Phosphoinositide-3-Kinase Adaptor Protein 1 (PIK3AP1)

Using an affinity purification strategy with the N-terminal SH2 domain of the phosphoinositide 3-kinase (PI3K) p85 subunit and anti-phosphotyrosine antibody, followed by screening a chicken DT40 B-cell cDNA library and a mouse spleen cDNA library, Okada et al. (2000) isolated cDNAs encoding chicken and mouse Pik3ap1, which they called Bcap. They also identified Bcap splice variants. Northern blot analysis of mouse tissues detected expression predominantly in spleen, with lower levels in thymus, liver, and lung. Expression was also detected in mouse macrophage and B-cell lines, but not in T-cell, plasma cell, or mast cell lines.Using mouse and chicken B- cell lines, Okada et al. (2000) determined that Bcap is a protein tyrosine kinase substrate that couples B-cell receptor to PI3K activation.