AbstractThe receptor protein tyrosine phosphatase PTPµ belongs to a family of adhesion molecules that contain cell–cell adhesion motifs in their extracellular segments and catalytic domains within their intracellular segments. The ability of PTPµ both to mediate adhesion and exhibit enzymatic activity makes PTPµ an excellent candidate to transduce signals in response to cell–cell adhesion. In an effort to identify downstream signaling partners of PTPµ, we performed a modified yeast two‐hybrid screen using the first tyrosine phosphatase domain of PTPµ as bait. We isolated an interacting clone encoding BRCA2 and CDKN1A interacting protein (BCCIP) from a HeLa cell library. BCCIP is a p21 and BRCA2 interacting protein that has been shown to play roles in both cell cycle arrest and DNA repair. In this manuscript, we confirm the interaction between BCCIP and PTPµ identified in yeast using in vitro biochemical studies and characterize BCCIP as a PTPµ binding protein. We demonstrate that BCCIP is phosphorylated by the Src tyrosine kinase and dephosphorylated by the PTPµ tyrosine phosphatase in vitro. Furthermore, we show that BCCIP is required for both the permissive and repulsive functions of PTPµ in neurite outgrowth assays, suggesting BCCIP and PTPµ are in a common signal transduction pathway. J. Cell. Biochem. 105: 1059–1072, 2008. © 2008 Wiley‐Liss, Inc.