Studies On The Functions Of UCHL1 And NAIF1 In Gastric Cancer Progression

As the common digestive system neoplasm, gastric cancer has threatened human health and the quality of life. According to the global cancer statistic data of 2012, the incidence and mortality of gastric cancer rank the fifth and the third in all human cancers, respectively. Because of the symptom dormant during the early stages of gastric cancer, most patients have already been in advanced stage when they were first diagnosed with distant metastasis, which is the main factor for high lethality rate. Therefore, it is meaningful to find genes related to tumorigenesis, invasion and metastasis in gastric cancer. It will facilitate elucidating the mechanisms of gastric cancer tumorigenesis and progression, as well as identifying new diagnostic markers and therapeutic targets to improve the survival rates.UCHL1 (ubiquitin C-terminal hydrolase-L1) is a member of the de-ubiquitinating enzyme family. It participates in ubiquitin-dependent proteolysis processes in cytoplasm, and is related to the degration of intracellular proteins. The enzymatic activity closely relies on the cysteine at position 90, when mutated to serine, the de-ubiquitinase activity is declined by 107. Therefore, the single mutation is able to abolish UCHL1’s enzymatic activity. In this study, by using immunohistochemistry assay, we found that the positive expression rates of UCHL1 in cancer distal and adjacent gastric mucosa tissues, primary gastric cancer and liver metastasis lesions of gastric cancer were 56.5%,13% and 70%, respectively. The χ2 test with Bonferroni correction indicated a statistically significant difference of UCHL1 expression in primary gastric cancer versus cancer distal and adjacent gastric mucosa tissues (P= 0.002), and in liver metastasis lesions of gastric cancer compared with primary gastric cancer (P= 0.002). Then we employed gastric cancer cell lines BGC823 as well as MKN45 and took advantage of lentiviral transfection system to generate six stable cell lines, which expressed UCHL1 WT, the mutant C90S and empty vector, respectively. Both UCHL1 WT and C90S were located in cytoplasm. Overexpression of UCHL1 promoted cell proliferation, colony formation, migration and invasion depending on its de-ubiquitinase activity. Meanwhile, increased UCHL1 activated Akt and Erkl/2, which also required enzymatic activity and was necessary for UCHL1-mediated enhancement of cell migration and invasion. According to previous studies and our results, we illustrated the unique expression pattern of UCHL1 in gastric related tissues, and that UCHL1 promoted gastric cancer metastasis through above-mentioned machanisms. UCHL1 could become a novel diagnostic marker and a therapeutic target for gastric cancer metastasis.NAIF1 (Nuclear apoptosis-inducing factor 1), also named as C9orf90, could induce apoptosis. Previously, immunohistochemical study has revealed that the expression of NAIF 1 protein is down-regulated in gastric cancer tissues compared with the adjacent normal tissues, and the expression is up-regulated in well-differentiated gastric cancer tissues compared with those moderately or poorly differentiated. It indicates that NAIF1 may exert inhibitory functions during gastric cancer tumorgenesis and progression. However, further study is required to illuminate the relative molecular mechanisms. Our study revealed that in gastric cancer cell lines BGC823 and MKN45, over-expressed NAIF1 down-regulated Erkl/2 both in mRNA and protein levels, leading to lower expression of p-Erkl/2; on the other hand, NAIF1 inhibited the expression of JNK (c-Jun N-terminal kinase) by accelerating its degradation through ubiquitin-proteasome pathway, followed by decreased expression of p-JNK. Through the two MAPK pathways, NAIF1 decreased cell proliferation, migration and invasion in vitro, and inhibited the tumor formation by MKN45 in nude mice. As NAIF1 suppresses malignant phenotype and negatively regulates Erkl/2 and JNK pathways in gastric cancer cells, it has the potential of becoming a molecular marker for gastric cancer diagnoses and a therapeutic target for treatment aimed at MAPK pathways.In this study, we disclose the functions and molecular mechanisms of UCHL1 and NAIF1 in gastric cancer, and provide insights into finding new diagnostic and therapeutic targets for gastric cancer.