Ornithine decarboxylase (ODC) plays an important role in polyamine biosynthesis which interrelated with many cellular processes such as proliferation, differentiation and apoptosis[22]. Over-accumulation of ODC may stimulate tumorigenesis and could be detected in many epithelial cancers like colon, skin, prostate. As universally demonstrated in numerous studies, antizyme especially Ornithine decarboxylase antizyme1 (OAZ1) could suppress tumor-growth through promoting degradation of ODC[23, 24].
Similar to OAZ1, OAZ2 inhibits the transport of polyamine via binding directly to ODC[25] and can serve as a tumor suppressor in gastric cancer[14] and neuroblastoma[12]. Cho LY et al. demonstrated that OAZ2 rs7403751 showed an obvious decrease in gastric cancer risk under high concentration of daidzein[14]. He H et al. confirmed that OAZ2 could augment OAZ1’s function of maintaining steady state of the follicle through inhibiting polyamine biosynthesis[26]. Li Y et al. proved that OAZ2 was identified as direct downstream target of tumor-suppressor miR-34a and overexpression of OAZ2 could save the chemosensitivity in colon cancer which impaired by deficiency of miR-34a[13]. However, little research has been carried out about the prognostic roles of OAZ2 in CRC.
In this research, we firstly reported the relationship between the low expression of OAZ2 and the poor prognosis in COAD patients. OAZ2 was found expressed lower in tumor tissue than in normal tissue and it was significantly correlated with OS. Our study systematically analyzed the RNA-seq data downloaded from the TCGA database in COAD and divided these patients into two sets in accordance with the medium-level expression of OAZ2: low- or high-level groups. Uni- and multivariate Cox regression analysis were executed to indicate that gender, stage, M and the expression level of OAZ2 all could independently worked as prognostic factors for COAD patients.
Owing to the advantages of user convenience and superiority over traditional diagnostic criteria, nomogram model has gradually become a new method for prognosis of tumor[27, 28]. Wu J et al. established a nomogram which based on seven variables including factors like clinicopathological, demographic and it had been proved to be correlated with the overall survival of low-grade endometrial stromal sarcoma patients[29]. Zeng Q et al. build a nomogram prognosis model and validated that it possessed more brilliant capabilities of predicting the OS than existing models we had for breast malignant tumor patients[30]. In our research, we established a predictive model of nomogram vividly on the basis of OAZ2 expression level and connected clinicopathological parameters such as age, gender, race, stage, T, M, N. At the same time, the AUCs of 1-, 3- and 5-years survival rates and the calibration curves value were calculated for assessment and we could find the model of prognosis nomogram we constructed working definitely well.
GSEA as one useful means of revealing the difference in survival was performed by us in this article to find the OAZ2 related signaling pathways between the OAZ2 high-expression level and low-expression level groups[31]. Two signaling pathways including cardiac muscle contraction and oxidative phosphorylation showed significant association with low-OAZ2 phenotype. As previous researches have shown that oxidative phosphorylation (OXPHOS) and glycolysis could provide critical ATP which needed by tumor cells in proliferation process[32]. Proved by Sun X and Vellinga TT, OXPHOS had strong capacity in increasing the malignancy of CRC and also could raise drug resistance of CRC[33]. Wu Z et al. certificated that OMA1 played a major role in coordinating glycolysis and oxidative phosphorylation and promoting the progression of CRC under Hypoxic environment[34]. Consistent with our research that OXPHOS could serve as significant signaling pathway in colorectal cancer proliferation. Qi L et al. found that three signaling pathways including cellular respiration, electron transfer chain and oxidative phosphorylation were closely related to low-ITGBL group in colorectal cancer via usage of GSEA[35]. Mahdevar M et al. proved that LncRNA SRA could act as a tumor suppressor in CRC through the oxidative phosphorylation pathway[36]. Liu YD et al. demonstrated that Let-7a could inhibit OXPHOS pathway through SNAP23 thus suppressing the progression of colorectal cancer[37].
Tumor mutational burden (TMB) had been proved by previous studies that it could act as independent response indicator of immune checkpoint inhibitors (ICPIs)’s treatment effect[38] and microsatellite instability (MSI) was also certificated that it could play a role in immunotherapy as a predictive target[39]. In our study, we analyzed the connection between OAZ2 expression and MSI, TMB, tumor neoantigen burden (TNB) through utilizing the pearson’s method and there existed strong contact among OAZ2 and MSI, TMB in COAD patients without TNB. We also had verified the association of OAZ2 expression and tumor immune infiltration levels, tumor environment such as Purity, B cell, CD8 + T cell, CD4 + T cell, Macrophage, Neutrophil, Dendritic cell, ESTIMATEScore, ImmuneScore, Stromal Score, the results showed there existed close-knit between them. And we also confirmed closely relationships in COAD patients between OAZ2 and immune checkpoint molecules, immune cell pathways such as BTLA, CD27, CD274, CD86, HAVCR2, ICOS, LAIR1, TNFRSF8, VSIR, Activated B cell, Activated CD4 T cell, Central memory CD4 T cell, Effector memeory CD4 T cell, Gamma delta T cell, Immature dendritic cell, Natural killer cell, Type1 T helper cell and so on. Finally, we came to the conclusion that OAZ2 had an intimate relationship with immunity.
Overall, it might be our first time to probe the relationship between expression level of OAZ2 and its effect on COAD patients. OAZ2 proved to be a reliable landmark for prognosis indicated by uni- and multivariate cox hazard regression analyses. Then, OAZ2 was also found closely related with oxidative phosphorylation pathway via GSEA and intimately connected with immunity via MSI, TMB. We successfully build a model for survival prognosis called nomogram which based on OAZ2. However, there also existed limitations in this research. To first, it seemed to be insufficient and limited to obtain clinical information from TCGA dataset barely, with absent information of treatment too. To second, we just paid attention on bioinformatic analysis of OAZ2 in this article while lacking validation of experiment. Last but not the least, it would be the further target for us to verify the conclusion through implementing in vivo and in vitro experiments.