Anatomical and ultrastructural study of PRAF2 expression in the mouse central nervous system

Abstract

Prenylated Rab acceptor family, member 2 (PRAF2) is a four transmembrane domain protein of 19 kDa that is highly expressed in particular areas of mammalian brains. PRAF2 is mostly found in the endoplasmic reticulum (ER) of neurons where it plays the role of gatekeeper for the GB1 subunit of the GABA receptor, preventing its progression in the biosynthetic pathway in the absence of hetero-dimerization with the GB2 subunit. However, PRAF2 can interact with several receptors and immunofluorescence studies indicate that PRAF2 distribution is larger than the ER, suggesting additional biological functions. Here, we conducted an immuno-cytochemical study of PRAF2 distribution in mouse central nervous system (CNS) at anatomical, cellular and ultra-structural levels. PRAF2 appears widely expressed in various regions of mature CNS, such as the olfactory bulbs, cerebral cortex, amygdala, hippocampus, ventral tegmental area and spinal cord. Consistent with its regulatory role of GABA receptors, PRAF2 was particularly abundant in brain regions known to express GB1 subunits. However, other brain areas where GB1 is expressed, such as basal ganglia, thalamus and hypothalamus, contain little or no PRAF2. In these areas, GB1 subunits might reach the cell surface of neurons independently of GB2 to exert biological functions distinct from those of GABA receptors, or be regulated by other gatekeepers. Electron microscopy studies confirmed the localization of PRAF2 in the ER, but identified previously unappreciated localizations, in mitochondria, primary cilia and sub-synaptic region. These data indicate additional modes of GABA regulation in specific brain areas and new biological functions of PRAF2.

Control of CCR5 Cell-Surface Targeting by the PRAF2 Gatekeeper

“…As for GB1 and CFTR, CCR5 retention is dependent on PRAF2 concentration. Previous mapping of endogenous PRAF2 distribution revealed a marked variability in PRAF2 expression in the brain, with PRAF2 being virtually absent in some areas, whereas other areas displayed very strong PRAF2 expression [19]. Moreover, PRAF2 overexpression has been reported in multiple cancers [18,33].…”

“…The shielding of the GB1 retention signal via a coiled-coil interaction with the carboxyterminal of GB2 allows the hetero-dimer to reach the cell surface [13]. We reported that Prenylated Rab Acceptor Family member 2 (PRAF2), a ubiquitous membrane-associated protein [18] particularly abundant in the ER [19], was the gatekeeper that retains GB1 in the ER via the recognition of its RXR-di-leucine signal [20]. PRAF2 tightly controls cell-surface GABA B density in vitro and in vivo [20].…”

Pharmacological chaperone-rescued cystic fibrosis CFTR-F508del mutant overcomes PRAF2-gated access to endoplasmic reticulum exit sites

“…Arginine-based (RXR) retention motifs, which supposedly mediate cargo interaction with putative ER resident gatekeepers, were identified in inwardly rectifying potassium channels [7] and in the GB1 subunit of the GABA B receptor [8]. We previously found that the Prenylated Rab Acceptor Family member 2 (PRAF2), an ubiquitous membrane-associated protein [9] particularly abundant in the ER [10], was the gatekeeper that retains the GB1 GABA B receptor subunit in the ER via the recognition of a specific RXRdi-leucine (LL) motif [11]. PRAF2 tightly controls cell-surface GABA B density and function in neurons, but its precise point of impact within the secretory pathway remained unknown.…”

PRAF2 overexpression predicts poor prognosis and promotes tumorigenesis in esophageal squamous cell carcinoma

“…Prenylated Rab acceptor 1 domain family, member 2 (PRAF2, also called JM4), a 178 amino acid endoplasmic reticulum (ER)-resident protein, comprise a prenylated Rab acceptor motif and four transmembrane domains [8, 9]. PRAF2, which is strongly expressed in human normal tissues [10], has been identified as a novel protein involved in ER-to-Golgi transport and vesicular traffic [11–13].…”