title: Roles of raft-anchored adaptor Cbp/PAG1 in spatial regulation of c-Src kinase.
abstract: The tyrosine kinase c-Src is upregulated in numerous human cancers, implying a role for c-Src in cancer progression. Previously, we have shown that sequestration of activated c-Src into lipid rafts via a transmembrane adaptor, Cbp/PAG1, efficiently suppresses c-Src-induced cell transformation in Csk-deficient cells, suggesting that the transforming activity of c-Src is spatially regulated via Cbp in lipid rafts. To dissect the molecular mechanisms of the Cbp-mediated regulation of c-Src, a combined analysis was performed that included mathematical modeling and in vitro experiments in a c-Src- or Cbp-inducible system. c-Src activity was first determined as a function of c-Src or Cbp levels, using focal adhesion kinase (FAK) as a crucial c-Src substrate. Based on these experimental data, two mathematical models were constructed, the sequestration model and the ternary model. The computational analysis showed that both models supported our proposal that raft localization of Cbp is crucial for the suppression of c-Src function, but the ternary model, which includes a ternary complex consisting of Cbp, c-Src, and FAK, also predicted that c-Src function is dependent on the lipid-raft volume. Experimental analysis revealed that c-Src activity is elevated when lipid rafts are disrupted and the ternary complex forms in non-raft membranes, indicating that the ternary model accurately represents the system. Moreover, the ternary model predicted that, if Cbp enhances the interaction between c-Src and FAK, Cbp could promote c-Src function when lipid rafts are disrupted. These findings underscore the crucial role of lipid rafts in the Cbp-mediated negative regulation of c-Src-transforming activity, and explain the positive role of Cbp in c-Src regulation under particular conditions where lipid rafts are perturbed.
authors.affiliation: Department of Molecular Medicine for Pathogenesis, Graduate School of Medicine, Ehime University, Shitsukawa, Toon, Ehime, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Saitou
authors.affiliation: Department of Oncogene Research, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Kajiwara
authors.affiliation: Department of Oncogene Research, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
authors.forename: Chitose
authors.initials: C
authors.lastname: Oneyama
authors.affiliation: Division of Mathematical Science, Department of Systems Innovation, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka, Japan; JST, CREST, Chiyoda-ku, Tokyo, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Suzuki
authors.affiliation: Department of Oncogene Research, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka, Japan.
authors.forename: Masato
authors.initials: M
authors.lastname: Okada
mesh_terms: D000818:Animals; D000081247:CSK Tyrosine-Protein Kinase; D004622:Embryo, Mammalian; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism*; D051417:Focal Adhesion Kinase 1 / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D005786:Gene Expression Regulation; D007700:Kinetics; D021962:Membrane Microdomains / Q000737:chemistry / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D015233:Models, Statistical; D010750:Phosphoproteins / Q000235:genetics* / Q000378:metabolism; D011485:Protein Binding; D015398:Signal Transduction; D019061:src-Family Kinases / Q000172:deficiency / Q000235:genetics*
chemical_list: D008565:Membrane Proteins; C498709:Pag1 protein, mouse; D010750:Phosphoproteins; D000081247:CSK Tyrosine-Protein Kinase; D051417:Focal Adhesion Kinase 1; C496051:Ptk2 protein, mouse; D019061:src-Family Kinases; C000631346:CSK protein, human