RESUMO
T-cell lymphoma invasion and metastasis-inducing factor 1 (Tiam-1) is an important member of the diffuse B-cell lymphoma (Dbl) oncogene family. In a previous study, the overexpression of Tiam-1 protein was identified by immunohistochemistry in human gastric cancer tissues, indicating that Tiam-1 may represent a candidate biomarker of the invasive and metastatic capacity of gastric cancer and for patient prognosis. In the present study, in vitro adhesion selection was used to separate two subpopulations with high (MH) or low (ML) invasive and metastatic potential from the MKN-45 human gastric cancer cell line (M0). A positive correlation was observed between Tiam-l mRNA and protein expression levels and the invasive capacity of the cells using RT-PCR and quantitative cellular-ELISA, respectively. To determine the mechanism by which Tiam-1 affects the invasive capacities of gastric cancer cells, Tiam-1 expression was downregulated in the MH subclone by liposomal transfection of antisense oligodeoxynucleotides (ASODNs). Following 48 h of treatment with ASODNs (0.43 µM), Tiam-1 mRNA transcription and protein expression levels in MH cells was decreased by 80 and 24%, respectively, compared with untreated controls. In addition, the in vitro invasive potential of MH cells was suppressed by 60%. Morphological and ultrastructural observations also demonstrated that ASODN-treated MH cells exhibited a smooth surface with markedly reduced filopodia and microspikes, which resembled M0 and ML cells. In addition, cytoskeletal distribution was markedly altered from disordered to regular with reduced long filament-like structures, projections, pseudopodia on the cell surface and decreased actin bodies in the cytoplasm. Results of the current study indicate that the overexpression of Tiam-1 contributes to the invasive phenotypes of gastric cancer cells. These observations are likely to provide an improved insight into the biological mechanisms of Tiam-1 and promote the development of novel treatment strategies in gastric cancer.