RhoBTB3 interacts with the 5-HT7a receptor and inhibits its proteasomal degradation.

The 5-hydroxytryptamine (5-HT)7 receptor is the most recently identified serotonin receptor and is involved in a wide variety of central nervous system (CNS) functions, namely circadian rhythm, REM sleep, depression, thermoregulation, obsessive-compulsive disorder (OCD), anxiety, schizophrenia, epilepsy, nociception, migraine, sensation-seeking behavior, impulsivity, learning and memory. These numerous (patho)physiological processes of the CNS, in which the 5-HT7 receptor is involved, most likely reflect a diverse set of signaling pathways arising from this receptor. In order to reveal new interaction partners and possibly new signaling and/or trafficking pathways, we performed a yeast two-hybrid screening, using the C-terminal tail of the 5-HT7a receptor as bait and an adult-human brain cDNA library as prey. In this way we identified RhoBTB3 as a new interaction partner of the 5-HT7a receptor. By means of co-immunoprecipitation we were able to confirm the interaction between full length 5-HT7a receptor and RhoBTB3 in HEK293T cells. Subsequent domain mapping of this interaction revealed that not only the C-terminal tail, but also the third intracellular loop of the 5-HT7a receptor is involved. In addition, immunofluorescence microscopy showed clear co-localization between the 5-HT7a receptor and RhoBTB3 at the plasma membrane and in the endoplasmic reticulum. Despite the fact that RhoBTB3 has been shown to interact with Cul3, which in turn interacts with the E3 ubiquitin ligase, Roc1, we show here that RhoBTB3 neither recruits Cul3/Roc1 to the 5-HT7a receptor nor does it mediate ubiquitination of this receptor. Instead, we demonstrate that RhoBTB3 strongly inhibits proteasomal degradation of the 5-HT7a receptor.

Role of the 5-HT7 receptor in the central nervous system: from current status to future perspectives.

Pharmacological and genetic tools targeting the 5-hydroxytryptamine (5-HT)7 receptor in preclinical animal models have implicated this receptor in diverse (patho)physiological processes of the central nervous system (CNS). Some data obtained with 5-HT7 receptor knockout mice, selective antagonists, and, to a lesser extent, agonists, however, are quite contradictory. In this review, we not only discuss in detail the role of the 5-HT7 receptor in the CNS but also propose some hypothetical models, which could explain the observed inconsistencies. These models are based on two novel concepts within the field of G protein-coupled receptors (GPCR), namely biphasic signaling and G protein-independent signaling, which both have been shown to be mediated by GPCR dimerization. This led us to suggest that the 5-HT7 receptor could reside in different dimeric contexts and initiate different signaling pathways, depending on the neuronal circuitry and/or brain region. In conclusion, we highlight GPCR dimerization and G protein-independent signaling as two promising future directions in 5-HT7 receptor research, which ultimately might lead to the development of more efficient dimer- and/or pathway-specific therapeutics.

Cloning, genomic organization and functionality of 5-HT(7) receptor splice variants from mouse brain.

The serotonin (5-HT) 5-HT(7) receptors are expressed in both the central nervous system and in peripheral tissues. Receptor distribution studies and pharmacological studies have established that 5-HT(7) receptors play an important role in the control of circadian rhythms and thermoregulation. Selective 5-HT(7) receptor ligands have potential therapeutic applications for the treatment of pain and migraine, schizophrenia, anxiety, cognitive disturbances and inflammation. We have cloned two novel C-terminal splice variants of the 5-HT(7) receptor from mouse brain. These two new splice variants have almost identical sequences as the rat 5-HT(7(b)) and 5-HT(7(c)) splice variants and so were given the same name. Ligand binding assays ([(3)H]5-CT), membrane localization and functional studies in transiently transfected cells indicated that all three splice variants are well expressed on the membrane and no major differences in their respective pharmacology and their ability to activate adenylyl cyclase were observed. This is in analogy with previous reports comparing either the rat or the human variants.