May regulate the transport and translation of mRNAs of proteins involved in synaptic plasticity in neurons and cell proliferation and migration in multiple cell types (PubMed:20516077). Binds directly and selectively to MYC and CCND2 RNAs. In neuronal cells, directly binds to several mRNAs associated with RNA granules, including BDNF, CAMK2A, CREB1, MAP2, NTRK2 mRNAs, as well as to GRIN1 and KPNB1 mRNAs, but not to rRNAs (By similarity). May form homomultimers (PubMed:14764709). Interacts with G3BP1; interaction is direct and takes place in cytoplasmic RNA granules (PubMed:17210633). Interacts with PQBP1 (By similarity). Interacts with DDX3X (By similarity). Associated with RNA granules (PubMed:17210633). At the leading edge of migrating fibroblasts, colocalizes with DDX3X (By similarity). Highest expression in thymus, spleen and brain (at protein level). Lower levels in kidney, muscle and liver (at protein level). Up-regulated when resting T- or B-lymphocytes or hemopoietic progenitors are activated. Down-regulated when a monocytic leukemia cell line, M1, is induced to differentiate. Expressed in brain at 17.5 dpc (at protein level). O-glycosylated (O-GlcNAcylated), in a cell cycle-dependent manner. Belongs to the caprin family. Was originally thought to be a GPI-anchored membrane protein. Truncated N-terminus.