Pan-cancer analysis of LncRNA XIST and its potential mechanisms in human cancers.

Background: X-inactive specific transcript (XIST), it has been found, is abnormal expression in various neoplasms. This work aims to explore its potential molecular mechanisms and prognostic roles in types of malignancies. Methods: This research comprehensively investigated XIST transcription across cancers from Oncomine, TIMER 2.0 and GEPIA2. Correlations of XIST expression with prognosis, miRNAs, interacting protens, immune infiltrates, checkpoint markers, mutations of tumor-associated genes and promoter methylation were also analyzed by public databases. In addition, 98 BRCA samples were collected to investigate XIST expression and evaluate its clinicopathological value. Results: In public databases, compared to normal tissues, XIST was lower in BRCA, CESC, COAD and so on, but increased in KIRC and PRAD. Databases also showed that XIST was a good indicator of prognosis in BRCA, COAD and so on, but a bad one in KIRC, KIRP and so on. From starBase, we found 29 proteins interacting with XIST, and identified 4 miRNAs which might be sponged by XIST in cancers. Furthermore, XIST was linked with immune infiltration, especially T cell CD4+, and was related to over 20 immune checkpoint markers. Moreover, several tumor-associated gene mutations and promoter methylation were negatively related to its expression. In addition, IHC showed that XIST in BRCA was obviously lower in comparison of normal tissues and was negatively related to lymph node invasion and TNM stage. Conclusion: In summary, abnormal expression of XIST influenced prognosis, miRNAs and immune infiltration across cancers, especially BRCA.