Signaling complex formation of phospholipase Cβ4 with metabotropic glutamate receptor type 1α and 1,4,5-trisphosphate receptor at the perisynapse and endoplasmic reticulum in the mouse brain

Upon activation of cell surface receptors coupled to the Gq subclass of G proteins, phospholipase C (PLC) β hydrolyses membrane phospholipid to yield a pair of second messengers, inositol 1,4,5-trisphosphate (IP₃) and 1,2-diacylglycerol. PLCβ4 has been characterized as the isoform enriched in cerebellar Purkinje cells (PCs) and the retina and involved in motor and visual functions. Here we examined cellular and subcellular distributions of PLCβ4 in adult mouse brains. Immunohistochemistry showed that high levels of PLCβ4 were detected in the somatodendritic domain of neuronal populations expressing the metabotropic glutamate receptor (mGluR) type 1α, including olfactory periglomerular cells, neurons in the bed nucleus anterior commissure, thalamus, substantia nigra, inferior olive, and unipolar brush cells and PCs in the cerebellum. Low to moderate levels were detected in many other mGluR1α-positive neurons and in a few mGluR1α-negative neurons. In PCs, immunogold electron microscopy localized PLCβ4 to the perisynapse, at which mGluR1α is concentrated, and to the smooth endoplasmic reticulum in dendrites and spines, an intracellular Ca²⁺ store gated by IP₃ receptors. In the cerebellum, immunoblot demonstrated its concentrated distribution in the post-synaptic density and microsomal fractions, where mGluR1α and type 1 IP₃ receptor were also greatly enriched. Furthermore, PLCβ4 formed coimmunoprecipitable complexes with mGluR1α, type 1 IP₃ receptor and Homer 1. These results suggest that PLCβ4 is preferentially localized in the perisynapse and smooth endoplasmic reticulum as a component of the physically linked phosphoinositide signaling complex. This close molecular relationship might provide PLCβ4 with a high-fidelity effector function to mediate various neuronal responses under physiological and pathophysiological conditions.