Expression profiles of AKR1Cs in HCC
To investigate values of AKR1Cs in HCC patients, we first analyzed expression of AKR1Cs by CCLE, ONCOMINE and UALCAN databases. CCLE analysis demonstrated that mRNA expression of four members in HCC cell lines all ranked forefront levels among the common cancer cell lines, moreover AKR1C1 and AKR1C4 ranked the top level (Fig. 1a). Analysis by ONCOMINE database showed that AKR1C3 mRNA level was significantly higher in cancerous tissue than in normal samples, however AKR1C4 mRNA expression was lower in HCC tissues (Additional file 1: Figure S1a). Meta-analysis of multiple datasets indicated significantly higher levels of AKR1C1/2/3 in HCC than in normal tissues (Additional file 1: Figure S1b). In Roessler Liver 2 dataset [18], AKR1C3 over-expression was found in HCC tissues compared with normal tissues with a fold change of 3.438 (p = 3.86E-71) (Additional fle 2: Figure S2a), Wurmbach Liver dataset [19] also showed AKR1C3 was over-expressed in HCC (Additional file 2: Figure S2b). AKR1C2 was over-expressed with a fold change of 1.543 (p = 4.53E-4) in Wurmbach Liver dataset (Additional file 2: Figure S2c).
To further explore mRNA expression levels of AKR1Cs in HCC, we used UALCAN database, whose data resource was totally different from ONCOMINE, to conduct this analysis. As shown in Fig. 1b, mRNA expressions of AKR1C1/2/3 were proved to be significantly higher in tumor tissues than in normal samples (all p < 0.05).
Correlation of AKR1Cs mRNA level with clinical indicators in HCC patients
Combined with above results, we concluded that AKR1C1/2/3 was significantly high-expressed in HCC tissues. Then we investigated the relationship between respective expression level and clinical indicators in HCC patients. Sub-group analysis of multiple clinic pathological features of HCC samples in UALCAN database consistently showed higher transcription level of AKR1C1/2/3 in HCC patients than in healthy human based on gender, age and tumor stage (Fig. 1c, d, e). Further analyzing the results of mRNA expression with tumor grade, we found that transcription levels of AKR1C1/2/3 were apparently correlated with tumor grade in HCC patients, patients with higher tumor grade tend to have higher expression of AKR1C1/2/3 (Fig. 1f).
Relationship of expression of AKR1Cs and immune infiltration and T cell exhaustion in HCC
The correlation between AKR1Cs expression and immune invasion in HCC was evaluated using Timer database in this study. The results showed that the infiltration levels of CD4+ T cells were negatively correlated with the expression of all AKR1C members (Fig. 2, all p < 0.05), and levels of infiltrated macrophages were also negatively correlated with AKR1C1/2/4 expression (Fig. 2).
Next, we used the GEPIA database to identify the relationship between AKR1Cs expression and T cell exhaustion markers including PD-1, LAG3, GZMB and CTLA4 in tumor and normal tissues. Our results showed that there was a negative correlation of AKR1C2/4 and PD-1 in tumor tissues (p < 0.05, Additional file 3: Table S1), but no significant correlations between remaining members and other markers.
Elevated AKR1C1/2/3 Expression Predicted Poor Prognosis In HCC Patients
To analyze the prognosis values of distinct AKR1C members in HCC patients, Kaplan-Meier plotter was used and the results showed that patients with high mRNA level of AKR1C1 (hazard ratio (HR) = 1.78, 95% confidence interval (CI): 1.25–2.52, and p = 0.0012), AKR1C2 (HR = 1.51, 95% CI: 1.04–2.18, and p = 0.028) and AKR1C3 (HR = 1.69, 95% CI: 1.2–2.4, and p = 0.0027) had poor OS (Fig. 3a). However high mRNA expression of AKR1C4 (HR = 0.68, 95% CI: 0.47–0.97, and p = 0.035) was associated with favorable OS (Fig. 3a). Integration analysis of multiple members showed that high combinatory mRNA expression of AKR1C1/2/3 (HR = 1.88, 95% CI: 1.32–2.67, and p = 4E-04) or all members (HR = 1.86, 95% CI: 1.3–2.65, and p = 0.00053) was significantly associated with poor OS in HCC patients (Fig. 3a). Similar results were observed when analyzing PFS, RFS and DSS (Fig. 3b, c, d). Taken together, these results indicated that high mRNA expression of AKR1C1/2/3 was significantly correlated with poor prognosis in HCC patients and AKR1C1/2/3 could be viewed as significant risk indicators.
Validation Of AKR1C1/2/3 Expression On OS In HCC Patients
Data of clinical indicators and mRNA expression of AKR1Cs in HCC patients was downloaded from the TCGA database through the Firebrowse website (http://firebrowse.org/api-docs/) when conducting Cox survival regression analyses. After screening by professional assessment and data integrity, we included 134 patients with complete data and 16 clinical indicators in this study (Table 1). The results of univariate and multivariate analyses were summarized in Table 2. In univariate analysis, total bilirubin (TB) (HR = 42.737, 95% CI: 9.568-190.886, and p < 0.001) and surgical margin (HR = 4.935, 95% CI: 1.920-12.685, and p = 0.001) were identified as independent risk factors of patient OS. Multivariate analysis revealed that albumin (HR = 1.350, 95% CI: 1.064–1.714, and p = 0.013), prothrombin time (PT) (HR = 1.140, 95% CI: 1.047–1.241, and p = 0.002), TB (HR = 5859.486, 95% CI: 407.319-84291.531, and p < 0.001), tumor necrosis (HR = 1.054, 95% CI: 1.002–1.109, and p = 0.043), surgical margin (HR = 12.774, 95% CI: 3.692–44.196, and p < 0.001) together with mRNA levels of AKR1C1/2/3 (all p < 0.05) were significantly associated with patient OS.
Genomic alterations and biological interaction network of AKR1Cs in HCC
Next, we used cBioPortal, which was based on sequencing data from the TCGA database to explore genetic alterations of AKR1Cs and their associations with prognostic indicators in HCC patients. As shown in Fig. 4a, AKR1Cs were altered in 70 of 370 (19%) patients and AKR1C2 ranked the highest level (the mutation rate was 11%). Among these alterations, 54 patients had mRNA upregulation (14.59%), 7 cases had amplification (1.89%) and only 2 cases had deep deletion (0.54%) (Additional file 4: Table S2). To further investigate the roles of genomic alterations of AKR1Cs in HCC, we conducted survival analysis and the results showed that patients with AKR1Cs alterations had poor OS and PFS (Fig. 4b, c, all p < 0.05), indicating that genomic alterations of AKR1Cs had significant impacts on patient prognosis in HCC.
Table 1
Clinicopathological variables of 134 HCC specimens with complete data
variables | HCC patients (N = 134) |
Gender ( Male/female) | 91/43 |
Age (years, Mean ± SD) | 58.65 ± 13.42 |
Weight(kg, Mean ± SD) | 71.29 ± 16.30 |
Adjacent tissue inflammation | |
none | N = 58 |
mild | N = 62 |
severe | N = 14 |
Albumin (g/L, Median) | 3.95(0.20–5.10) |
Childpugh stage | |
A | N = 122 |
B | N = 12 |
AFP (ng/ml, Median) | 9(1-2035000) |
Platelet (10e9/L, Median) | 198.5(69-334000) |
PT (s, Median) | 1.1(0.8–19) |
TB (µmol/L, Median) | 1.2(1-1.5) |
Fibrotic score | |
no fibrosis | N = 42 |
portal fibrosis | N = 18 |
fibrous speta | N = 19 |
nodular formation and incomplete cirrhosis | N = 5 |
established cirrhosis | N = 50 |
Histologic grade | |
g1 | N = 13 |
g2 | N = 68 |
g3 | N = 48 |
g4 | N = 5 |
Vascular invasion (yes/no) | 40/94 |
Tumor weight (g, Median) | 150(50-1400) |
Tumor necrosis (%,Median) | 5(0–30) |
Surgical margin (positive/negative) | 6/128 |
HCC hepatocellular carcinoma, AFP alpha-fetoprotein, PT prothrombin time, TB total bilirubin, SD standard deviation |
Table 2
Prognostic factors associated with OS in 134 HCC specimens with complete data
Variables | Univariate analysis | Multivariate analysis |
HR | 95% CI | P value | HR | 95% CI | P value |
Gender | | | | | | |
Age(years) | | | | | | |
Weight(kg) | | | | | | |
Adjacent tissue inflammation | | | | | | |
Albumin (g/L) | | | | 1.350 | 1.064–1.714 | 0.013* |
Childpugh stage | | | | | | |
AFP (ng/ml) | | | | | | |
Platelet (10e9/L) | | | | | | |
PT (s) | | | | 1.140 | 1.047–1.241 | 0.002* |
TB (µmol/L) | 42.737 | 9.568-190.886 | 0.000* | 5859.486 | 407.319-84291.531 | 0.000* |
Fibrotic score | | | | | | |
Histologic grade | | | | | | |
Vascular invasion | | | | | | |
Tumor weight | | | | | | |
Tumor necrosis (%) | | | | 1.054 | 1.002–1.109 | 0.043* |
Surgical margin | 4.935 | 1.920-12.685 | 0.001* | 12.774 | 3.692–44.196 | 0.000* |
AKR1C1 | | | | 1.000 | 1.000–1.000 | 0.023* |
AKR1C2 | | | | 1.000 | 1.000–1.000 | 0.001* |
AKR1C3 | | | | 1.000 | 1.000–1.000 | 0.029* |
AKR1C4 | | | | | | |
Variables with p < 0.05 were marked with asterisk (*) |
OS over survival, HCC hepatocellular carcinoma, AFP alpha-fetoprotein, PT prothrombin time, TB total bilirubin |
We then planned to study the biological interaction network of AKR1Cs in HCC using the Network tool in cBioPortal, and Fig. 4d showed the constructed network of neighboring genes associating with AKR1Cs mutations. The most frequent alterations were RDH10 (21.1%) and ADH5 (6.8%) among these neighboring genes (Additional file 5: Table S3). Functions of AKR1Cs and the frequently altered neighboring genes were enriched by g:Profiler website (Additional file 6: Table S4). Results of enriched GO terms indicated that these genes encode proteins localized mainly in endoplasmic reticulum membrane, nuclear outer membrane and endoplasmic reticulum part (Fig. 4e). These proteins are primarily involved in oxidation-reduction process, cellular hormone metabolic process and organic hydroxy compound metabolic process (Fig. 4f), while they were also associated with oxidoreductase activity and steroid dehydrogenase activity (Fig. 4g). In KEGG analysis, it was suggested that retinol metabolism, steroid hormone biosynthesis, metabolic pathway and fatty acid degradation pathway (Fig. 4h) all showed enrichments, which indicated the possible pathways of AKR1Cs mutation in HCC.
Construction of PPI network and enrichment analysis of AKR1Cs functional networks in HCC
PPI network was constructed using STRING database, and the results indicated that there was a close positive correlation between any two of AKR1C1/2/3 members. However, AKR1C4 is much less relevant with remaining members (Fig. 4i-l and Additional file 7: Table S5).
The LinkedOmics database, containing mRNA sequencing data of 371 HCC patients in the TCGA was used to analyze co-expression genes correlated with AKR1Cs in HCC. As shown in Fig. 5a, volcano plot indicated genes with significant positive and negative correlations with AKR1C1 (false discovery rate [FDR] < 0.01). And the top 3 positively correlated genes with AKR1C1 were showed in Additional file 8: Table S6, they were AKR1C2 (positive rank #1, Pearson correlation = 0.88, p = 1.16e–119), AKR1C3 (Pearson correlation = 0.66, p = 4.43e–48) and ALDH1L1 (Pearson correlation = 0.66, p = 5.45e–48). The heat map showed the 50 significant gene sets positively and negatively correlated with AKR1C1 (Fig. 5a). The same method is used to analyze AKR1C2/3/4, and the results were shown in Fig. 5b, c, d, Additional file 8: Table S6 and Additional file 9: Table S7. All these results reflected that AKR1C1/2/3 had a strong positive correlation with each other, indicating the 3 members may play a synergistic role in function regulation. We then used gene set enrichment analysis (GSEA) to perform GO term and KEGG analyses and found that significant genes differentially expressed in correlation with AKR1C1 were located mainly in the mitochondria, ribosome and respiratory chain, while they were mainly involved in coenzyme metabolic process, cellular amino acid metabolic process and fatty acid metabolic process. At the same time, they play important roles in the structural constituent of ribosome, oxidoreductase activity and electron transfer activity (Fig. 6a). KEGG pathway analysis showed they were mainly enriched in ribosome, oxidative phosphorylation and carbon metabolism pathways (Fig. 6a). Similarly, we did similar analysis for AKR1C2/3/4, and results were shown in Fig. 6b, c, d and Additional file 10: Table S8.