Activation Properties of Heterologously Expressed Mammalian TRPV2

Abstract

TRPV2 has been proposed as a potential pain target, in part due to its relatedness to the nociceptor TRPV1 and to its reported activation by noxious high temperatures (>52°C). However, TRPV2 responses to heat as well as to the nonselective agonist 2-aminoethoxydiphenyl borate (2-APB) have not been universally reproduced in other laboratories, leading to debate about the activation properties of this channel. Here, we report the expression of rat, mouse, and human TRPV2 in HEK293 cells and the differential properties of their responses to heat and 2-APB. Expression of mouse or rat TRPV2 in HEK293 cells resulted in robust channel activation when induced by either temperature (>53°C) or 2-APB. By contrast, expression of human TRPV2 did not lead to detectable activation by either of these stimuli. Human TRPV2 protein was expressed at levels comparable with those of rat TRPV2, exhibited similar surface localization and responded to a novelly identified TRPV2 agonist, ⌬ 9 -tetrahydrocannabinol, indicating that human TRPV2 is functionally expressed on the cell surface. Studies using deletion mutants and chimeras between rat and human TRPV2 indicated that both amino-and carboxyl-cytoplasmic termini of rat TRPV2 are important for responses to heat and 2-APB but can be supplied in trans to form an active channel. The present study not only confirms and extends previous reports demonstrating that rat and mouse TRPV2 respond to 2-APB and noxious heat but also indicates that further investigation will be required to elucidate TRPV2 activation and regulatory mechanisms.TRP (transient receptor potential) proteins comprise a large family of nonselective cation channels responsible for diverse cellular functions, including the transduction of thermal, chemical, and mechanical stimuli, as well as the regulation of cellular calcium levels. Named after the Drosophila phototransduction pathway mutant trp, with which they share common structural homology (1), these proteins are characterized by a six-transmembrane domain region, including a pore and cytosolically oriented NH 2 and COOH termini, the former of which typically includes one or more ankyrin domain repeats (for a review, see Ref.2). Recent studies have provided evidence that there are at least six distinct TRP channels that are temperature sensors (3). These thermo-TRPs are believed to be important transducers of temperature to the nervous system, including the sensation of pain due to noxious heat and cold. TRPV1, the most extensively characterized member of the TRP family, is activated by moderate heat (ϳ43°C), capsaicin, protons, and certain lipidic mediators, such as anandamide (4, 5). Moreover, numerous studies using a variety of experimental approaches have implicated TRPV1 in the transduction of pain signals in animal models of hyperalgesia (6, 7); hence, this TRP has been aggressively pursued as a target for the alleviation of certain types of pain.The TRP vanilloid subfamily, type 2 channel (TRPV2; also known as vanilloid receptor-like 1, or VRL-1), is closely rel...

Structure of the Full-Length TRPV2 Channel by Cryo-EM

“…The observed differences in the Ca 2 þ measurements between both truncated TRPV2 orthologues could be attributed to many different experimental variables. TRPV2 activation by 2-APB is known to be species dependent 37,38 ; therefore the response of rat TRPV2 to 2-APB may be inherently different from that of rabbit TRPV2. A parallel characterization of how 2-APB interacts with rat versus rabbit TRPV2 may provide insights into how 2-APB activates TRPV2 orthologues.…”

Modular thermal sensors in temperature-gated transient receptor potential (TRP) channels

“…Our above analyses implicated the MPD of the N terminus as a prominent structural component mediating the thermal sensitivity of TRPV1 and TRPV2. To further elucidate the significance of the region, we examined other vanilloid receptor homologues including the temperature-insensitive human isoform hTRPV2 (21). We asked whether the abnormality of hTRPV2 is due to alteration of its MPD.…”

“…Thus, the MPD of the N terminus emerged as the only component capable of perturbing the enthalpy of the channel. It is interesting that the region maps to the missing segment in the nonfunctional TRPV1b splice variant (21,27). The effectiveness of the region throughout different channels suggests that its function is conserved.…”

TRP channels in neurogastroenterology: opportunities for therapeutic intervention

“…Because heat stimuli above 52°C are highly unlikely to occur in the gut, a role in mechanosensation as proposed by Muraki is more likely in the gut (Muraki et al, 2003). However, while heat and mechano-activation of TRPV2 remain controversial, the channel is consistently activated by 2-aminoethoxydiphenyl borate and tetra-hydrocannabinol, the psychoactive compound in marijuana (Neeper et al, 2007). Future studies will have to provide insight into the role of TRPV2 in the gut.…”