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The GTPase and Rho GAP domains of p190, a tumor suppressor protein that binds the M(r) 120,000 Ras GAP, independently
D Z Wang1, M S Nur-E-Kamal, A Tikoo
1Ludwig Institute for Cancer Research, PO Royal Melbourne Hospital, Victoria, Australia.
Abstract:
p190 is a Tyr-phosphorylatable G protein of M(r) 190,000 that binds NH2-terminal SH2 domains of GAP1, a Ras GAP of M(r) 120,000. p190 contains at least two functional domains: a GTPase domain at the NH2 terminus and a GAP domain at the COOH terminus that can attenuate signal-transducing activity of three distinct G proteins (Rac, Rho, and CDC42). Here, we demonstrate that overexpression of either an antisense p190 RNA or a dominant negative mutant (Asn36) of p190 GTPase domain (residues 1-251) but not the wild-type p190 GTPase domain is able to transform normal NIH/3T3 fibroblasts. Furthermore, overexpression of either the wild-type p190 GTPase domain or the COOH-terminal GAP domain can suppress v-Ha-Ras-induced malignant transformation. These results indicate that p190 contains at least two distinct anti-Ras tumor suppressor domains, the GTPase and GAP domains, and suggest that one of the mechanisms underlying the suppression of Ras-transformation by p190 is the attenuation by p190 GAP domain of Rac/Rho/CDC42 signalings, which are essential for Ras-transformation. In fact, the p190 GAP domain alone suppresses the expression of the c-Fos gene, which is mediated by Rac/Rho/CDC42 and is required for oncogenicity of Ras.
Insights
p190 protein has two tumor suppressor domains that inhibit Ras-induced cell transformation. Its GTPase and GAP domains block Rac/Rho/CDC42 signaling, suppressing malignant cell growth.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- p190 is a large G protein involved in cell signaling.
- Ras GTPases are key regulators of cell growth and transformation.
- Dysregulation of Ras signaling pathways is implicated in cancer development.
Purpose of the Study:
- To investigate the role of p190 protein domains in Ras-mediated cell transformation.
- To identify functional domains of p190 that exhibit tumor suppressor activity.
- To elucidate the molecular mechanisms by which p190 inhibits Ras oncogenicity.
Main Methods:
- Overexpression of antisense p190 RNA and dominant-negative p190 mutants in NIH/3T3 fibroblasts.
- Analysis of NIH/3T3 fibroblast transformation induced by v-Ha-Ras.
- Assessment of GTPase and GAP domain functions in suppressing malignant transformation.
- Investigation of c-Fos gene expression regulation by p190.
Main Results:
- Overexpression of antisense p190 RNA or a dominant-negative p190 GTPase mutant induced fibroblast transformation.
- Wild-type p190 GTPase domain and the COOH-terminal GAP domain suppressed v-Ha-Ras-induced transformation.
- The p190 GAP domain attenuated Rac/Rho/CDC42 signaling pathways.
- p190 GAP domain suppressed c-Fos gene expression, a key mediator of Ras oncogenicity.
Conclusions:
- p190 possesses distinct GTPase and GAP domains that function as anti-Ras tumor suppressors.
- p190 inhibits Ras-transformation by attenuating Rac/Rho/CDC42 signaling pathways.
- Suppression of c-Fos gene expression is a critical mechanism for p190's anti-Ras activity.