3.1. Result of Gene Expression Analysis
The present research intended to identify the oncogenic role of DEFB1 (NM_005218.4 for mRNA). Thus, an initial analysis into DEFB1 expressions among various non-neoplastic tissues was carried out in it. By combining the HPA, GTEx, as well as Functions annotation of the mammalian genome 5 (FANTOM5) datasets, it has been determined that DEFB1 has the highest mRNA expression in the salivary gland, which is followed by the kidney and pancreas (Fig. 1A). Furthermore, the single-cell expression result (Fig. 1B) found a high DEFB1 expression level in distal tubular, mucus glandular, and salivary duct cells. At the same time, DEFB1 was highly expressed in various cell lines, including CACO-2, Hep-G2, and OE19 (Fig. 1C).
Figure 1. DEFB1 expression pattern in cancer and adjacent normal tissues. DEFB1 expression level in mRNA (A), single-cell (B), and cell lines (C).
We utilized the TIMER2 website and TCGA data to examine the DEFB1 expression level in diverse cancers. Figure 2A demonstrates that the DEFB1 level was higher in tissues from cholangiocarcinoma (CHOL), kidney chromophobe (KICH), skin cutaneous melanoma (SKCM), esophageal carcinoma (ESCA), lung squamous cell carcinoma (LUSC), and UCEC than in the corresponding normal tissues (P < 0.05). However, DEFB1 expressions from cancer tissues of BRCA, colon adenocarcinoma (COAD), HNSC, kidney renal clear cell carcinoma, kidney renal papillary cell carcinoma, prostate adenocarcinoma, as well as rectum adenocarcinoma (P < 0.001) showed a significant lower level.
We set the normal tissue of the GTEx dataset as controls and demonstrated that DEFB1 levels were different in LAML, Ovarian serous cystadenocarcinoma (OV), Sarcoma (SARC), Testicular germ cell tumors (TGCT), as well as Uterine carcinosarcoma (UCS) with statistical significance (Fig. 2B, P < 0.05).
According to the data obtained from CPTAC, it was observed that there is a significant upregulation of DEFB1 in samples from ovarian cancer, UCEC, LUAD, as well as liver cancer (Fig. 2C, P < 0.001) compared to that in the matched normal tissues. In contrast, the primary tissues of clear cell RCC and HNSC exhibited a relatively lower DEFB1 protein expression in contrast with normal tissues (Fig. 2C, P < 0.001).
This study utilized the “Pathological Stage Plot” module of GEPIA2 to clarify the association of DEFB1 with other cancers, including KICH, OV, pancreatic adenocarcinoma (PAAD) and SKCM (Fig. 3A, P < 0.01).
Figure 2. DEFB1 level in cancer tissues as well as cell lines. (A) DEFB1 levels in different cancers was identified via TIMER2. (*P < 0.05; **P < 0.01; ***P < 0.001). (B) The controls for the LAML, OV, SARC, TGCT, and UCS samples in the TCGA project were established using the corresponding normal tissues sourced from the GTEx database. The box plot data were supplied. (*P < 0.05). (C) The study utilized the CPTAC dataset to clarify the DEFB1 expression in ovarian cancer, clear cell RCC, UCEC, LUAD, HNSC, as well as liver cancer. (***P < 0.001).
3.2. Survival Data
Cases with cancer were classified into two groups, namely high- and low-expression groups, based on DEFB1 expression levels. Subsequently, the correlation of DEFB1 expression with the prognosis of patients with tumors based on the datasets primarily obtained from TCGA. Figure 3B finds that high DEFB1 level could induce poor OS for LUAD and PAAD (P < 0.05). Besides, low DEFB1 level could lead to poor OS for HNSC (Fig. 3B, P = 0.017). Figure 3C concludes that high DEFB1 level could induce poor DFS for CHOL cases (P = 0.027).
Figure 3. Association of DEFB1 expression with prognosis in TCGA data. (A) The study used the TCGA data to investigate the association of the DEFB1 level with the different stages of KICH, OV, PAAD as well as SKCM. Log2 (TPM + 1) was used for log-scale. The present research applied the GEPIA2 tool to obtain results on overall survival (B) as well as disease-free survival (C). The positive survival map together with Kaplan-Meier curves were presented.
3.3. Genetic Alteration Data
The condition of DEFB1 expression was obtained from the TCGA cohorts. Figure 4A demonstrates that patients with the primary type Liver hepatocellular carcinoma (LIHC) with “deep deletion” had the highest alteration frequency of DEFB1 (> 6%). In stomach adenocarcinoma (STAD), the predominant form of CNA is characterized by "amplification", exhibiting an alteration frequency exceeding 3%. SKCM cases with the alteration frequency of 1% had copy number mutation of DEFB1 (Fig. 4A). The types, sites, as well as case number of the DEFB1 genetic alteration are shown in Fig. 4B. The result indicated missense mutation to be the primary alteration type. In one case of UCEC and one case each of cervical squamous cell carcinoma & endocervical adenocarcinoma (Fig. 4B), an H34D/N alteration in the Defensin_beta domain led to a missense or DEFB1 gene mutation, causing a subsequent change in the DEFB1 protein. The DEFB1 protein's 3D structure is visually illustrated in Fig. 4C.
Figure 4. Mutation characteristics associated with DEFB1. We applied the cBioPortal tool for the purpose of elucidating the mutation characteristics pertaining to DEFB1. The mutation type (A), mutation site (B), and the mutation site with the highest alteration frequency (H34D/N) are displayed. We also display its 3D structure (C).
3.4. Data of Immune Infiltration
To analyze the underlying association of immune cell infiltration levels with the expressions of DEFB1 across various cancer types in TCGA, we employed the TIMER, EPIC, QUANTISEQ, XCELL, MCPCOUNTER, CIBERSORT, as well as CIBERSORT-ABS algorithms. A positive association of the DEFB1 levels with the estimated infiltration values of cancer-associated fibroblasts among the LIHC and thyroid carcinoma (THCA) but concluded a negative relationship for COAD, HNSC, and STAD with statistical significance was observed (Fig. 5). The result showed a statistical positive association of the infiltration degree of neutrophil with DEFB1 for bladder carcinoma (BLCA), DLBC, LUSC, PAAD, and UCEC (Fig. 6). The scatterplot data are presented in Figs. 5–6. For instance, utilizing the CIBERSORT algorithm, a positive association of DEFB1 expression level in BLCA with neutrophil infiltration level was observed(Fig. 6, cor = 0.247, P = 1.62e-06)
Figure 5. Correlation of DEFB1 level with infiltration degree of cancer-associated fibroblasts. Different algorithms were conducted to investigate the association of DEFB1 with the infiltration degree of fibroblasts.
Figure 6. Association of DEFB1 with the infiltration degree of neutrophil. Different algorithms were conducted to clarify the relationship of DEFB1 level with the infiltration degree of neutrophil in TCGA tumors.
3.5. DEFB1-related Partners
In an effort to delve into the molecular mechanisms behind DEFB1 gene's role in tumorigenesis, this research aimed to clarify its related proteins and genes. The study utilized GEPIA2 to find out the top 100 genes that related to DEFB1 level. Figure 7 reveals that the DEFB1 level was positively related to KLK1 ( kallikrein 1) (R = 0.68), BSND (barttin CLCNK type accessory subunit beta) (R = 0.60), FXYD2 (FXYD domain containing ion transport regulator 2) (R = 0.60), EMX1 (empty spiracles homeobox 1) (R = 0.59), and CLCNKB (empty spiracles homeobox chloride voltage-gated channel Kb) (R = 0.59) genes (all P < 0.001). Among most of specific cancer types, the heatmap data exhibited a positive association of DEFB1 with the aforementioned 5 genes.
Figure 7. DEFB1-related gene analysis. The GEPIA2 approach was conducted to get the top 100 genes related with DEFB1 in TCGA and explored the association of DEFB1 expressions with specific targeting genes, such as KLK1, BSND, FXYD2, EMX1, and CLCNKB. The heatmap data for cancer types are displayed.