| Summary: | 碩士 === 國立臺灣大學 === 微生物學研究所 === 90 === Latent membrane protein 2A (LMP2A) is the latent product of Epstein-Barr virus (EBV). Structurally, LMP2A possesses many functional motifs, which potentiate its ability of interacting with cellular signaling molecules. In the light of the previous study in our laboratory that LMP2A can promote the phosphorylation of a 70-kilodalton protein (p70) in epithelial cells and the known fact that LMP2A activates Syk in the lymphoblastoid cell line (LCL), we hypothesized that p70 very likely is the Syk protein with molecular mass 72 kDa. Therefore, the possible mechanisms of LMP2A-mediated regulation of Syk in epithelial cells are the major focus in this study.
In order to investigate the function of LMP2A in epithelial cells, three LMP2A-expressing cell clones (2A-1, 2A-2, 2A-3) and one vector control clone (V) have been established in our lab. Firstly, LMP2A was demonstrated as a highly tyrosine phosphorylated molecule by Western blot analysis. Using deletion and point mutation analysis, it showed that the a.a. 65-112 of LMP2A, with Y74 and Y85 residues in particular, are important for the tyrosine phosphorylation of LMP2A. The results of bi-directional immunoprecipitation and Western blot analysis indicated that the p70 molecule is very likely to be Syk which is tyrosine phosphorylated under influence of LMP2A. In addition, data from serial mutant experiments demonstrated that both Y74 and Y85 residues are necessary for the LMP2A-mediated tyrosine-phosphoarylation of Syk. Furthermore, The main domain required for the interaction with Syk is located at a.a. 65-79.
Taken together, the effects exerted by LMP2A might be different between epithelial cells and B cells. In epithelial cells, the a.a. 65-112, especially Y74 and Y85 residues are important to tyrosine phosphorylation of LMP2A. Also, both Y74 and Y85 are necessary for LMP2A-mediated tyrosine phosphorylation of Syk, however, these two residues are not required for the interaction of LMP2A and Syk. While in B cells, only Y112 is essential for the tyrosine phosphorylation of LMP2A. All Y74, Y85, and Y112 residues are required for the action of LMP2A-triggered tyrosine phosphorylation of Syk; but only Y74 and Y85 residues are crucial for the interaction of LMP2A and Syk. All the data implicated that LMP2A may use a different way in interacting with Syk in epithelial cells than that of in B cells.
To our knowledge, this is the first report that LMP2A can interact with Syk and affect the tyrosine phosphorylation of Syk in epithelical cells. Moreover, the activated Syk may also activate other kinases to promote the metastasis of tumor cells. The role of LMP2A in NPC carcinogenesis would be discussed.
|
|---|
