Interplay among Grb2, HGAL, and Syk proteins. (A) Knockdown of Syk decreases the Grb2 and HGAL interaction in co-IP experiment in unstimulated Raji cells. Bar graphs show the relative densitometry of Grb2 protein in HGAL immunoprecipitates or HGAL protein in Grb2 immunoprecipitates; western blots demonstrate expression of Syk following Syk knockdown. (B) Effect of Grb2 knockout on HGAL and Syk interaction in a co-IP experiment in unstimulated and BCR-stimulated Raji cells. Bar graphs show the relative densitometry of HGAL protein in Syk immunoprecipitates or Syk protein in HGAL immunoprecipitates. (C) Effect of HGAL knockout on Grb2 and Syk interaction in co-IP experiment in unstimulated and BCR-stimulated Raji cells. Bar graphs show the relative densitometry of Grb2 protein in Syk immunoprecipitates or Syk protein in Grb2 immunoprecipitates. (D) Syk kinase activity assay. Syk was immunoprecipitated from unstimulated or stimulated Raji cells and used in a Syk kinase activity assay, either alone or with purified HGAL and/or Grb2 proteins. Immunoprecipitates with control antibody and beads only were used as negative controls. Data in panels A-D are representative of 3 independent experiments. Error bars represent standard deviation.