LncRNA-CTD suppresses metastasis and immune evasion by modulating snail1 and MHC-I expression in colorectal cancer

Background Distant metastasis and immune evasion are the major obstacles for successful colorectal cancer (CRC) treatment. The link between metastasis and immune evasion, as well as their therapeutic significance, remains unclear. Methods Long non-coding RNAs from six paired CRC and normal tissues were screened by RNA sequencing (RNA-seq). LncRNA-CTD (CTD-2568A17.8) expression levels were determined using in situ hybridization and quantitative PCR analysis. In vitro and in vivo assays were performed to confirm the function of lncRNA-CTD. Flow cytometry was used to analyze the impact of lncRNA-CTD on immune cell infiltration and T-cell function. RNA-seq combined with RNA pull-down and RNA immunoprecipitation assay was used to identify the changes in downstream molecules induced by lncRNA-CTD. The therapeutic value of the combination of lncRNA-CTD and immune checkpoint inhibitors has been evaluated. Results In this study, we identified a novel long non-coding RNA, lncRNA-CTD, which is downregulated in CRC and correlates with both metastasis and immunotherapy response. Mechanistically, the interaction of lncRNA and smad2 prevented the phosphorylation and nuclear translocation of smad2, which inhibited the expression of snail1, thereby inhibiting the metastasis of CRC. LncRNA-CTD enhances major histocompatibility complex class I (MHC-I) expression on the cancer cell membrane by interacting with STUB1 to disrupt the interaction of STUB1 with the MHC-I activator NLRC5 and subsequent NLRC5 ubiquitination-mediated degradation, increasing the susceptibility of CRC cells to being killed by CD8 + T cells. TFAP4 overexpression in CRC cells caused lncRNA-CTD downregulation. Moreover, the combination of lncRNA-CTD gene delivery therapy with immune checkpoint inhibitors exerted an additive effect on tumor growth inhibition. Conclusions Collectively, our study reveals the role and mechanism of lncRNA-CTD in CRC metastasis and immune evasion. Overexpression of lncRNA-CTD suppresses CRC metastasis and improves the efficacy of immune checkpoint inhibitors. Cite Now