Extracellular modulation of TREK-2 activity with nanobodies provides insight into the mechanisms of K2P channel regulation.

Potassium channels of the Two-Pore Domain (K2P) subfamily, KCNK1-KCNK18, play crucial roles in controlling the electrical activity of many different cell types and represent attractive therapeutic targets. However, the identification of highly selective small molecule drugs against these channels has been challenging due to the high degree of structural and functional conservation that exists not only between K2P channels, but across the whole K+ channel superfamily. To address the issue of selectivity, here we generate camelid antibody fragments (nanobodies) against the TREK-2 (KCNK10) K2P K+ channel and identify selective binders including several that directly modulate channel activity. X-ray crystallography and CryoEM data of these nanobodies in complex with TREK-2 also reveal insights into their mechanisms of activation and inhibition via binding to the extracellular loops and Cap domain, as well as their suitability for immunodetection. These structures facilitate design of a biparatropic inhibitory nanobody with markedly improved sensitivity. Together, these results provide important insights into TREK channel gating and provide an alternative, more selective approach to modulation of K2P channel activity via their extracellular domains.

Pid1 induces insulin resistance in both human and mouse skeletal muscle during obesity.

Obesity is associated with insulin resistance and abnormal peripheral tissue glucose uptake. However, the mechanisms that interfere with insulin signaling and glucose uptake in human skeletal muscle during obesity are not fully characterized. Using microarray, we have identified that the expression of Pid1 gene, which encodes for a protein that contains a phosphotyrosine-interacting domain, is increased in myoblasts established from overweight insulin-resistant individuals. Molecular analysis further validated that both Pid1 mRNA and protein levels are increased in cell culture models of insulin resistance. Consistent with these results, overexpression of phosphotyrosine interaction domain-containing protein 1 (PID1) in human myoblasts resulted in reduced insulin signaling and glucose uptake, whereas knockdown of PID1 enhanced glucose uptake and insulin signaling in human myoblasts and improved the insulin sensitivity following palmitate-, TNF-α-, or myostatin-induced insulin resistance in human myoblasts. Furthermore, the number of mitochondria in myoblasts that ectopically express PID1 was significantly reduced. In addition to overweight humans, we find that Pid1 levels are also increased in all 3 peripheral tissues (liver, skeletal muscle, and adipose tissue) in mouse models of diet-induced obesity and insulin resistance. An in silico search for regulators of Pid1 expression revealed the presence of nuclear factor-κB (NF-κB) binding sites in the Pid1 promoter. Luciferase reporter assays and chromatin immunoprecipitation studies confirmed that NF-κB is sufficient to transcriptionally up-regulate the Pid1 promoter. Furthermore, we find that myostatin up-regulates Pid1 expression via an NF-κB signaling mechanism. Collectively these results indicate that Pid1 is a potent intracellular inhibitor of insulin signaling pathway during obesity in humans and mice.