title: The rac activator Tiam1 is a Wnt-responsive gene that modifies intestinal tumor development.
abstract: Mutations in the canonical Wnt signaling pathway leading to its activation are known to cause the majority of intestinal tumors. However, few genes targeted by this pathway have been demonstrated to affect tumor development in vivo. Here we show that Tiam1, a selective Rac GTPase activator, is a Wnt-responsive gene expressed in the base of intestinal crypts and up-regulated in mouse intestinal tumors and human colon adenomas. Moreover, by comparing tumor development in APC mutant Min (multiple intestinal neoplasia) mice expressing or lacking Tiam1, we found that Tiam1 deficiency significantly reduces the formation and growth of polyps in vivo. However, invasion of malignant intestinal tumors is enhanced by a lack of Tiam1. In line with this, knock-down of Tiam1 reduced the growth potential of human colorectal cancer cells and their ability to form E-cadherin-based adhesions, a prerequisite for local invasion of tumor cells. Our data indicate a novel cross-talk between Tiam1-Rac and canonical Wnt-signaling pathways that influences intestinal tumor formation and progression.
authors.affiliation: Division of Cell Biology, Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.
authors.forename: Angeliki
authors.initials: A
authors.lastname: Malliri
authors.forename: Tomasz P
authors.initials: TP
authors.lastname: Rygiel
authors.forename: Rob A
authors.initials: RA
authors.lastname: van der Kammen
authors.forename: Ji-Ying
authors.initials: JY
authors.lastname: Song
authors.forename: Rainer
authors.initials: R
authors.lastname: Engers
authors.forename: Adam F L
authors.initials: AF
authors.lastname: Hurlstone
authors.forename: Hans
authors.initials: H
authors.lastname: Clevers
authors.forename: John G
authors.initials: JG
authors.lastname: Collard
mesh_terms: D000236:Adenoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D002478:Cells, Cultured; D015179:Colorectal Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D015972:Gene Expression Regulation, Neoplastic; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; D014162:Transfection; D051153:Wnt Proteins / Q000378:metabolism*; D020744:rac GTP-Binding Proteins / Q000378:metabolism
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D009363:Neoplasm Proteins; D000075684:T-Lymphoma Invasion and Metastasis-inducing Protein 1; C513260:Tiam1 protein, mouse; D051153:Wnt Proteins; D020744:rac GTP-Binding Proteins