Exploring The Potential Value Of CSMD2 And SIRT1 In Tumors By Pan-cancer Analysis And Research On The Role Of SIRTs In Gastric Cancer

Objective:Cancer is a serious threat to human health and brings a heavy burden to society and families.Therefore,early diagnosis,effective treatment,and prognosis have always been the focus of research.Our study aimed to find valuable biomarkers for tumors by bioinformatics methods and analyzed the role of SIRTs in gastric cancer.Methods:1.Exploring the potential value of CSMD2 and SIRT1 in tumors by pan-cancer analysis,including expression,prognosis,immunity,and epigenetic analysis,ect.2.Bioinformatics methods were used to analyze the expression,prognosis,and potential molecular mechanism of sirtuins（SIRTs）in gastric cancer.Quantitative real-time polymerase chain reaction（RT-q PCR）was used to verify the expression level of differentially expressed genes in the Cancer Genome Altas（TCGA）between gastric cancer and paracancerous tissue samples,as well as gastric cancer cell lines and normal epithelial cells of gastric mucosa.Results:1.We observed that CSMD2 was upregulated in most tumors and had moderate to high diagnostic efficiency,and that high expression was closely associated with poor prognosis in patients with tumors.Moreover,hypermethylation of CSMD2 promoter and high levels of m6A methylation regulators were also observed in most tumors.CSMD2 expression was negatively correlated with tumor mutational burden（TMB）and microsatellite instability（MSI）in stomach adenocarcinoma（STAD）and stomach and esophageal carcinoma（STES）,as well as with TMB,MSI,and tumor neoantigen burden（TNB）in head-neck squamous cell carcinoma（HNSC）.CSMD2 might be associated with immune evasion or immunosuppression in most cancers,as deficient anti-tumor immunity and upregulation of immune checkpoints were also observed in most tumors.Therefore,CSMD2 might be associated with immune evasion or immunosuppression.2.We found that SIRT1 m RNA expression was different in various tumors and SIRT1 protein expressed differently in different tumors.The expression of SIRT1 was negatively correlated with pathological stage in kidney renal clear cell carcinoma（KIRC）（P<0.001）and ovarian cancer（OV）（P<0.01）.Patients with high SIRT1expression had good prognoses in KIRC and brain cancer.SIRT1（NP＿036370.2,S47）was highly expressed in breast cancer(P=1.22×10^-7),colon cancer(P=4.02×10^-9),lung adenocarcinoma（LUAD）(P=5.92×10^-14)and uterine corpus endometrial carcinoma（UCEC）(P=6.68×10^-4)but lowly expressed in ovarian cancer(P=1.58×10^-2)and KIRC(P=3.45×10^-11)by the phosphorylation level of SIRT1 protein analysis.SIRT1（NP＿036370.2,T719）was expressed highly in breast cancer(P=4.56×10^-4)but lowly in UCEC(P=5.66×10^-8).SIRT1 was significantly correlated with cancer-associated fibroblasts（CAFs）in most cancers and negatively correlated with CAFs in testicular germ cell tumors（TGCT）and brain cancer.SIRT1 was also correlated with multiple immune cells infiltration and immune-related molecules,including immune checkpoints,MHC molecules,immunostimulators,ect.SIRT1 expression was positively correlated with TMB and MSI in GBM.In summary,SIRT1 might play an anti-tumor role in KIRC and brain cancer and might serve as an immune biomarker in pan-cancer.Gene Ontology（GO）enrichment analysis found SIRT1 might be related to the rhythm process and transcription.Kyoto Encyclopedia of Genes and Genomes（KEGG）analysis found that the longevity regulation pathway,Fox O signaling pathway,and insulin resistance might be involved in tumorigenesis and development.3.The pan-cancer analysis of SIRT1 indicated that SIRT1 was a meaningful biomarker in multiple tumors,considering the nicotinamide adenine dinucleotide（NAD）as the active center of SIRTs,thus,we study the role of SIRTs in gastric cancer.SIRT1was lowly expressed in gastric cancer cell lines and gastric cancer tissues.Patients with high SIRT1 expression had a good prognosis.SIRT1 had a strong correlation with CNV and methylation.SIRT1 was also positively correlated with some anti-tumor immune cells in gastric cancer.SIRT1,SIRT3,and SIRT5 had strong correlations.There was a strong correlation between SIRT6 and SIRT7.SIRT5,SIRT6,and SIRT7 were highly expressed in gastric cancer.Patients with high SIRT5 expression had good prognoses,whereas,those with high SIRT6 and SIRT7 expression had poor prognoses.SIRT3（AUC=0.733）,SIRT5（AUC=0.800）,and SIRT6（AUC=0.767）also had relatively good diagnostic values.SIRT6 and SIRT7 had strong positive correlations with LGALS9,TMB,and MSI.In addition,we also found that SIRT7 was negatively correlated with most anti-tumor cells and positively correlated with some immune evasion-associated cells.SIRT7 was also positively correlated with methylation.Functional enrichment found that SIRTs might be involved in viral carcinogenesis,nicotinic acid,and nicotinamide metabolism,thyroid hormone signaling pathway,dysregulation of transcription in cancer,longevity regulation pathway,alcoholism,cellular senescence,Fox O signaling pathway,AMPK signaling pathway,cell cycle,Notch signaling pathway,etc.Conclusion:1.CSMD2 could serve as a promising prognostic and diagnostic biomarker,and also a biomarker related to immune escape or immunosuppression in pan-cancer.2.SIRT1 might be a prognostic and immune biomarker in pan-cancer.SIRT1might play different roles as an oncogene or tumor suppressor gene in different tumors.3.SIRT1 might be a promising prognostic biomarker for gastric cancer and a biomarker related to anti-tumor immunity,which also might play a role in the treatment of gastric cancer.SIRT7 might be an oncogene for gastric cancer and serve as a biomarker correlated with immunosuppression or immunotherapy.