Endocannabinoid signaling depends upon the CB1 and CB2 cannabinoid receptors, their endogenous ligands anandamide and 2-arachidonoylglycerol, and intracellular proteins that mediate responses via the C-terminal and other intracellular receptor domains. The CB1 receptor regulates and is regulated by associated G proteins predominantly of the Gi/o subtypes, β-arrestins 1 and 2, and the cannabinoid receptor-interacting protein 1a (CRIP1a). Evidence for a physiological role for CRIP1a is emerging as data regarding the cellular localization and function of CRIP1a are generated. Here we summarize the neuronal distribution and role of CRIP1a in endocannabinoid signaling, as well as discuss investigations linking CRIP1a to development, vision and hearing sensory systems, hippocampus and seizure regulation, and psychiatric disorders including schizophrenia. We also examine the genetic and epigenetic association of CRIP1a within a variety of cancer subtypes. This review provides evidence upon which to base future investigations on the function of CRIP1a in health and disease.

Cannabinoid receptor interacting protein 1a (CRIP1a) modulates CB 1 cannabinoid receptor G-protein coupling in part by altering the selectivity for Gα i subtype activation, but the molecular basis for this function of CRIP1a is not known. We report herein the first structure of CRIP1a at a resolution of 1.55 Å. CRIP1a exhibits a 10-stranded and antiparallel β-barrel with an interior comprised of conserved hydrophobic residues and loops at the bottom and a short helical cap at the top to exclude solvent. The β-barrel has a gap between strands β8 and β10, which deviates from β-sandwich fatty acid–binding proteins that carry endocannabinoid compounds and the Rho-guanine nucleotide dissociation inhibitor predicted by computational threading algorithms. The structural homology search program DALI identified CRIP1a as homologous to a family of lipidated-protein carriers that includes phosphodiesterase 6 delta subunit and Unc119. Comparison with these proteins suggests that CRIP1a may carry two possible types of cargo: either (i) like phosphodiesterase 6 delta subunit, cargo with a farnesyl moiety that enters from the top of the β-barrel to occupy the hydrophobic interior or (ii) like Unc119, cargo with a palmitoyl or a myristoyl moiety that enters from the side where the missing β-strand creates an opening to the hydrophobic pocket. Fluorescence polarization analysis demonstrated CRIP1a binding of an N-terminally myristoylated 9-mer peptide mimicking the Gα i N terminus. However, CRIP1a could not bind the nonmyristolyated Gα i peptide or cargo of homologs. Thus, binding of CRIP1a to Gαi proteins represents a novel mechanism to regulate cell signaling initiated by the CB 1 receptor.

Cannabinoid receptor interacting protein 1a (CRIP1a) is an 18 kDa protein that regulates the CB1 cannabinoid receptor by modifying G‐protein‐mediated signaling and competing for β‐arrestin interactions with the receptor (Booth et al., Molecules. 2019; 24: 3672). Physiological functions associated with CRIP1a include involvement in certain cancers, embryonic development, and functions of the retina (reviewed in Oliver et al., Biomolecules. 2020, 10: 1609). We determined the CRIP1a structure in an effort to elucidate CRIP1a functions. The 1.55 Å resolution crystal structure shows that CRIP1a exhibits a 10‐stranded, antiparallel b‐barrel with an interior comprised of conserved hydrophobic residues and loops at the bottom and a short helical cap at the top that serve to exclude solvent. The DALI server identified CRIP1a as homologous to a family of lipidated protein‐carriers. Based upon this structural knowledge, we tested the hypothesis that CRIP1a could serve as a carrier of lipidated proteins from cytosol to membranes. Using a mouse neuroblastoma N18TG2 cultured cell model, homogenates were sedimented, and cytosolic and membrane fractions were subjected to SDS‐page electrophoresis and western analysis. We determined that CRIP1a is found in both cytosolic and membrane fractions. Immunoprecipitations using a CRIP1a antibody in the absence of detergents showed an apparent molecular weight shift for CRIP1a upon western blot analysis compared with purified, recombinant CRIP1a or CRIP1a in detergent extracts. The molecular weight shift in CRIP1a suggests the formation of a complex or interaction with other cellular proteins consistent with a role for CRIP1a in trafficking of cargo proteins.

Type II diabetes mellitus and non‐alcoholic fatty liver disease are two examples of metabolic diseases that are contributing to the emerging health crisis in the west. Key to understanding these diseases and their progression is an understanding of neutral lipid metabolism. Perilipins are a class of five conserved proteins that are key regulators of lipid metabolism and are potentially involved in lipid trafficking within cells. The most recently discovered member of the family is perilipin 5, which is expressed most strongly in tissues that are highly oxidative such as heart, oxidative muscle, and fasting liver. Perilipin 5 is predominantly located on the surface of lipid storage droplets, but has also been found in the cytoplasm, nucleus, and the endoplasmic reticulum and mitochondria. We hypothesized that perilipin 5 moves between these cellular pools via interactions with other proteins. Furthermore, we hypothesized that interactions with Rabs were necessary for this trafficking to occur. CHO cells ectopically expressing perilipin 5 and endogenously expressing Rab18 were assayed using western blotting. These proteins were found in the same cellular pools. Immunoprecipitations are being used to assay for interactions between perilipin 5, Rab18, and Rab32. Immunofluorescence microscopy indicates that perilipin 5 and Rabs colocalize to the same cellular pools. Collectively these data will provide a more detailed picture of perilipin 5 in the cell.Support or Funding InformationOtterbein University Student Research FundThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Type II diabetes mellitus and non‐alcoholic fatty liver disease are two examples of metabolic diseases that are reaching epidemic proportions in the US. Key to understanding these diseases and their progression is an understanding of neutral lipid metabolism. Perilipins are a class of five conserved proteins that are key regulators of lipid metabolism and are potentially involved in lipid trafficking within cells. The most recently discovered member of the family is perilipin 5, which is expressed most strongly in tissues that are highly oxidative such as heart, oxidative muscle, and fasting liver. Perilipin 5 is predominantly located on the surface of lipid storage droplets, but has also been found in the cytoplasm, nucleus, and the endoplasmic reticulum and mitochondria. We hypothesized that perilipin 5 moves between these cellular pools via interactions with other proteins. Furthermore, we hypothesized that interactions with Rabs were necessary for this trafficking to occur. CHO cells expressing perilipin 5 were assayed using western blotting and were found to express Rab 18. Immunoprecipitations are being used to assay for interactions between perilipin 5, Rab 18, and other proteins. Collectively these data will provide a more detailed picture of perilipin 5 in the cell.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.