Opposing roles of E3 ligases TRIM23 and TRIM21 in regulation of ion channel ANO1 protein levels

Insights into the function and regulation of the calcium-activated chloride channel TMEM16A

The TMEM16A channel, a member of the TMEM16 protein family comprising chloride (Cl-) channels and lipid scramblases, is activated by the free intracellular Ca2+ increments produced by inositol 1,4,5-trisphosphate (IP3)-induced Ca2+ release after GqPCRs or Ca2+ entry through cationic channels. It is a ubiquitous transmembrane protein that participates in multiple physiological functions essential to mammals' lives. TMEM16A structure contains two identical 10-segment monomers joined at their transmembrane segment 10. Each monomer harbours one independent hourglass-shaped pore gated by Ca2+ ligation to an orthosteric site adjacent to the pore and controlled by two gates. The orthosteric site is created by assembling negatively charged glutamate side chains near the pore´s cytosolic end. When empty, this site generates an electrostatic barrier that controls channel rectification. In addition, an isoleucine-triad forms a hydrophobic gate at the boundary of the cytosolic vestibule and the inner side of the neck. When the cytosolic Ca2+ rises, one or two Ca2+ ions bind to the orthosteric site in a voltage (V)-dependent manner, thus neutralising the electrostatic barrier and triggering an allosteric gating mechanism propagating via transmembrane segment 6 to the hydrophobic gate. These coordinated events lead to pore opening, allowing the Cl- flux to ensure the physiological response. The Ca2+-dependent function of TMEM16A is highly regulated. Anions with higher permeability than Cl- facilitate V dependence by increasing the Ca2+ sensitivity, intracellular protons can replace Ca2+ and induce channel opening, and phosphatidylinositol 4,5-bisphosphate bound to four cytosolic sites likely maintains Ca2+ sensitivity. Additional regulation is afforded by cytosolic proteins, most likely by phosphorylation and protein-protein interaction mechanisms.

Novel marine natural products as effective TRPV1 channel blockers

Chronic pain management poses a formidable challenge to healthcare, exacerbated by current analgesic options' limitations and adverse effects. Transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel, has emerged as a promising target for novel analgesics. However, safety and tolerability concerns have constrained the development of TRPV1 modulators. In this study, we explored marine-derived natural products as a source of potential TRPV1 modulators using high-throughput dye-uptake assays. We identified chrexanthomycins, a family of hexacyclic xanthones, exhibited potent TRPV1 inhibitory effects, with compounds cC and cF demonstrating the most significant activity. High-resolution patch-clamp assays confirmed the direct action of these compounds on the TRPV1 channel. Furthermore, in vivo assays revealed that cC and cF effectively suppressed capsaicin-induced pain sensation in mice, comparable to the known TRPV1 inhibitor, capsazepine. Structural-activity relationship analysis highlighted the importance of specific functional groups in modulating TRPV1 activity. Our findings underscore the therapeutic potential of chrexanthomycins and pave the way for further investigations into marine-derived TRPV1 modulators for pain management.

Loss-of-Function Piezo1 Mutations Display Altered Stability Driven by Ubiquitination and Proteasomal Degradation

Missense mutations in the gene that encodes for the mechanically-gated ion channel Piezo1 have been linked to a number of diseases. Gain-of-function variants are linked to a hereditary anaemia and loss-of-function variants have been linked to generalized lymphatic dysplasia and bicuspid aortic valve. Two previously characterized mutations, S217L and G2029R, both exhibit reduced plasma membrane trafficking. Here we show that both mutations also display reduced stability and higher turnover rates than wild-type Piezo1 channels. This occurs through increased ubiquitination and subsequent proteasomal degradation. Congruent with this, proteasome inhibition using N-acetyl-l-leucyl-l-leucyl-l-norleucinal (ALLN) reduced the degradation of both mutant proteins. While ALLN treatment could not rescue the function of S217L we show via multiple complementary methodologies that proteasome inhibition via ALLN treatment can not only prevent G2029R turnover but increase the membrane localized pool of this variant and the functional Piezo1 mechanosensitive currents. This data in combination with a precision medicine approach provides a new potential therapeutic avenue for the treatment of Piezo1 mediated channelopathies.