Proto-oncogene CT45A1 Acts As An Activator Of Gene Transcription To Promote Lung Cancer Growth And Metastasis

Lung cancer has become one of the most malignant tumors to threat the health and life of human beings. The incidence of the disease comes to be higher and higher, and the 5-year survival rate for the lung cancer patients is just 16%. Metastasis(mainly in brain and bone) is the principle death causal of lung cancer. In recent years, the numerous studies have revealed that lung cancer is a malignant tumor with abnormality of multiple genes, and that the aberrant activation of oncogenes, the inactivation of tumor suppressor genes, and the overexpression of multiple proto-oncogenes, play an important role in the initiation and metastasis of lung cancer. However, why so many oncogenes are aberrantly overexpressed in lung cancer? How to effectively inhibit the overexpressed oncogenes in the patients with lung cancer has become a key scientific problem to be solved.We have recently studied the mechanisms of oncogene overexpression in lung cancer. Although people have extensively studied intracellular universal gene transcriptional complex(transcriptional machinery) which mainly consists of the promoter, transcription factor, transcriptional activator, and RNA polymerase II(Pol II), the mechanism of abnormal activation of the transcriptional machinery and production of multiple oncogenes in lung cancer is still enigmatic. Recently, we found that CT45A1 could induce overexpression of more than 500 genes, promote EMT and malignant evolution of low tumorigenic breast cancer cells, enhance cell stemness, resulting in breast cancer invasion and lung metastasis; accordingly, we raised a new concept that CT45A1 acts as a new proto-oncogene to promote the evolution and metastasis of the tumor cells, but its mechanism is unclear.According to our preliminary research results,we propose the following scientific hypothesis: After overexpression of CT45A1 in lung cancer cells by endorgenous and exdorgenous factors, CT45A1 activates the gene transcriptional machinery, causes overexpression of various lung cancer-related genes, resulting in lung cancer progression and metastasis. Focusing on the scientific hypothesis, we carried out a series of studies at the four levels of molecular biology, cell biology, aminals in vivo, and clinical lung cancer patients.First of all, we revealed that CT45A1 gene promoter was activated in lung cancer cells, the activation of CT45A1 gene was closely related to the demethylation of the promoter region of the gene, and that the transcription factor SP1 bound to the SP1 binding site at the near distance promoter region of CT45A1 gene to drive the transcription of the gene.Next, we utilized bioinformatic analysis to reveal that CT45A1 protein contains two cell nuclear localization signal peptides(NLS), and there is a DEAD/ H domain at the C-terminus of the protein, which can interact with RNA polymerase II(pol II), suggesting that CT45A1 may play a role in cell nuclear function. We experimentally confirmed that CT45A1 distributed at the nucleus in lung cancer cells.Following, we used dual luciferase reporter gene system, RT-PCR, immunoblotting to confirm that CT45A1 promoted C-kit gene overexpression. In addition, immunoprecipitation showed that CT45A1 could interact with pol II、SP1 and other key proteins in gene transcriptional machinery, implying that CT45A1 can act as a new gene transcriptional activator.Furthermore, we used mouse subcutaneous xenograft and in suit lung cancer model to verifiy the role of CT45A1 in lung cancer development. Mouse subcutaneous xenograft model showed that the tumor weight in the CT45A1 group was 10.2 times more than that of the control, indicating that CT45A1 can significantly promote tumor growth. The in suit lung cancer model also displayed that CT45A1 could boost the growth, invasion, and brain metastasis of lung cancer. Molecular mechanistic analysis showed CT45A1 escalated overexpression of stem cell gene C-kit, key metastastic gene CXCR4, and lung cancer marker CEA. Also, we found that CT45A1 constutitively enhanced phosphorylation of STAT3 and activated JAK-STAT signaling pathway. Collectively,these results suggest that CT45A1 can enhance the tumorigenicity of lung cancer, promote the growth, invasion, and metastasis of lung cancer.In light of that the relationship between CT45A1 overexpression and the prognosis of cancer patients has no been reported in the literature, we collected and analyzeed the lung tissues from 284 lung cancer patients and 30 cases of pneumonia tissues after surgery to analyze the relationship between CT45A1 expression levels and the prognosis of the lung cancer patients. The results showed that CT45A1 was not expressed in the pneumonia tissues, but overexpressed in 187 lung cancer tissues; the positive rate was as high as 65.8%, which is higher than most other lung cancer markers reported in the literature. More interestingly, we also found overexpression of CT45A1 is closely related to the poor prognosis of the lung cancer patients.In summary, we found that CT45A1 acts as a transcriptional activator to promote overexpression of various oncogenes in lung cancer, to boost lung cancer growth, invasion, metastasis, providing new strategies and molecular targets for the diagnosis and treatment of lung cancer.