title: Tiam1 regulates cell adhesion, migration and apoptosis in colon tumor cells.
abstract: The guanine nucleotide exchange factor Tiam1 regulates numerous biologic properties including migration and invasion. We demonstrated previously that colon tumor cells biologically selected for increased migration were increased in Tiam1 expression. Cells selected for increased Tiam1 expression or that ectopically overexpress Tiam1 were increased in metastatic potential. Here, we demonstrate that Tiam1 regulates additional functions associated with metastasis, including reduced cellular adhesion and resistance to anoikis. Tiam1 effects on cellular migration are mediated through its downstream substrate, Rac. Increased Tiam1 expression also leads to anoikis-resistance, whereas decreasing Tiam1 expression by siRNA sensitizes cells to this form of apoptosis; however, Tiam1's regulation of anoikis is Rac-independent. Staurosporine sensitivity is also Rac-independent, suggesting Tiam1's effects on apoptosis require other effectors. As many of the observed phenotypes are characteristic of a transition of transformed epithelial cells to a mesenchymal-like phenotype, we also examined biochemical properties associated with an EMT. We demonstrate an increase in vimentin expression in cell lines that overexpress Tiam1 and have a more metastatic phenotype. Concomitant with this increase, we observe a decrease in E-cadherin expression in these cells. Lastly, we stained a panel of human colorectal specimens and adjacent normal tissue, and demonstrate that Tiam1 is overexpressed in a subset of human colorectal tumors. In summary, in colon tumor cells, Tiam1 affects multiple properties associated with acquisition of the metastatic phenotype, and may represent a marker of colon tumor progression and metastasis in a subset of tumors.
authors.affiliation: Department of Cancer Biology, The University of Texas MD Anderson Cancer Center, 1515 Holcombe Blvd, Box 173, Houston, TX 77030, USA.
authors.forename: Meghan E
authors.initials: ME
authors.lastname: Minard
authors.forename: Lee M
authors.initials: LM
authors.lastname: Ellis
authors.forename: Gary E
authors.initials: GE
authors.lastname: Gallick
mesh_terms: D000230:Adenocarcinoma / Q000378:metabolism / Q000473:pathology*; D000368:Aged; D023102:Anoikis / Q000502:physiology; D017209:Apoptosis / Q000502:physiology; D002448:Cell Adhesion / Q000502:physiology; D045744:Cell Line, Tumor / Q000378:metabolism / Q000473:pathology; D002465:Cell Movement / Q000502:physiology; D003110:Colonic Neoplasms / Q000378:metabolism / Q000473:pathology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D020662:Guanine Nucleotide Exchange Factors / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008297:Male; D008648:Mesoderm; D008875:Middle Aged; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D010641:Phenotype; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D011993:Recombinant Fusion Proteins; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D014162:Transfection; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000502:physiology
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D009363:Neoplasm Proteins; C107953:RAC1 protein, human; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C087334:TIAM1 protein, human; D020830:rac1 GTP-Binding Protein