PSTPIP1 has a higher expression in KIRC than in normal tissue. The Oncomine, GIAPIA, and UALCAN databases were used to evaluate the expression difference of PSTPIP1 at the mRNA level in different tissues. There was a significant increase in PSTPIP1 expression in many kinds of tumor tissue, especially in kidney renal clear cell carcinoma (KIRC) (Fig. 1A). Analysis of Oncomine databases showed that PSTPIP1 mRNA was expressed at higher levels in both gumz renal KIRC (Fig. 1B) and Lenburg renal (Fig. 1C) KIRC.
Figure 2. PSTPIP1 transcription in subgroups of KIRC patients. (A-B) Boxplot showing relative expression PSTPIP1 in KIRC and normal tissue samples (GIAPIA and UALCAN). (C–I) Association between PSTPIP1 expression and tumor grade of KIRC (C), individual cancer stage of KIRC (D), KIRC subtypes (E), nodal metastasis status (F), patient’s race (G), patient’s gender (H), patient’s age (I).
Then, the GIAPIA (Fig. 2A) and UALCAN databases were searched, and similar results were obtained. Analysis of the UALCAN database revealed that the median PSTPIP1 expression was 0.741 in normal samples (n=72) compared to 5.189 in primary tumor samples (n=533) (Fig. 2B). Based on tumor grade, the median PSTPIP1 expression was 0.741 (n=50) in normal samples compared to 6.32 (n=14) in grade 1, 4.523 (n=229) in grade 2, 5.412 (n=206) in grade 3, and 6.6 (n=76) in grade 4 (Fig. 2C). Based on individual cancer stages, it was 0.741 (n=72, normal) compared to 4.455 (n=267, stage 1), 5.8 (n=57, stage 2), 5.946 (n=123, stage 3), and 5.801 (n=84, stage 4) (Fig. 2D). These results suggested that PSTPIP1 has a significant increase of expression in tumor tissue regardless of KIRC subtypes (Fig. 2E), nodal metastasis status (Fig. 2F), tumor grade (Fig. 2C), individual cancer stages (Fig. 2D), patient’s race (Fig. 2G), patient’s gender (Fig. 2H), patient’s age (Fig. 2I).
The experimental evidence of differential PSTPIP1 protein expression between normal tissue and tumor tissue was collected by immunohistochemistry (IHC). The staining results showed obvious PSTPIP1 expression in tumor tissue (Fig. 3A-D) and low or no expression in normal tissue. In tumor tissue, high expression occurred in 65 (43.3%) samples, while low expression occurred in 85 (56.6%) samples. For normal tissue, only 5 (18.6%) samples had high expression, compared to 22 (81.4%) low expression samples. The chi-square test result was 5.893 (P<0.05), showing a significant difference.
Relationship between PSTPIP1’s expression and clinic pathological characteristics in KIRC. A chi-square test was used to analyze whether PSTPIP1 expression was correlated with clinical pathological characteristics. The results showed that the expression level was significantly related to tumor size (P=0.004), Edmonson grade (P=0.045), and TNM stage (P=0.013). Sex (P=0.769), age (P=0.629), metastasis (P=0.41), microvascular invasion (P=0.711) and PDL-1 (P=0.051) did not have statistically significant relevance to PSTPIP1 expression.
Table 1. Relationship between PSTPIP1 expression and clinical parameters of KIRC patients.
Clinical parameters
|
PSTPIP1 expression
|
|
|
Low(%)
|
High(%)
|
χ2
|
p-value
|
Gender
|
|
|
|
0.086
|
0.769
|
|
Male
|
62(72.9%)
|
46(70.8%)
|
|
|
|
Famale
|
23(27.1%)
|
19(29.2%)
|
|
|
Age (yrs.)
|
|
|
|
0.234
|
0.629
|
|
<55
|
32(37.6%)
|
27(41.5%)
|
|
|
|
>=55
|
53(62.4%)
|
38(58.5%)
|
|
|
Size
|
|
|
|
8.193
|
0.004
|
|
<5cm
|
54(63.5%)
|
26(40.0%)
|
|
|
|
>=5cm
|
31(36.5%)
|
39(60.0%)
|
|
|
metastasis
|
|
|
|
0.679
|
0.41
|
|
No
|
84((98.8%)
|
63(96.9%)
|
|
|
|
Yes
|
1(1.2%)
|
2(3.1%)
|
|
|
Microvascular invasion
|
|
|
|
0.138
|
0.711
|
|
No
|
77(90.6%)
|
60(92.3%)
|
|
|
|
Yes
|
8(9.4%)
|
5(7.7%)
|
|
|
Edmondson grade
|
|
|
|
4.004
|
0.045
|
|
Ⅰ~Ⅱ
|
64(75.3%)
|
39(60.0%)
|
|
|
|
Ⅲ~Ⅳ
|
21(24.7%)
|
26(40.0%)
|
|
|
TNM stage
|
|
|
|
6.155
|
0.013
|
|
Ⅰ
|
75(88.2%)
|
47(72.3%)
|
|
|
|
Ⅱ~Ⅳ
|
10(11.8%)
|
18(27.7%)
|
|
|
PDL-1
|
|
|
|
3.824
|
0.051
|
|
<10
|
49(57.6%)
|
27(41.5%)
|
|
|
|
>=10
|
36(42.4%)
|
38(58.5%)
|
|
|
Clinical outcome influenced by PSTPIP1 expression. We searched the GSCA database and generated Kaplan‒Meier curves of high and low expression of PSTPIP1 in KIRC (Fig. 4A). The high expression group had a significantly shorter overall survival (P<0.01), which was also proven by our clinical sample data. Survival analysis of clinical samples showed that the average survival time of the high expression group was 74.58±3.44 months, while that of the low expression group was 80.91±2.37 months (P<0.05, Fig. 4B). Univariate analysis and multivariate analysis were performed to determine the effect of PSTPIP1 protein on KIRC prognosis (Table 2). Univariate analysis showed that tumor size (HR=4.024, 95%CI:1.709-9.471, P<0.05), metastasis (HR=23.486, 95%CI:6.286-87.755, P<0.05), microvascular invasion (HR=4.076, 95%CI:1.995-11.097, P<0.05), Edmondson grade (HR=4.911, 95%CI:2.264-10.650, P<0.05), TNM stage (HR=8.346, 95%CI:3.931-17.722, P<0.05) and PSTPIP1 expression (HR=2.159, 95%CI:1.011-4.610, P<0.05) significantly influenced survival time. Further multivariate analysis indicated that metastasis, grade and TNM stage were independent factors. Although PSTPIP1 expression was not an independent factor, its high expression negatively affected KIRC progression and contributed to poor prognosis.
Table 2 Univariate and Multivariate Cox Regression Survival Analysis of Clinicopathologica Parameters and PSTPIP1 Expression in Patients.
Parameters
|
Univariate Analysis
|
Multivariate Analysis
|
HR
|
95%CI
|
P
|
HR
|
95%CI
|
P
|
Gender
|
0.399
|
0.139-1.151
|
0.089
|
NA
|
Age (yrs.)
|
2.099
|
0.892-4.937
|
0.089
|
NA
|
Size
|
4.024
|
1.709-9.471
|
P<0.05
|
1.532
|
0.532-4.408
|
0.429
|
metastasis
|
23.486
|
6.286-87.755
|
P<0.05
|
4.591
|
1.134-18.581
|
P<0.05
|
Microvascular invasion
|
4.706
|
1.995-11.097
|
P<0.05
|
1.594
|
0.600-0.4.234
|
0.35
|
Edmondson grade
|
4.911
|
2.264-10.650
|
P<0.05
|
2.569
|
1.093-6.039
|
P<0.05
|
TNM stage
|
8.346
|
3.931-17.722
|
P<0.05
|
3.296
|
1.180-9.209
|
P<0.05
|
PDL-1
|
1.932
|
0.892-4.187
|
0.095
|
NA
|
PSTPIP1
|
2.159
|
1.011-4.610
|
P<0.05
|
1.349
|
0.578-3.149
|
0.49
|
Co-expressed genes and pathways correlated with PSTPIP1. We analyzed 533 samples from the TCGA database through the LinkedOmics online tool. There were 8861 genes (red spots, FDR<0.05) positively related to PSTPIP1 and 4905 genes (green spots, FDR<0.05) negatively related to PSTPIP1, as shown in the volcano plot (Fig. 5 A). The heatmaps display the top 50 positively related and negatively related genes (Fig. 5 B, C). The three most positively related genes were ACAP1, CORO1A, and DEF6 (Fig. 5 D, E, F). The three most negatively related genes were SYPL1, CYP51A1, and PTPLAD1 (Fig. 5 G, H, I).
Next, GO (Gene Ontology) and KEGG pathway analyses were performed by GSEA (Gene Set Enrichment Analysis). Coexpressed genes located in the biological process, cellular component, and molecular function categories are listed in Fig. 6(ABC). PSTPIP1 has a clear preference for participating in biological processes: adaptive immune response; regulation of leukocyte activation; cellular defense response; interleukin-1 production; and leukocyte differentiation. KEGG pathway analysis results (Fig. 6D) showed that the top 6 enrichment pathways were cell adhesion molecules (CAMs) (Fig. 6E), natural killer cell-mediated cytotoxicity (Fig. 6F), cytokine‒cytokine receptor interaction (Fig. 6G), osteoclast differentiation (Fig. 6H), Epstein‒Barr virus infection (Fig. 6I), and tuberculosis (Fig. 6J). These results indicated that PSTPIP1 may promote KIRC progression through several immune response pathways.
Protein–protein interaction analysis. The STRING database were used to build up protein-protein interaction network (Fig. 7). The top 10 closest proteins were MEFV, PTPN12, WAS, PTPN18, CD2, FASLG, PTPN22, WASL, PYCARD and PTS.