Proactive functional classification of all possible missense single-nucleotide variants in KCNQ4.

Clinical exome sequencing has yielded extensive disease-related missense single-nucleotide variants (SNVs) of uncertain significance, leading to diagnostic uncertainty. KCNQ4 is one of the most commonly responsible genes for autosomal dominant nonsyndromic hearing loss. According to the gnomAD cohort, approximately one in 100 people harbors missense variants in KCNQ4 (missense variants with minor allele frequency > 0.1% were excluded), but most are of unknown consequence. To prospectively characterize the function of all 4085 possible missense SNVs of human KCNQ4, we recorded the whole-cell currents using the patch-clamp technique and categorized 1068 missense SNVs as loss of function, as well as 728 loss-of-function SNVs located in the transmembrane domains. Further, to mimic the heterozygous condition in Deafness nonsyndromic autosomal dominant 2 (DFNA2) patients caused by KCNQ4 variants, we coexpressed loss-of-function variants with wild-type KCNQ4 and found 516 variants showed impaired or only partially rescued heterogeneous channel function. Overall, our functional classification is highly concordant with the auditory phenotypes in Kcnq4 mutant mice and the assessments of pathogenicity in clinical variant interpretations. Taken together, our results provide strong functional evidence to support the pathogenicity classification of newly discovered KCNQ4 missense variants in clinical genetic testing.

The S2-S3 Loop of Kv7.4 Channels Is Essential for Calmodulin Regulation of Channel Activation.

Kv7.4 (KCNQ4) voltage-gated potassium channels control excitability in the inner ear and the central auditory pathway. Mutations in Kv7.4 channels result in inherited progressive deafness in humans. Calmodulin (CaM) is crucial for regulating Kv7 channels, but how CaM affects Kv7 activity has remained unclear. Here, based on electrophysiological recordings, we report that the third EF hand (EF3) of CaM controls the calcium-dependent regulation of Kv7.4 activation and that the S2-S3 loop of Kv7.4 is essential for the regulation mediated by CaM. Overexpression of the mutant CaM1234, which loses the calcium binding ability of all four EF hands, facilitates Kv7.4 activation by accelerating activation kinetics and shifting the voltage dependence of activation leftwards. The single mutant CaM3, which loses the calcium binding ability of the EF3, phenocopies facilitating effects of CaM1234 on Kv7.4 activation. Kv7.4 channels co-expressed with wild-type (WT) CaM show inhibited activation when intracellular calcium levels increase, while Kv7.4 channels co-expressed with CaM1234 or CaM3 are insensitive to calcium. Mutations C156A, C157A, C158V, R159, and R161A, which are located within the Kv7.4 S2-S3 loop, dramatically facilitate activation of Kv7.4 channels co-expressed with WT CaM but have no effect on activation of Kv7.4 channels co-expressed with CaM3, indicating that these five mutations decrease the inhibitory effect of Ca2+/CaM. The double mutation C156A/R159A decreases Ca2+/CaM binding and completely abolishes CaM-mediated calcium-dependent regulation of Kv7.4 activation. Taken together, our results provide mechanistic insights into CaM regulation of Kv7.4 activation and highlight the crucial role of the Kv7.4 S2-S3 loop in CaM regulation.

Aspirin inhibits growth of ovarian cancer by upregulating caspase-3 and downregulating bcl-2.

[This retracts the article DOI: 10.3892/ol.2016.4607.].

ATP-dependent modulation of MgtE in Mg2+ homeostasis.

Magnesium is an essential ion for numerous physiological processes. MgtE is a Mg2+ selective channel involved in the maintenance of intracellular Mg2+ homeostasis, whose gating is regulated by intracellular Mg2+ levels. Here, we report that ATP binds to MgtE, regulating its Mg2+-dependent gating. Crystal structures of MgtE-ATP complex show that ATP binds to the intracellular CBS domain of MgtE. Functional studies support that ATP binding to MgtE enhances the intracellular domain affinity for Mg2+ within physiological concentrations of this divalent cation, enabling MgtE to function as an in vivo Mg2+ sensor. ATP dissociation from MgtE upregulates Mg2+ influx at both high and low intracellular Mg2+ concentrations. Using site-directed mutagenesis and structure based-electrophysiological and biochemical analyses, we identify key residues and main structural changes involved in the process. This work provides the molecular basis of ATP-dependent modulation of MgtE in Mg2+ homeostasis.MgtE is an Mg2+ transporter involved in Mg2+ homeostasis. Here, the authors report that ATP regulates the Mg+2-dependent gating of MgtE and use X-ray crystallography combined with functional studies to propose the molecular mechanisms involved in this process.

Aspirin inhibits growth of ovarian cancer by upregulating caspase-3 and downregulating bcl-2.

The aim of the present study was to investigate the effect and mechanism of different concentrations of aspirin in inhibiting the ovarian cancer of p53N236S gene knock-in mice. In total, 28 male p53S mice, with an age range of 4-6 weeks and weight of 20-25 g were selected. The animals were transplanted with SKOV3 cells to establish subdermal human ovarian cancer. The mice were randomly divided into different groups according to the aspirin concentrations (mmol/l) used, i.e., 0, 1, 2 and 3. Subsequently, intraperitoneal injection was performed once every two days for 3 weeks. The tumor volume, lifetime, tumor cell proliferation inhibition rates, caspase-3 protein and bcl-2 protein expression of the four groups were analyzed and compared. Following aspirin treatment for 1, 2 and 3 weeks, the tumor volume of the 3 mmol/l aspirin group was significantly smaller than the other groups (P<0.05). The higher concentration of aspirin led to a smaller tumor size (P<0.05). The cell proliferation inhibition rate of the 3 mmol/l aspirin group was significantly larger than that of other groups (P<0.05). The relative expression level of caspase-3, bcl-2 protein of the 3 mmol/l aspirin group was significantly improved and reduced, respectively. In conclusion, aspirin can inhibit the growth of ovarian cancer of p53S rats due to its upregulation of the expression of caspase-3 protein and downregulation of the expression of bcl-2 protein.