| Widespread metastasis is a common phenomenon and the major lethal cause of cancer. So far, however, very little is known about the mechanisms underlying metastasis. Once the key factors in tumor metastasis were identified, the drug targets and diagnosis markers could be obtained accordingly.It has been widely reported that many molecules were involved in the complex processes of tumor invasion and metastasis:1) E-cadherin, immunoglobin superfamily, selectin and integrin have been suggested to take part in the detachment of tumor cells from the primary site and interaction of tumor cells with the surrounding extracellular matrix； 2) Matrix-degrading enzymes and their inhibitors secreted by tumor cells ormesenchymal cells have been indicated to be involved in degradation of extracellular matrix and vascular basement; 3) Some growth factors and movememt factors, such as HGF,EGF,AMF,TGF,IFN-γ,IL-1,3,6 and CD44, have been implicated to play role in migration of tumor cells into secondary sites; 4) Angiogenetic factors, such as VEGF, bFGF, IL-8 and PDGF, have been demonstrated to be important in neoangiogenesis and distant metastasis. At present, most of the research associated with metastasis so far has been focused on the genetic changes of related molecules or single or few proteins without systematic study. But little is known about the key factors to trigger tumorigenic cells to initiate further invasion and metastasis facing with so many regulators up to now.On the basis of these considerations, proteomic strategy, combinedwith two-dimensional electrophoresis (2-DE) separation and mass spectrometry (MS) identification with advantage of high resolution, high reproducibility was used to separate and identify differentially expressed proteins between highly and lowly metastatic subpopulations. In this study we hoped to find out a series of protein cluster deeply involved in metastasis process and addressed the question whether there were new proteins to be associated with metastasis, moreover, to clarify themetastasis-associated function mediated by new candidate proteins. In the present study, 11 metastasis-associated proteins were seperated and identified by comparativeproteome technique using established metastatic model, more importantly, the metastasis-associated function mediated by IL-18 was further characterized.1 Characterization of PLA801C and PLA801D subpopulations with different potency of invasion and metastasis in vitroCell motility and invasion assay in vitro using transwell-chamber system demonstrated the significantly different potential of invasion between PLA801C and PLA801D, i.e. the invasion ability of highly metastatic PLA801D was about 4-fold of PLA801C, in addition, the motility potency was similar between PLA801C and PLA801D. Then, MMP and TIMP important in extracellular matrix degradation, and biomarkers associated cell growth, migration, invasion, angiogenesis and metastasis were all employed to explore the molecules associated with the significant difference of the metastatic potentials between PLA801C and PLA801D. Compared with PLA801C, highly metastatic PLA801D with significantly higher invasion and metastatic ability displayed MMP-2 activity to about 1.6 fold, due to the significant up-regulation of its proteinand mRNA. Moreover, the protein level of tumor suppressor protein P53, proliferating cell nuclear antigen PCNA, intermediate filament cytokeratin 18 (CK18) and VEGF mRNA were much higher, while tumor suppressor protein P16, intercellular adhesion molecule E-cadherin and tumor metastasis suppressor protein nm23-H1 were significantly lower in highly metastatic PLA801D compared with lowly metastatic PLA801C, while the expression level of CD44 varient V6, MMP-9, TIMP-1 and TIMP-2 were close between PLA801C and PLA801D, implicating that these factors seemed not associated with metastasis of lung giant cell carcinoma. Obviously, the metastatic phenotype differences between PLA801C and PLA801D were caused by the di...
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