title: Protein kinase activity is associated with CD63 in melanoma cells.
abstract: BACKGROUND
  The tetraspan protein CD63, originally described as a stage-specific melanoma antigen but also present in a number of normal cells, regulates melanoma cell growth in nude mice, motility in serum containing media, and adhesion to several extracellular matrix proteins. CD63 has been reported to associate with beta1 and beta2 integrins, but the mechanism of signal transduction by CD63 is not clear. This study examined whether CD63 is associated with protein kinase and can transmit signals in melanoma cells.
  
  
  METHODS
  Immunoprecipitation and radiolabeling were used to test for association of protein kinase activity with CD63. Adhesion of cells to monoclonal antibodies immobilized to microtiter plates was used to examine the ability of CD63 to transmit signals.
  
  
  RESULTS
  CD63 was capable of transmitting a signal in melanoma cells that required extracellular calcium. In the absence of extracellular calcium at the time of binding to the CD63 mAb, the cell was no longer responsive to stimulation by CD63. Immunoprecipitation studies demonstrated protein kinase activity associated with CD63, and phosphoamino acid analysis revealed that most of this protein kinase activity was due to serine kinase activity.
  
  
  CONCLUSIONS
  The current study suggests that serine protein kinase activity associated with CD63 may play a role in signaling by CD63 in melanoma cells.
authors.affiliation: Department of Medicine, The University of Minnesota Medical School and the Masonic Cancer Center, Minneapolis, MN 55455, USA. iidax002@tc.umn.edu
authors.forename: Joji
authors.initials: J
authors.lastname: Iida
authors.forename: Amy P N
authors.initials: AP
authors.lastname: Skubitz
authors.forename: James B
authors.initials: JB
authors.lastname: McCarthy
authors.forename: Keith M
authors.initials: KM
authors.lastname: Skubitz