Mutations in the human gene encoding connexin 26 (Cx26 or GJB2) cause either nonsyndromic deafness or syndromic deafness associated with skin diseases. That distinct clinical disorders can be caused by different mutations within the same gene suggests that different channel activities influence the ear and skin. Here we use three different expression systems to examine the functional characteristics of two Cx26 mutations causing either mild (Cx26-D50A) or lethal (Cx26-A88V) keratitis-ichthyosis-deafness (KID) syndrome. In either cRNA-injected Xenopus oocytes, transfected HeLa cells, or transfected primary human keratinocytes, we show that both Cx26-D50A and Cx26-A88V form active hemichannels that significantly increase membrane current flow compared with wild-type Cx26. This increased membrane current accelerated cell death in low extracellular calcium solutions and was not due to increased mutant protein expression. Elevated mutant hemichannel currents could be blocked by increased extracellular calcium concentration. These results show that these two mutations exhibit a shared gain of functional activity and support the hypothesis that increased hemichannel activity is a common feature of human Cx26 mutations responsible for KID syndrome.

Mutations in GJB2 (Cx26) cause either deafness, or deafness associated with skin diseases. That different disorders can be caused by distinct mutations within the same gene suggests that unique channel activities are influenced by each class of mutation. We have examined the functional characteristics of two human mutations, Cx26-H73R and Cx26-S183F, causing palmoplantar keratoderma (PPK) and deafness. Both failed to form gap junction channels or hemichannels when expressed alone. Co-expression of the mutants with wild-type Cx43 showed a trans-dominant inhibition of Cx43 gap junction channels, without reductions in Cx43 protein synthesis. In addition, the presence of mutant Cx26 shifted Cx43 channel gating and kinetics towards a more Cx26-like behavior. Co-immunoprecipitation showed Cx43 being pulled down more efficiently with mutant Cx26, than wild-type, confirming the enhanced formation of heteromeric connexons. Finally, the formation of heteromeric connexons resulted in significantly increased Cx43 hemichannel activity in the presence of Cx26 mutants. These findings suggest a common mechanism whereby Cx26 mutations causing PPK and deafness trans-dominantly influence multiple functions of wild-type Cx43. They also implicate a role for aberrant hemichannel activity in the pathogenesis of PPK, and further highlight an emerging role for Cx43 in genetic skin diseases.

Statistics. Results are mean ± SEM. For multiple group comparisons, 1-way ANOVA followed by multiple comparison testing was performed. For comparisons between 2 groups, an unpaired Student's t test was used. Statistical analyses were performed using Prism 6 (Graphpad Software). Differences were considered statistically significant at P values less than 0.05. Data availability. The data and study materials will be made available to other researchers for purposes of reproducing the results or replicating the procedure. Study approval. The Institutional Animal Care and Use Committee at Columbia University approved all animal experiments.

Ecological interactions between different species are not fixed, but they may depend, at least to some extent, on the particular genotypes involved as well as on the environmental conditions experienced by previous generations. We used a set of natural genotypes of Arabidopsisthaliana, that previously experienced contrasting nutrient and herbivory conditions, to test for the influences of genetic variation and maternal effects on competitive interactions between Arabidopsis and the weedy annuals Anagallisarvensis and Senecio vulgaris. We used activated carbon to discriminate between resource competition and allelopathy components of plant‐plant interactions. There was a clear competitive hierarchy: Senecio>Arabidopsis>Anagallis. Although we found no evidence for allelopathic potential of Arabidopsis, our results indicate that both Anagallis and Senecio exerted negative (direct or indirect) allelopathic effects on Arabidopsis. There were significant differences among Arabidopsis genotypes in their competitive effects on both neighbor species, as well as in their response to competition. Maternal environments significantly influenced not only the growth and fitness of Arabidopsis itself, but also its competitive effect on Anagallis. We found, however, no evidence that maternal environments affected the competitive effect on Senecio or overall competitive response of Arabidopsis. Generally, resource competition played a greater role than allelopathy, and genotype effects were more important than maternal effects. Our study demonstrates that ecological interactions, such as plant competition, are complex and multi‐layered, and that, in particular, the influence of genetic variation on interactions with other species should not be overlooked.

Inhibition of voltage-gated calcium (CaV) channels is a potential therapy for many neurological diseases including chronic pain. Neuronal CaV1/CaV2 channels are composed of α, β, γ and α2δ subunits. The β subunits of CaV channels are cytoplasmic proteins that increase the surface expression of the pore-forming α subunit of CaV. We targeted the high-affinity protein–protein interface of CaVβ's pocket within the CaVα subunit. Structure-based virtual screening of 50,000 small molecule library docked to the β subunit led to the identification of 2-(3,5-dimethylisoxazol-4-yl)-N-((4-((3-phenylpropyl)amino)quinazolin-2-yl)methyl)acetamide (IPPQ). This small molecule bound to CaVβ and inhibited its coupling with N-type voltage-gated calcium (CaV2.2) channels, leading to a reduction in CaV2.2 currents in rat dorsal root ganglion sensory neurons, decreased presynaptic localization of CaV2.2 in vivo, decreased frequency of spontaneous excitatory postsynaptic potentials and miniature excitatory postsynaptic potentials, and inhibited release of the nociceptive neurotransmitter calcitonin gene–related peptide from spinal cord. IPPQ did not target opioid receptors nor did it engage inhibitory G protein–coupled receptor signaling. IPPQ was antinociceptive in naive animals and reversed allodynia and hyperalgesia in models of acute (postsurgical) and neuropathic (spinal nerve ligation, chemotherapy- and gp120-induced peripheral neuropathy, and genome-edited neuropathy) pain. IPPQ did not cause akinesia or motor impairment, a common adverse effect of CaV2.2 targeting drugs, when injected into the brain. IPPQ, a quinazoline analog, represents a novel class of CaV2.2-targeting compounds that may serve as probes to interrogate CaVα–CaVβ function and ultimately be developed as a nonopioid therapeutic for chronic pain.

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SignificanceInflux of calcium ions through surface membrane calcium channels that open in response to electrical signals is important for vital biological processes including generation of the heartbeat and nerve cell communication. Blocking such calcium channels in a tissue- and isoform-specific manner is a sought-after treatment strategy for diseases including chronic pain and Parkinson’s disease. Proteins that can be expressed in cells to selectively block different calcium channel types have particular advantages over conventional small-molecule blockers. A four-member family of proteins known as RGK proteins strongly inhibit calcium channels, but do so in a non-selective manner, limiting their potential usefulness. Here we identified mutated RGK proteins that perform as isoform-selective calcium channel blockers, advancing the therapeutic potential of these proteins.

Cav1.2 channels in the heart mediate excitation-contraction (E-C) coupling; tune cardiac excitability; and regulate gene expression. In ventricular myocytes, Ca1.2 channels are predominantly located in t-tubules where they are in proximity to ryanodine receptors to trigger cardiac E-C coupling. A subset of ventricular Ca1.2 channels existing on the surface sarcolemma, including in caveolae, have less well-defined functions. Cardiac Ca1.2 channels are famously up-regulated by protein kinase A as a component of the 'fight-or-flight' response. The molecular details of how this kinase regulates cardiac Ca1.2 channels are controversial and under intensive study. Here, we critically review recent work addressing the putative functions of microdomain cardiac Ca1.2 channels, and their regulation by distinct kinases in health and disease.