Tiam1-deficiency impairs mammary tumor formation in MMTV-c-neu but not in MMTV-c-myc mice

J Cancer Res Clin Oncol. 2009 Jan;135(1):69-80. doi: 10.1007/s00432-008-0437-8. Epub 2008 Jul 1.


Background: Rho-like small GTPases, including RhoA, Rac1 and Cdc42, are crucial for the regulation of a large variety of biological processes such as the cytoskeletal organization and gene transcription. The activities of Rho GTPases are predominantly controlled by guanine nucleotide exchange factors (GEFs), which activate GTPases by catalyzing the exchange of bound GDP for GTP. Earlier, we have identified the Tiam1 gene as an invasion-inducing gene that encodes a specific activator (GEF) of the Rac GTPase. We found that Tiam1-mediated Rac signaling functions in various aspects of tumorigenicity including the formation and progression of Ras-induced skin tumors and Wnt-induced intestinal tumors. Here, we further distinguish the oncogenic pathways that depend on Tiam1 signaling in the mammary gland.

Material and methods: We crossed Tiam1 knockout mice with MMTV-c-myc and MMTV-c-neu transgenic mice, in which the expression of both oncogenes is targeted to the mammary gland leading to mammary tumorigenesis.

Results: We found Tiam1 important for Neu-induced tumor formation and progression but not for Myc-induced tumors. Tiam1-deficiency delayed Neu-induced tumor initiation and reduced metastasis but had no effect on the growth of the MMTV-c-neu tumors.

Conclusion: Our data indicate that the Rac activator Tiam1 contributes to tumorigenicity induced by specific oncogenic signaling pathways only.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apoptosis
  • Blotting, Western
  • Cell Differentiation
  • Female
  • Guanine Nucleotide Exchange Factors / physiology*
  • Humans
  • Immunoenzyme Techniques
  • Lung Neoplasms / prevention & control
  • Lung Neoplasms / secondary
  • Male
  • Mammary Glands, Animal / metabolism
  • Mammary Glands, Animal / pathology
  • Mammary Neoplasms, Animal / pathology
  • Mammary Neoplasms, Animal / prevention & control*
  • Mammary Neoplasms, Animal / virology
  • Mammary Tumor Virus, Mouse / genetics*
  • Mice
  • Mice, Knockout
  • Mice, Transgenic
  • Precancerous Conditions / metabolism
  • Precancerous Conditions / pathology
  • Proto-Oncogene Proteins c-myc / physiology*
  • Receptor, ErbB-2 / physiology*
  • Survival Rate
  • T-Lymphoma Invasion and Metastasis-inducing Protein 1


  • Guanine Nucleotide Exchange Factors
  • Myc protein, mouse
  • Proto-Oncogene Proteins c-myc
  • T-Lymphoma Invasion and Metastasis-inducing Protein 1
  • Tiam1 protein, mouse
  • Receptor, ErbB-2