PIK3AP1 is involved in the activation of phosphoinositide 3-kinase (PI3K) in B-cells and in natural killer (NK) cells. It couples B-cell antigen receptor (BCR) to PI3K activation by providing a docking site for the PI3K subunit PIK3R1, which contributes to B-cell development. PIK3AP1 seems to have a complementary role with CD19 in PI3K activation (By similarity) and is may be involved in the survival of mature B cells via activation of REL (By similarity).Synonyms: B-cell adapter for phosphoinositide 3-kinase, BCAP, Phosphoinositide 3-kinase adapter protein 1