Calcium-dependent phospholipid-binding protein that plays a role in ERBB2-mediated tumor cell migration in response to growth factor heregulin stimulation (PubMed:20010870). Monomer (PubMed:12949241). Interacts with ERBB2 (preferentially with the tyrosine phosphorylated form); this interaction occurs at the cell membrane and is increased in a growth factor heregulin-dependent manner (PubMed:20010870). Interacts with SHC1; this interaction may mediate the binding of CPNE3 with ERBB2 (PubMed:20010870). Interacts with RACK1 (PubMed:20010870). Associates to the membrane in a calcium-dependent manner (PubMed:20010870). Translocates to the cell membrane and the nucleus in a calcium- or growth factor heregulin-dependent manner (PubMed:21087455, PubMed:20010870). Colocalizes with the tyrosine phosphorylated ERBB2 form at cell membrane and focal adhesions in a calcium- or growth factor heregulin-dependent manner (PubMed:20010870). Expressed in breast and weakly in prostate and ovarian tissues (PubMed:20010870). Expressed in neutrophils (at protein level) (PubMed:12949241). Widely expressed (PubMed:11041869). Expressed in the brain. Expressed in neutrophil precursors from the bone marrow and peripheral blood (PubMed:12949241). Expressed in primary breast tumors and ovarian endometrioid adenocarcinoma (PubMed:20010870). Phosphorylated on serine and threonine residues (PubMed:11041869). Belongs to the copine family. Was reported to have a protein kinase activity.