The GABA rho1 subunit interacts with a cellular retinoic acid binding protein in mammalian retina.

Interactions between the intracellular domain of ligand-gated membrane receptors and cytoplasmic proteins play important roles in their assembly, clustering, and function. In addition, protein-protein interactions may provide an alternative mechanism by which neurotransmitters activate intracellular pathways. In this study, we report a novel interaction between the GABA rho1 subunit and cellular retinoic acid binding protein in mammalian retina that could serve as a link between the GABA signaling pathway and the control of gene expression in neurons. The interaction between the intracellular loop of the human GABA rho subunit and cellular retinoic acid binding protein was identified using a CytoTrap XR yeast two-hybrid system, and was further confirmed by co-precipitation of the human GABA rho subunit and cellular retinoic acid binding protein from baboon retinal samples. The cellular retinoic acid binding protein binding domain on the human rho1 subunit was located to the C-terminal region of human GABA rho subunit, and the interaction of the human GABA rho subunit with cellular retinoic acid binding protein could be antagonized by a peptide derived from within the binding domain of the rho1 subunit. Since cellular retinoic acid binding protein is a carrier protein for retinoic acid, we investigated the effect of GABA on retinoic acid activity in neuroblastoma cells containing endogenously expressed cellular retinoic acid binding protein. In the absence of the rho1 receptor, these cells showed enhanced neurite outgrowth when exposed to retinoic acid and GABA had no effect on their response to retinoic acid. In contrast, cells stably transfected with the human rho1 subunit showed a significantly reduced sensitivity to retinoic acid when exposed to GABA. These results suggest that the GABA receptor subunit effectively altered gene expression through its interaction with the cellular retinoic acid binding protein pathway.