Roles Of CT55 In Colitis-associated Colorectal Cancer Development

Colorectal cancer(CRC)is one of the most common malignancies with high incidence in the world.The incidence of colorectal cancer in China also shows a rising trend for the past few years.Previous research studies have proven that the pathogenesis of most CRC cases was related to environmental factors,while only 20-30% of cases have a familial basis.CAC is a CRC subtype that often occurs in the context of inflammatory bowel disease and becomes one of the research hotspots in recent years.With the development of studies on cancer testis antigen(CT antigen),it has been found that CT antigen plays an important role in immunotherapy of various tumors including colorectal cancer.As a potential cancer testis antigen,cancer testis antigen 55(CT55)is expressed in colorectal cancer.However,its role in CAC remains unknown.Here,we identified the function and mechanism of CT55 in CAC at the first time.Previous studies have shown that CT antigens can be expressed in a various of tumor tissues.Several members of the CT antigen including MAGE and SSX family have been shown to be expressed in colorectal cancer tissues.In this study,we detected mRNA level of CT55 in 12 paired colon and adjacent nontumor human colon tissues and the results demonstrated that the CT55 was upregulated in 6 out of 12 tumor tissues compared to the paired nontumor tissues.Since CT55 has been reported to be a potential CT antigen,we next examined CT55 expression in various tissues from wild-type(WT)mice and found that CT55 expression was relatively higher in testis and lower in colorectum.Then,we explored the influence of CT55 on the development of CAC.Ct55 knockout mice were generated by CRISPR/Cas9-mediated genome editing and used for AOM/DSS induced colitis-associated colorectal tumorigenesis model.During the generation of the AOM/DSS model,the Ct55 knockout mice exhibited less weight loss than the WT mice;Moreover,the number of macroscopically visible tumors was significantly decreased in the Ct55 knockout mice,and the tumors in the Ct55 knockout mice were markedly smaller in size compared with those in the WT mice.And the further researches have shown that Ct55 deficiency alleviates the inflammatory response and inhibits cell proliferation during colitis-associated colorectal tumorigenesis.We then explored the effect of CT55 on tumorigenic features and the results showed that CT55 deficiency inhibits the tumorigenic features of colorectal cancer cells.Mechanistically,we found CT55 acts as an accelerator of tumor necrosis factor(TNF)-?-induced nuclear factor-?B(NF-?B)signaling by RNA-seq analysis.Specifically,we found CT55 can interacts with the I?B kinase(IKK)complex,which increases the phosphorylation of IKK?/?,then,I?B kinase is phosphorylated by the IKK complex,and is targeted for ubiquitination-and proteosome-dependent degradation.Then,NF-?B is released and translocated into the nucleus,triggering the transcription of downstream genes.Notably,inhibition of IKK by IKK inhibitor abolished the positive effect of CT55 on NF-?B activation.Collectively,our findings strongly indicate that CT55 deficiency suppresses the development of CAC and that the CT55-TNF-?-induced NF-?B axis may represent a promising target for CAC therapy.