Cannabinoid receptor interacting protein 1a (CRIP1a) regulates CB1 receptor trafficking

Abstract

The CB1 receptor (CB1R) is a GPCR highly expressed in the CNS and has been targeted therapeutically for multiple diseases; however, CB1 compounds have limited clinical use due to their side effect profiles. GPCR interacting proteins provide a new avenue for modulating receptor activity. The Cannabinoid Receptor Interacting Protein (CRIP1a) is an accessory protein for CB1 that reversed CB1‐mediated tonic inhibition of voltage‐gated Ca 2+ channels (Neihaus et al., 2008). The focus of this study was to investigate the cellular mechanisms underlying the CRIP1a‐CB1 interaction. CB1R was co‐immunoprecipitated from membranes and identified histochemically using antibodies developed against a non‐CB1R binding domain of CRIP1a. Stable over‐expression or knock‐down of CRIP1a in N18TG2 neuroblastomas did not alter CB1R mRNA or total protein levels. However, CB1R plasma membrane (PM) density was significantly reduced in CRIP1a over‐expressing clones, but increased in CRIP1a knock‐downs. The CB1R agonist WIN55212 led to CB1R internalization in WT and CRIP1a knock‐down cells, but a loss of internalization and a net increase in receptor externalization in CRIP1a over‐expressors. The CB1 antagonist rimonabant increased CB1R plasma membrane density in WT and CRIP1a over‐expressing and knock‐down clones. Thus, the function of CRIP1a may be to modulate trafficking and internalization‐associated CB1R mechanisms.