Abstract
The Rho GDP dissociation inhibitor D4-GDI is overexpressed in some human breast cancer cell lines (Zhang, Y., and Zhang, B. (2006) Cancer Res. 66, 5592-5598). Here, we show that silencing of D4-GDI by RNA interference abrogates tumor growth and lung metastasis of otherwise highly invasive MDA-MB-231 breast cancer cells. Under anchorage-independent culture conditions, D4-GDI-depleted cells undergo rapid apoptosis (anoikis), which is known to hinder metastasis. We also found that D4-GDI associates with Rac1 and Rac3 in breast cancer cells, but not with other Rho GTPases tested (Cdc42, RhoA, RhoC, and TC10). Silencing of D4-GDI results in constitutive Rac1 activation and translocation from the cytosol to cellular membrane compartments and in sustained activation of p38 and JNK kinases. Rac1 blockade inhibits p38/JNK kinase activities and the spontaneous anoikis of D4-GDI knockdown cells. These results suggest that D4-GDI regulates cell function by interacting primarily with Rac GTPases and may play an integral role in breast cancer tumorigenesis. D4-GDI could prove to be a potential new target for therapeutic intervention.
MeSH terms
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Animals
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Anoikis
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Apoptosis
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Blotting, Western
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Breast Neoplasms / metabolism*
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Breast Neoplasms / pathology
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Breast Neoplasms / prevention & control
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Cell Adhesion
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Cell Line, Tumor
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Cell Movement
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Cell Proliferation
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Female
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Gene Silencing / physiology*
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Guanine Nucleotide Dissociation Inhibitors / genetics*
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Humans
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Immunoprecipitation
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JNK Mitogen-Activated Protein Kinases / metabolism*
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Lung Neoplasms / metabolism
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Lung Neoplasms / prevention & control
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Lung Neoplasms / secondary
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Mice
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Mice, Nude
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Neoplasm Invasiveness
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RNA, Small Interfering / pharmacology
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Signal Transduction
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Tumor Suppressor Proteins / genetics*
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p38 Mitogen-Activated Protein Kinases / metabolism*
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rac1 GTP-Binding Protein / genetics
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rac1 GTP-Binding Protein / metabolism*
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rho Guanine Nucleotide Dissociation Inhibitor beta
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rho-Specific Guanine Nucleotide Dissociation Inhibitors
Substances
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ARHGDIB protein, human
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Guanine Nucleotide Dissociation Inhibitors
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RAC1 protein, human
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RNA, Small Interfering
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Tumor Suppressor Proteins
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rho Guanine Nucleotide Dissociation Inhibitor beta
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rho-Specific Guanine Nucleotide Dissociation Inhibitors
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JNK Mitogen-Activated Protein Kinases
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p38 Mitogen-Activated Protein Kinases
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rac1 GTP-Binding Protein