The expression levels of ALKBH5 in pan-cancer
To determine the role of ALKBH5 in pan-cancer, we first tested the expression levels of ALKBH5 in human cancer and normal tissues. The results showed that ALKBH5 mRNA was higher in ACC (adrenocortical carcinoma), BRCA (breast invasive carcinoma), CESC (cervical squamous cell carcinoma and endocervical adenocarcinoma), CHOL (cholangiocarcinoma), COAD (colon adenocarcinoma), ESCA (esophageal carcinoma), GBM (glioblastoma multiforme), HNSC (head and neck squamous cell carcinoma), KIRC (kidney renal clear cell carcinoma), LAML (acute myeloid leukemia), LGG (brain lower grade glioma), LIHC (liver hepatocellular carcinoma), LUSC (lung squamous cell carcinoma), LUAD (lung adenocarcinoma), OV (ovarian serous cystadenocarcinoma), PAAD (pancreatic adenocarcinoma), PRAD (prostate adenocarcinoma), SKCM (skin cutaneous melanoma), STAD (stomach adenocarcinoma), TGCT (testicular germ cell tumors), THCA (thyroid carcinoma) and UCS (uterine carcinosarcoma) tissues than that in normal tissues, but in KIRP (kidney renal papillary cell carcinoma), READ (rectum adenocarcinoma) and UCEC (uterine corpus endometrial carcinoma) had opposite results (Figure 1A). Moreover, there was no difference between normal and cancer tissues in BLCA (bladder urothelial carcinoma) and KICH (kidney chromophobe) (Figure 1A). Similarly, ALKBH5 protein was higher in breast cancer, OV, KIRC, lung cancer, glioblastoma and liver cancer, whereas lower in UCEC and pancreatic cancer (Figure 1B).
Prognostic value of ALKBH5 in pan-cancer
To explore the prognostic value of ALKBH5 in cancers, we analyzed the relationship between the expression levels of ALKBH5 and OS in 33 cancers and found the higher expression level of ALKBH5 was a risk factor of OS in BLCA, GBM, KICH, LAML and LGG, while a low-risk factor in ESCA, OV and PAAD (Figure 2A). Considering that there may be factors other than tumor-caused death, we also analyzed the correlation between the ALKBH5 expression and DSS. And we found higher ALKBH5 indicated a high risk of DSS in GBM, KICH and LGG and a low risk in OV and KIRC (Figure 2B). Also, higher ALKBH5 showed a high risk of PFI in ACC, KICH, LGG and LUSC, but a low risk in PAAD (Figure 2C). Moreover, higher ALKBH5 showed a high risk of DFI in ACC and LUSC (Figure 2D).
Meanwhile, we also tested the correlation between ALKBH5 expression and OS, and the results showed that the highly expressed ALKBH5 has a shorter OS time in BLCA, KICH, LAML, LGG and UVM, but a longer OS time in CESC (Figure 2E). Moreover, highly expressed ALKBH5 has a shorter DFS time in ACC and LGG (Figure 2F).
Further, we explored the correlation between ALKBH5 expression and clinical features such as pathological stage, T stage and histological type. The results showed that, for pathological stage, the expression of ALKBH5 was significantly downregulated in THCA, KIRC, SKCM, TGCT and OV (Figure 3A). With the increase of T stage, ALKBH5 was upregulated in STAD, while downregulated in THCA and KIRC (Figure 3B). Intriguingly, ALKBH5 expression was higher in endometrioid than serous UCEC. And in THYM, both type A and B have higher ALKBH5 expression compared to type C (Figure 3C).
ALKBH5 Expression is correlated with Immune Infiltration in pan-caner
Immunotherapy as one of the effective treatments for cancers, such as cell immunotherapy and checkpoint treatment strategy has become the focus of researchers18. Infiltration of immune cells in the cancer environment means that immune cells move from the blood to the cancer tissue and begin to play their roles. These immune cells can be separated and is closely related to the clinical results19, indicating they may serve as drug targets20. Therefore, we firstly analyzed the correlation between these immune cells and OS. Results showed these immune cells were remarkably associated with OS in various cancers (Table S1). Then, we found ALKBH5 expression was remarkably associated with purity in various cancers (Table 1). Next, the correlation between ALKBH5 expression and B cell, CD4+T cell. CD8+T cell, neutrophil, macrophage, dendritic cell was investigated respectively. Surprisingly, ALKBH5 expression remarkably correlated with these immune cells (Table S2), especially in COAD, KIRC and LGG
Table 1
The relationship between ALKBH5 expression and purity, homologous recombination deficiency (HRD) and stemness scores (DNAss) in pan-cancer.
Cancer type
|
Purity
|
HRD
|
DNAss
|
Cor
|
P
|
Cor
|
P
|
Cor
|
P
|
ACC
|
0.310
|
0.006
|
0.250
|
0.030
|
0.040
|
0.760
|
BLCA
|
-0.020
|
0.680
|
0.130
|
0.010
|
-0.140
|
0.005
|
BRCA
|
0.160
|
<0.001
|
-0.160
|
<0.001
|
-0.050
|
0.140
|
CESC
|
0.130
|
0.030
|
-0.110
|
0.070
|
0.030
|
0.550
|
CHOL
|
-0.020
|
0.920
|
-0.110
|
0.540
|
0.420
|
0.010
|
COAD
|
-0.310
|
<0.001
|
-0.110
|
0.050
|
-0.210
|
<0.001
|
DLBC
|
-0.170
|
0.270
|
-0.030
|
0.840
|
-0.050
|
0.750
|
ESCA
|
0.190
|
0.020
|
0.150
|
0.060
|
-0.030
|
0.720
|
GBM
|
0.060
|
0.500
|
0.040
|
0.630
|
-0.010
|
0.930
|
HNSC
|
0.130
|
0.004
|
0.190
|
<0.001
|
0.070
|
0.130
|
KICH
|
-0.080
|
0.550
|
0.370
|
0.002
|
-0.170
|
0.180
|
KIRC
|
0.030
|
0.490
|
0.100
|
0.030
|
0.040
|
0.510
|
KIRP
|
0.090
|
0.130
|
-0.140
|
0.020
|
-0.100
|
0.100
|
LAML
|
0.010
|
0.910
|
-0.200
|
0.040
|
0.110
|
0.160
|
LGG
|
-0.070
|
0.130
|
0.130
|
0.003
|
0.290
|
<0.001
|
LIHC
|
0.110
|
0.030
|
0.090
|
0.080
|
-0.040
|
0.480
|
LUAD
|
0.110
|
0.010
|
0.060
|
0.220
|
0.007
|
0.880
|
LUSC
|
0.270
|
<0.001
|
0.070
|
0.130
|
0.170
|
0.001
|
MESO
|
0.080
|
0.460
|
0.080
|
0.470
|
-0.010
|
0.910
|
OV
|
0.010
|
0.770
|
0.030
|
0.500
|
0.500
|
0.210
|
PAAD
|
0.160
|
0.040
|
-0.130
|
0.110
|
-0.030
|
0.720
|
PCPG
|
-0.090
|
0.270
|
0.020
|
0.830
|
-0.080
|
0.300
|
PRAD
|
-0.120
|
0.007
|
-0.040
|
0.420
|
-0.020
|
0.600
|
READ
|
-0.310
|
0.003
|
-0.120
|
0.250
|
-0.150
|
0.160
|
SARC
|
0.270
|
<0.001
|
0.300
|
<0.001
|
0.030
|
0.640
|
SKCM
|
0.010
|
0.900
|
-0.260
|
0.010
|
0.030
|
0.790
|
STAD
|
0.009
|
0.850
|
-0.030
|
0.530
|
-0.010
|
0.860
|
TGCT
|
-0.020
|
0.830
|
-0.400
|
<0.001
|
0.110
|
0.170
|
THCA
|
0.140
|
0.004
|
0.090
|
0.060
|
-0.230
|
<0.001
|
THYM
|
-0.040
|
0.660
|
-0.200
|
0.050
|
-0.210
|
0.020
|
UCEC
|
0.150
|
0.040
|
-0.230
|
0.002
|
0.020
|
0.820
|
UCS
|
0.150
|
0.280
|
0.070
|
0.630
|
0.140
|
0.300
|
UVM
|
-0.390
|
<0.001
|
-0.220
|
0.060
|
0.200
|
0.080
|
In the TME, ESTIMATE algorithm can quantify immune and stromal components in the cancer21. We analyzed the correlation between ALKBH5 expression and immune and stromal scores and found that the expression of ALKBH5 was significantly correlated with these three scores (Table S3), especially negatively in THCA and ACC, but positively in COAD and UVM (Figure 5).
As mentioned above, the immunoregulatory gene functions importantly in cancers, including chemokines, receptors, major histocompatibility complex (MHC), immune inhibitors and immune stimulators. Therefore, the correlation between these immunoregulatory genes and ALKBH5 expression in cancers was performed. ALKBH5 showed significantly correlation with immunoregulatory genes in various cancers (Figure 6).
The correlation between ALKBH5 expression and tumor mutation in pan-cancer
Tumor mutation is the pivotal factor affecting tumor prognosis22. We first analyzed the mutation of ALKBH5 in cancers. It was found that ALKBH5 has a missense mutation rate from 0.2% to 1.4% in BLCA, BRCA, CESC, COAD, ESCA, GBM, HNSC, KIRP, LGG, LIHC, LUAD, LUSC, PAAD, PRAD, SARC, STAD and UCEC, however, there was no detected missense mutation in other cancers (Fig 7A). Then, the correlation between ALKBH5 expression and CNV was explored in cancers and the significance was shown in BLCA, BRCA, CESC, ESCA, HNSC, LIHC, LUAD, LUSC, OV, PAAD, PRAD, SARC, STAD, UCEC and UCS (Fig 7B). Mutations in cancer cells can cause TMB, MSI, neoantigen and HRD. Thus, we firstly tested the correlation between ALKBH5 expression and TMB and the remarkable correlation presented in BRCA, COAD, DLBC, ESCA, LGG, PRAD, SARC and THCA (Table 2). As for MSI, the significant correlation existed in COAD, DLBC, KIRC, LUAD, LUSC, PRAD, SARC, STAD and THCA (Table 2). Besides, tumor mutations can also produce new antigens, which in turn affect the patient's prognosis. Intriguingly, ALKBH5 expression was significantly correlated with the count of neoantigens in COAD and UCEC (Table 2). Further, ALKBH5 and HRD showed a significant correlation in ACC, BLCA, BRCA, HNSC, KICH, KIRC, KIRP, LAML, LGG, SARC, SKCM, TGCT and UCEC (Table 1).
Table 2
The relationship between ALKBH5 expression and tumor mutational burden (TMB), microsatellite instability (MSI) and neoantigen in pan-cancer.
Cancer type
|
TMB
|
MSI
|
Neoantigen
|
Cor
|
P
|
Cor
|
P
|
Cor
|
P
|
ACC
|
0.150
|
0.190
|
-0.030
|
0.800
|
0.070
|
0.590
|
BLCA
|
-0.030
|
0.600
|
0.050
|
0.310
|
0.030
|
0.590
|
BRCA
|
-0.190
|
<0.001
|
-0.010
|
0.710
|
0.040
|
0.300
|
CESC
|
-0.050
|
0.380
|
0.050
|
0.380
|
0.080
|
0.210
|
CHOL
|
0.100
|
0.570
|
0.190
|
0.260
|
-0.190
|
0.310
|
COAD
|
0.340
|
<0.001
|
0.360
|
<0.001
|
0.340
|
<0.001
|
DLBC
|
-0.340
|
0.040
|
-0.500
|
<0.001
|
0.002
|
0.990
|
ESCA
|
-0.180
|
0.010
|
0.020
|
0.830
|
-
|
-
|
GBM
|
0.070
|
0.420
|
0.110
|
0.170
|
0.040
|
0.690
|
HNSC
|
-0.090
|
0.050
|
0.005
|
0.910
|
-0.020
|
0.600
|
KICH
|
0.160
|
0.210
|
-0.050
|
0.680
|
0.070
|
0.660
|
KIRC
|
0.010
|
0.800
|
0.120
|
0.030
|
0.030
|
0.620
|
KIRP
|
-0.040
|
0.480
|
0.030
|
0.650
|
-0.020
|
0.730
|
LAML
|
-0.130
|
0.150
|
0.010
|
0.870
|
-
|
-
|
LGG
|
0.150
|
<0.001
|
-0.050
|
0.280
|
-0.003
|
0.950
|
LIHC
|
-0.060
|
0.240
|
0.020
|
0.640
|
0.040
|
0.470
|
LUAD
|
0.020
|
0.600
|
0.100
|
0.020
|
0.040
|
0.390
|
LUSC
|
-0.060
|
0.190
|
0.190
|
<0.001
|
0.030
|
0.520
|
MESO
|
0.130
|
0.240
|
-0.040
|
0.730
|
0.020
|
0.900
|
OV
|
-0.010
|
0.810
|
0.030
|
0.600
|
-
|
-
|
PAAD
|
-0.210
|
0.005
|
-0.030
|
0.670
|
0.020
|
0.850
|
PCPG
|
-0.010
|
0.860
|
0.130
|
0.090
|
-0.070
|
0.570
|
PRAD
|
-0.150
|
<0.001
|
-0.090
|
0.040
|
-0.060
|
0.260
|
READ
|
-0.090
|
0.420
|
0.040
|
0.700
|
0.050
|
0.680
|
SARC
|
0.220
|
<0.001
|
0.170
|
0.006
|
0.020
|
0.780
|
SKCM
|
0.130
|
0.190
|
0.120
|
0.220
|
0.060
|
0.600
|
STAD
|
0.040
|
0.410
|
0.160
|
0.001
|
-
|
-
|
TGCT
|
-0.150
|
0.070
|
-0.050
|
0.580
|
0.090
|
0.370
|
THCA
|
-0.210
|
<0.001
|
-0.170
|
<0.001
|
-0.100
|
0.170
|
THYM
|
-0.030
|
0.770
|
0.005
|
0.950
|
-0.090
|
0.470
|
UCEC
|
0.150
|
0.050
|
0.120
|
0.100
|
0.200
|
0.010
|
UCS
|
0.130
|
0.350
|
0.260
|
0.050
|
0.180
|
0.220
|
UVM
|
-0.210
|
0.070
|
0.150
|
0.180
|
-0.070
|
0.670
|
The correlation between ALKBH5 expression and methyltransferase in pan-cancer
Methylation is an important way of epigenetic regulation in organisms and can be divided into DNA and RNA methylation. ALKBH5 serves as a demethylation regulator of RNA, thus we analyzed the correlation between ALKBH5 and genes regulating RNA methylation and a significant correlation was found in most cancers (Figure 8A). And DNA methylation can affect m6A modification by modulating m6A demethylase gene expression23. To further clarify the role of ALKBH5 in cancers, the correlation between ALKBH5 and DNA methyltransferase was performed and there showed a significant correlation between ALKBH5 and DNA methyltransferase in various cancers (Figure 8B). In addition, it is reported that methylation is involved in the regulation of cell stemness, which might regulate immunotherapy24. And we found ALKBH5 expression was correlated with DNAss in BLCA, CHOL, COAD, LGG, LUSC, THCA and THYM (Table 1).