Molecular Regulation Mechanism Of KRT19 And Construction Of Prognostic Model In Breast Cancer

Objective:Breast cancer is one of the most common malignant tumors among women in most countries in the world.At present,the KRT19 translated protein CYFRA21.1 is mostly used to assist clinical diagnosis and treatment of breast cancer,and its role in immune invasion and prognosis in breast cancer has rarely been studied.Based on this,this study aimed to explore the expression of KRT19 in breast cancer,its prognostic role,epigenetic variation,possible carcinogenic mechanism and its correlation with immune invasion.Methods:1092 breast cancer tissues and 113 normal breast tissues from the TCGA database were included.To improve the reliability of data comparison,we also included 179 normal breast tissues from the GTEx database as a control group to explore the differential expression of KRT19 at the transcriptional level in breast cancers.In addition,to analyze the differential expression of KRT19 on proteins,125 breast cancer tissues and 18 normal breast tissues from the CPTAC database were includedfor the study.And the results were visualized by the UALCAN online tool.To investigate the epigenetic variation of KRT19 in breast cancer,we first searched for its possible genetic alterations through cBioPortal.Secondly,methylation site alterations and differences in protein phosphorylation levels of KRT19 were continued to explore by using the UNCLAN tool.Then,we tused the R package"DESeq2" to screen for differentially expressed genes between patients with high and low KRT19 expression,and performed GO enrichment and KEGG pathway analysis of differentially expressed genes.It was followed by a comprehensive study of the relationship between KRT19 and the immune system in breast cancer via the TISIDB and TIMER databases.Finally,in order to create models that can predict the prognosis of breast cancer patients,we used the "rms" program to create Nomo.Results:KRT19 showed higher expression in breast cancer compared to normal breast tissue.In addition,epigenetic variants of KRT19 displayed diversity in breast cancer.Among them,amplification was the main form of KRT19 gene alteration,accounting for 1.5%,which was higher than missense mutation（0.5%）..Promoter methylation level of KRT19 was significantly down-regulated in breast cancer（P<0.01）.Meanwhile,KRT19 underwent mainly m5C modification,with NSUN5,NSUN4 and TRDMT1 acting as writers to catalyze m5C modification of KRT19.KRT19 phosphorylation occurred at NP₀02267.2 and was upregulated at all loci such as S13.Further analysis of GO enrichment,KEGG pathway and GSEA enrichment indicated that KRT19 may be involved in regulation through signaling pathways such as IL-17 signaling pathway and estrogen response in breast cancer.Subsequently,we focused on analyzing the correlation between KRT19 and tumor immune microenvironment.The results displayed that the expression of KRT19 in breast cancer was negatively correlated with the level of immune infiltration of most immune cells,especially Tcm,Thl cells and T helper cells.In contrast,the level of immune infiltration of NK CD56bright cells,NK cells and mast cells was positively correlated with the expression of KRT19.Moreover,we also found that the expression of KRT19 combined with immune infiltration could observe the prognosis of breast cancer patients.When KRT19 was lowly expressed,Low T-cell CD8+suggested a poor prognosis compared to High T-cell CD8+;however,when KRT19 was highly expressed,Low T-cell CD8+also indicated a poor prognosis.In addition,the prognostic model constructed by the expression level of KRT19 combined with the expression of genes associated with cancer immune cycle characteristics（RAET1G,IL12B,CXCL13 and CCL22）could well predict the prognosis of breast cancer patients with a consistency index of 0.634.Conclusions:1.In breast cancer,KRT19 exhibited high expression at both transcriptional and protein levels.2.In breast cancer,preliminary exploration of the molecular regulatory mechanism of KRT19 suggested that it undergoes epigenetic variation and may affect the development of breast cancer by regulating the IL-17 signaling pathway.3.In breast cancer,the expression of KRT19 was closely related to the level of immune infiltration of immune cells,and the combination of them could effectively assess the prognosis of breast cancer patients.