title: Cooperative role of caveolin-1 and C-terminal Src kinase binding protein in C-terminal Src kinase-mediated negative regulation of c-Src.
abstract: In the present study, we assessed the cooperative roles of C-terminal Src kinase (Csk) binding protein (Cbp) and Caveolin-1 (Cav-1) in the mechanism of Src family tyrosine kinase (SFK) inhibition by Csk. SFKs are inactivated by phosphorylation of their C-terminal tyrosine by Csk. Whereas SFKs are membrane-associated, Csk is a cytoplasmic protein and therefore requires membrane adaptors such as Cbp or Cav-1 for recruitment to the plasma membrane to mediate SFK inhibition. To determine the specific role of Cav-1 and Cbp in SFK inhibition, we measured c-Src activity in the absence of each membrane adaptor. It is noteworthy that in lungs and fibroblasts from Cav-1(-/-) mice, we observed increased expression of Cbp compared with wild-type (WT) controls. However, both c-Src activity and Csk localization at the membrane were similar between Cav-1(-/-) fibroblasts and WT cells. Likewise, Cbp depletion by small interfering RNA (siRNA) treatment of WT cells had no effect on basal c-Src activity, but it increased the phosphorylation state of Cav-1. Immunoprecipitation then confirmed increased association of Csk with phosphomimicking Cav-1. Knockdown of Cbp by siRNA in Cav-1(-/-) cells revealed increased basal c-Src activity, and re-expression of WT Cav-1 in the same cells reduced basal c-Src activity. Taken together, these results indicate that Cav-1 and Cbp cooperatively regulate c-Src activity by recruiting Csk to the membrane where it phosphorylates c-Src inhibitory tyrosine 529. Furthermore, when either Cav-1 or Cbp expression is reduced or absent, there is a compensatory increase in the phosphorylation state or expression level of the other membrane-associated Csk adaptor to maintain SFK inhibition.
authors.affiliation: Department of Pharmacology, University of Illinois at Chicago, Chicago, IL 60612, USA.
authors.forename: Aaron T
authors.initials: AT
authors.lastname: Place
authors.forename: Zhenlong
authors.initials: Z
authors.lastname: Chen
authors.forename: Farnaz R
authors.initials: FR
authors.lastname: Bakhshi
authors.forename: Guoquan
authors.initials: G
authors.lastname: Liu
authors.forename: John P
authors.initials: JP
authors.lastname: O'Bryan
authors.forename: Richard D
authors.initials: RD
authors.lastname: Minshall
mesh_terms: D000818:Animals; D000081247:CSK Tyrosine-Protein Kinase; D002352:Carrier Proteins / Q000502:physiology*; D051242:Caveolin 1 / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D002478:Cells, Cultured; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010766:Phosphorylation / Q000502:physiology; D011485:Protein Binding / Q000502:physiology; D011505:Protein-Tyrosine Kinases / Q000502:physiology*; D018909:src Homology Domains / Q000502:physiology*; D019061:src-Family Kinases
chemical_list: D002352:Carrier Proteins; D051242:Caveolin 1; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases