Effects of Tiam 1 on Invasive Capacity of Gastric Cancer Cells in vitro and Underlying Mechanisms

Objective: To investigate changes in the invasive capacity of gastric cancer cells in vitro after expressioninhibition of T lymphoma invasion and metastasis inducing factor 1 (Tiam 1) and underlying mechanisms.
Methods: Using adhesion selection, two subpopulations with high (MH) or low (ML) invasive capacity wereseparated from the human gastric cancer cell line MKN-45 (M0). Tiam 1 antisense oligodeoxynucleotide (ASODN)was transfected into MH cells with liposomes, and expression of Tiam 1 mRNA and protein was determined byRT-PCR and quantitative cellular-ELISA. Changes in the cytoskeleton, invasive capacity in vitro and expressionof ras-related C3 botulinum toxin substrate 1 (Rac 1), integrin β1 and matrix metalloproteinase 2 (MMP 2)between Tiam 1 ASODN transfected MH cells and non-transfected cells were observed by HE staining, cytoskeletalprotein staining, scanning electron microscopy, Boyden chamber tests and cyto-immunohistochemistry.
Results:A positive correlation existed between the expression level of Tiam l mRNA or protein and the invasion capacityof gastric cancer cells. After ASODN treatment (0.43 μM for 48 h), Tiam 1 mRNA transcription and proteinexpression in MH cells were decreased by 80% and 24% respectively (P < 0.05), compared with untreated controls,while invasive capacity in vitro was suppressed by 60% (P < 0.05). Morphologic and ultrastructural observationalso showed that ASODN-treated MH cells exhibited smooth surfaces with obviously reduced filopodia andmicrospikes, which resembled M0 and ML cells. Additionally, cytoskeletal distribution dramatically altered fromdisorder to regularity with reduced long filament-like structure, projections, pseudopodia on cell surface, andwith decreased acitn-bodies in cytoplasm. After Tiam 1 ASODN treatment, the expression of Rac 1 and Integrinβ1 in MH cells was not affected (P > 0.05), but that of MMP 2 in MH cells was significantly inhibited comparedwith untreated cells (P < 0.05).
Conclusion: Over-expression of Tiam-1 contributes to the invasive phenotypeof gastric cancer cells. Inhibition of Tiam 1 expression could impair the invasive capacity of gastric cancer cellsthrough modulating reconstruction of the cytoskeleton and regulating expression of MMP 2.