Folate biosynthesis, Cholesterol metabolism, and Pathogenic Escherichia coli infection pathways were also predicted. GSEA analysis was then used to explore the potential correlation between APOH and significant pathways in KIRC, and the results presented that APOH showed a significant positive correlation with Complement and coagulation cascades, and Staphylococcus aureus infection pathways (Fig.11B). We speculated that APOH largely participated in Complement and coagulation cascades involved in KIRC.