Differential modulation of agonist and antagonist structure activity relations for rat TRPV1 by cyclosporin A and other protein phosphatase inhibitors

Abstract

The transient receptor potential V1 channel (vanilloid receptor, TRPV1) represents a promising therapeutic target for inflammatory pain and other conditions involving C-fiber sensory afferent neurons. Sensitivity of TRPV1 is known to be subject to modulation by numerous signaling pathways, in particular by phosphorylation, and we wished to determine whether TRPV1 structure-activity relations could be differentially affected. We demonstrate here that the structure activity relations of TRPV1, as determined by 45 Ca 2+ uptake, were substantially altered by treatment of the cells with cyclosporin A, an inhibitor of protein phosphatase 2B. Whereas the potency of resiniferatoxin for stimulation of 45 Ca 2+ was not altered by cyclosporin A treatment, the potencies of some other agonists were increased up to 8-fold. Among antagonists examined, potencies were reduced to a lesser extent, ranging from 1-2.5 fold. Finally, the efficacy of partial agonists was increased. In contrast to cyclosporin A, okadaic acid, an inhibitor of protein phosphatases 1 and 2A, had little effect on agonist potencies, and calyculin A, an inhibitor of protein phosphatases 1 and 2A but with somewhat different selectivity from that of okadaic acid, caused changes in structure activity relations distinct from those induced by cyclosporin A. Because phosphatase activity differentially modulates the structure activity relations of TRPV1 agonists and antagonists, our findings predict that it may be possible to design agonist and antagonists selective for TRPV1 in a specific regulatory environment. A further implication is that it may be desirable to tailor screening approaches for drug discovery to reflect the desired regulatory state of the targeted TRPV1.

Structure‐activity relationships of vanilloid receptor agonists for arteriolar TRPV1

“…However, it was also shown, that the anandamide-mediated tachyphylaxis was antagonized by a protein phosphatase 2B (calcineurin) inhibitor (Lizanecz et al, 2006). Moreover, in accordance with this hypothesis, TRPV1 responses to agonists were differently modulated by inhibition of calcineurin in a CHO-TRPV1 cell line (Pearce et al, 2008), suggesting ligand selectivity for phosphorylation-dependent TRPV1 sensitization/ desensitization/tachyphylaxis.…”

“…Columns represent mean Ϯ SEM (n = 5), significant differences (P < 0.05) from the control (wipes upon administration of the vehicle alone) are represented by asterisks. et al, 2003) 95 Ϯ 8 nM (Pearce et al, 2008) 35 Ϯ 11 nM (Toth et al, 2005b) Toth et al, 2005b) 221 nM 58 Ϯ 7%…”

“…Resiniferatoxin 23 pM (Lee et al, 2001) 1.5 Ϯ 0.3 nM (Pearce et al, 2008) 81 Ϯ 20 pM (Toth et al, 2005b) -(Toth et al, 2005b No effect at 10 nM N/A + JYL-273 11 Ϯ 4 nM (Lee et al, 2001) 361 Ϯ 54 nM (Lee et al, 2002) No data…”

Regulation of the Benzamil-Insensitive Salt Taste Receptor by Intracellular Ca2+, Protein Kinase C, and Calcineurin

“…In addition, all rinse and stimulating solutions were supplemented with 0.01 M CaCl 2 (Table 2) . RTX-chorda tympani dose-response profiles were obtained before and after topical lingual application of KN-93, a specific blocker of CaMK II (Liu and Simon 2003) or specific inhibitors of PP2B (cyclosporin A or FK-506) (Klee et al 1998;Pearce et al 2008). As a control for KN-93, we used the kinaseinactive analog KN-92 (Table 2).…”

Structural Insight into Tetrameric hTRPV1 from Homology Modeling, Molecular Docking, Molecular Dynamics Simulation, Virtual Screening, and Bioassay Validations

“…The detailed interactions between hTRPV1/rTRPV1 and their ligands cannot therefore be ascertained with certainty, although there has been substantial work using modeled structures. 21–24 Of particular interest are the differences between TRPV1 bound with agonists and with antagonists.…”