Proteomic and Interactome Approaches Reveal PAK4, PHB-2, and 14-3-3η as Targets of Overactivated Cdc42 in Cellular Responses to Genomic Instability.

Cdc42, a member of the Rho GTPase family, is an intracellular signaling protein known for its roles in cytoskeleton rearrangements and, more recently, in apoptosis/senescence triggered by genotoxic stress. In some tumor cells, the overactivation of Cdc42 through the expression of constitutively active mutants (G12V or Q61L), GEF activation, or GAP downregulation functions as an antiproliferative or pro-aging mechanism. In this study, human cell lines with different P53 protein profiles were exposed to UV radiation, and the interactions between Cdc42 and proteins that are putatively involved in the DNA damage response and repair mechanisms were screened. The affinity-purified proteins obtained through pull-down experiments of the cell lysates using the recombinant protein baits GST, GST-Cdc42-WT, or GST-Cdc42-G12V were identified by mass spectrometry. The resulting data were filtered and used for the construction of protein-protein interaction networks. Among several promising proteins, three targets, namely, PAK4, PHB-2, and 14-3-3η, which are involved in the cell cycle, apoptosis, DNA repair, and chromatin remodeling processes, were identified. Biochemical validation experiments showed physical and proximal interactions between Cdc42 and the three targets in the cells, particularly after exposure to UV. The results suggest that the molecular mechanisms coordinated by overactivated Cdc42 (with the G12V mutation) to increase the cellular sensitivity to UV radiation and the susceptibility to cell death are collectively mediated by these three proteins. Therefore, the Cdc42 GTPase can potentially be considered another player involved in maintenance of the genomic stability of human cells during exposure to genotoxic stress.

Proteomic and interactome approaches reveal PAK4, PHB-2, and 14-3-3n as targets of overactivated Cdc42 in cellular responses to genomic instability

Cdc42, a member of the Rho GTPase family, is an intracellular signaling protein known for its roles in cytoskeleton rearrangements and, more recently, in apoptosis/senescence triggered by genotoxic stress. In some tumor cells, the overactivation of Cdc42 through the expression of constitutively active mutants (G12V or Q61L), GEF activation, or GAP downregulation functions as an antiproliferative or pro-aging mechanism. In this study, human cell lines with different P53 protein profiles were exposed to UV radiation, and the interactions between Cdc42 and proteins that are putatively involved in the DNA damage response and repair mechanisms were screened. The affinity-purified proteins obtained through pull-down experiments of the cell lysates using the recombinant protein baits GST, GST-Cdc42-WT, or GST-Cdc42-G12V were identified by mass spectrometry. The resulting data were filtered and used for the construction of protein–protein interaction networks. Among several promising proteins, three targets, namely, PAK4, PHB-2, and 14-3-3?, which are involved in the cell cycle, apoptosis, DNA repair, and chromatin remodeling processes, were identified. Biochemical validation experiments showed physical and proximal interactions between Cdc42 and the three targets in the cells, particularly after exposure to UV. The results suggest that the molecular mechanisms coordinated by overactivated Cdc42 (with the G12V mutation) to increase the cellular sensitivity to UV radiation and the susceptibility to cell death are collectively mediated by these three proteins. Therefore, the Cdc42 GTPase can potentially be considered another player involved in maintenance of the genomic stability of human cells during exposure to genotoxic stress.

Proteomic and interactome approaches reveal PAK4, PHB-2, and 14-3-3n as targets of overactivated Cdc42 in cellular responses to genomic instability

Cdc42, a member of the Rho GTPase family, is an intracellular signaling protein known for its roles in cytoskeleton rearrangements and, more recently, in apoptosis/senescence triggered by genotoxic stress. In some tumor cells, the overactivation of Cdc42 through the expression of constitutively active mutants (G12V or Q61L), GEF activation, or GAP downregulation functions as an antiproliferative or pro-aging mechanism. In this study, human cell lines with different P53 protein profiles were exposed to UV radiation, and the interactions between Cdc42 and proteins that are putatively involved in the DNA damage response and repair mechanisms were screened. The affinity-purified proteins obtained through pull-down experiments of the cell lysates using the recombinant protein baits GST, GST-Cdc42-WT, or GST-Cdc42-G12V were identified by mass spectrometry. The resulting data were filtered and used for the construction of protein–protein interaction networks. Among several promising proteins, three targets, namely, PAK4, PHB-2, and 14-3-3?, which are involved in the cell cycle, apoptosis, DNA repair, and chromatin remodeling processes, were identified. Biochemical validation experiments showed physical and proximal interactions between Cdc42 and the three targets in the cells, particularly after exposure to UV. The results suggest that the molecular mechanisms coordinated by overactivated Cdc42 (with the G12V mutation) to increase the cellular sensitivity to UV radiation and the susceptibility to cell death are collectively mediated by these three proteins. Therefore, the Cdc42 GTPase can potentially be considered another player involved in maintenance of the genomic stability of human cells during exposure to genotoxic stress.

Measuring the Contributions of the Rho Pathway to the DNA Damage Response in Tumor Epithelial Cells.

Actin polymerization, actomyosin ring contraction, and stress fiber formation are examples of relevant actions of the RhoA/B/C pathway as GTPases that regulate the cytoskeleton. However, open questions that remain to be addressed are whether this pathway and/or downstream components protect against or facilitate the formation of DNA double-strand breaks, the most lethal form of DNA damage in cells. Genotoxic drugs are radiomimetic and/or chemotherapeutic agents that are currently used for cancer treatments and are associated with specific methodologies; thus, these compounds should represent good tools to answer these questions. In this chapter, we describe two methods, the alkaline comet assay and homologous/nonhomologous recombination assays, to investigate the mechanism by which the Rho pathway modulates the repair of DNA breaks in tumor epithelial cell lines.