Molecular pharmacology of the onco-TRP channel TRPV6

Abstract

TRPV6, a representative of the vanilloid subfamily of TRP channels, serves as the principal calcium uptake channel in the gut. Dysregulation of TRPV6 results in disturbed calcium homeostasis leading to a variety of human diseases, including many forms of cancer. Inhibitors of this oncochannel are therefore particularly needed. In this review, we provide an overview of recent advances in structural pharmacology that uncovered the molecular mechanisms of TRPV6 inhibition by a variety of small molecules, including synthetic and natural, plant-derived compounds as well as some prospective and clinically approved drugs.

Keywords: TRP channels; TRPV6; cancer; cryo-EM; inhibitor; structural biology.

Figure 1.

TRPV6 architecture and domain organization. a, side (left) and top (right) views of human TRPV6 tetramer (PDB ID: 7S88), with subunits (A-D) shown in different colors (green, yellow, red, and blue). b, a single TRPV6 subunit, with domains shown in different colors and labeled. Adapted from [62].

Figure 2.

Activation of TRPV6 by PIP₂. a, side (left) and bottom (right) views of the open, apo-state hTRPV6 (PDB ID: 7S88), with subunits (A-D) colored green, yellow, red, and blue, and PIP₂ molecules (space-filling models) projected from the PIP₂-bound structure of TRPV5 (PDB ID: 6DMU). b, expanded view of the PIP₂ binding site, with the PIP₂ molecule and residues surrounding the head group of PIP₂ shown as stick models. Adapted from [71,72].

Figure 3.

Structure of inactivated TRPV6 in complex with calmodulin. a, side (left) and bottom (right) views of hTRPV6-CaM complex (PDB ID: 6E2F), with hTRPV6 subunits (A-D) colored green, yellow, red, and blue and CaM colored purple. Calcium ions are shown as green spheres. Side chains of hTRPV6 residues W583, CaM residue K115 and those that coordinate calcium ions are shown as sticks. b, side view of hTRPV6-CaM, with only two of four subunits shown and the front and back subunits removed for clarity. c, expanded view of the intracellular pore entrance, with CaM residue K115 forming a unique cation–π interaction with the cubic cage of side chain indoles contributed by W583 from each TRPV6 subunit. Adapted from [14].

Figure 4.

Inactivation-mimicking block of TRPV6 by PCHPDs. a, side view of hTRPV6_cis-22a structure, with hTRPV6 subunits (A-D) colored green, yellow, red, and blue and the PCHPD cis-22a molecules shown as space-filling models (violet). b,c, pore-forming domains in hTRPV6_cis-22a (b, PDB ID: 7K4B) and hTRPV6-CaM (c, PDB ID: 6E2F). Only two of four hTRPV6 subunits are shown, with the front and back subunits removed for clarity. The region undergoing α-to-π transition in the middle of S6 is colored pink. The molecule of cis-22a (b, violet), CaM residue K115 (c, purple) and TRPV6 residues around the gate are shown as stick models. d – f, hTRPV6 ion conduction pathway (gray) in the open-state structure hTRPV6_apo (d, PDB ID: 7K4A) and inactivated-state structures hTRPV6_cis-22a (e, PDB ID: 7K4B) and hTRPV6-CaM (f, PDB ID: 6E2F). The gate region is indicated by green arrows. Adapted from [64].

Figure 5.

Structures of TRPV6 in complex with synthetic inhibitors RR, 2-APB and econazole. a, side (left), top (middle), and bottom (right) views of hTRPV6_RR (PDB ID: 7S8B), with hTRPV6 subunits (A-D) colored green, yellow, red, and blue. The RR molecule is shown as a ball-and-stick model, with the corresponding cryo-EM density shown as red mesh and Ca²⁺ ion as a green sphere. Molecules of 2-APB (dark green) from hTRPV6_2-APB (PDB ID: 6D7T) and econazole (cyan) from hTRPV6_Eco (PDB ID: 7S8C) are shown as space-filling models. b,d,f, expanded views of the RR (b), 2-APB (d) and econazole (f) binding sites. RR molecule is shown the same way as in a. Molecules of 2-APB (dark green) and econazole (cyan) as well as residues contributing to inhibitor binding are shown as stick models. c,e,g, ion conduction pathway (gray) in hTRPV6 bound to RR (c), 2-APB (e) and econazole (g), with residues lining the selectivity filter and around the gate shown as stick models. Only two of four subunits are shown, with the front and back subunits removed for clarity. The region undergoing α-to-π transition in the middle of S6 is colored pink. The gate region is indicated by green arrows. Adapted from [65,89].

Figure 6.

Structures of TRPV6 in complex with natural inhibitors THCV and genistein. a, side (left) and top (right) views of hTRPV6_Gen (PDB ID: 8FOA), with hTRPV6 subunits (A-D) colored green, yellow, red, and blue. Molecules of genistein (brown) and THCV (purple) from hTRPV6_THCV (PDB ID: 8SP8) are shown as space-filling models. b,d, expanded views of the THCV (b) and genistein (d) binding sites. THCV (purple) and genistein (brown) molecules are shown as stick models. c,e, ion conduction pathway (gray) in hTRPV6 bound to THCV (c) and genistein (e), with residues lining the selectivity filter and around the gate shown as stick models. Only two of four subunits are shown, with the front and back subunits removed for clarity. The region undergoing α-to-π transition in the middle of S6 is colored pink. The gate region is indicated by green arrows. Adapted from [66,110].

Figure 7.

Pore radius in the closed, open and inactivated states. Pore radius calculated using HOLE [167] for hTRPV6 in the open (orange; PDB ID: 7K4A), inactivated by CaM (light green, PDB ID: 6E2F) and cis-22a (dark green, PDB ID: 7K4B), and closed (shades of blue, from light to dark, for RR, PDB ID: 7S8B; 2-APB, PDB ID: 6D7T; econazole, PDB ID: 7S8C; genistein, PDB ID: 8FOA; THCV, PDB ID: 8SP8; R470E mutant, PDB ID: 6BOA) states. Adapted from [14,63–66,89,110].