A Kinetic Map of the Homomeric Voltage-Gated Potassium Channel (Kv) Family.

The voltage-gated potassium (Kv) channels, encoded by 40 genes, repolarize all electrically excitable cells, including plant, cardiac, and neuronal cells. Although these genes were fully sequenced decades ago, a comprehensive kinetic characterization of all Kv channels is still missing, especially near physiological temperature. Here, we present a standardized kinetic map of the 40 homomeric Kv channels systematically characterized at 15, 25, and 35°C. Importantly, the Kv kinetics at 35°C differ significantly from commonly reported kinetics, usually performed at room temperature. We observed voltage-dependent Q10 for all active Kv channels and inherent heterogeneity in kinetics for some of them. Kinetic properties are consistent across different host cell lines and conserved across mouse, rat, and human. All electrophysiology data from all Kv channels are made available through a public website (Channelpedia). This dataset provides a solid foundation for exploring kinetics of heteromeric channels, roles of auxiliary subunits, kinetic modulation, and for building accurate Kv models.

Cell-permeable peptides induce dose- and length-dependent cytotoxic effects.

We have explored the threshold of tolerance of three unrelated cell types to treatments with potential cytoprotective peptides bound to Tat(48-57) and Antp(43-58) cell-permeable peptide carriers. Both Tat(48-57) and Antp(43-58) are well known for their good efficacy at crossing membranes of different cell types, their overall low toxicity, and their absence of leakage once internalised. Here, we show that concentrations of up to 100 microM of Tat(48-57) were essentially harmless in all cells tested, whereas Antp(43-58) was significantly more toxic. Moreover, all peptides bound to Tat(48-57) and Antp(43-58) triggered significant and length-dependent cytotoxicity when used at concentrations above 10 microM in all but one cell types (208F rat fibroblasts), irrespective of the sequence of the cargo. Absence of cytotoxicity in 208F fibroblasts correlated with poor intracellular peptide uptake, as monitored by confocal laser scanning fluorescence microscopy. Our data further suggest that the onset of cytotoxicity correlates with the activation of two intracellular stress signalling pathways, namely those involving JNK, and to a lesser extent p38 mitogen-activated protein kinases. These responses are of particular concern for cells that are especially sensitive to the activation of stress kinases. Collectively, these results indicate that in order to avoid unwanted and unspecific cytotoxicity, effector molecules bound to Tat(48-57) should be designed with the shortest possible sequence and the highest possible affinity for their binding partners or targets, so that concentrations below 10 microM can be successfully applied to cells without harm. Considering that cytotoxicity associated to Tat(48-57)- and Antp(43-58) bound peptide conjugates was not restricted to a particular type of cells, our data provide a general framework for the design of cell-penetrating peptides that may apply to broader uses of intracellular peptide and drug delivery.

Risk prediction of developing venous thrombosis in combined oral contraceptive users.

BACKGROUND: Venous thromboembolism (VTE) is a complex multifactorial disease influenced by genetic and environmental risk factors. An example for the latter is the regular use of combined oral contraceptives (CC), which increases the risk to develop VTE by 3 to 7 fold, depending on estrogen dosage and the type of progestin present in the pill. One out of 1'000 women using CC develops thrombosis, often with life-long consequences; a risk assessment is therefore necessary prior to such treatment. Currently known clinical risk factors associated with VTE development in general are routinely checked by medical doctors, however they are far from being sufficient for risk prediction, even when combined with genetic tests for Factor V Leiden and Factor II G20210A variants. Thus, clinical and notably genetic risk factors specific to the development of thrombosis associated with the use of CC in particular should be identified. METHODS AND FINDINGS: Step-wise (logistic) model selection was applied to a population of 1622 women using CC, half of whom (794) had developed a thromboembolic event while using contraceptives. 46 polymorphisms and clinical parameters were tested in the model selection and a specific combination of 4 clinical risk factors and 9 polymorphisms were identified. Among the 9 polymorphisms, there are two novel genetic polymorphisms (rs1799853 and rs4379368) that had not been previously associated with the development of thromboembolic event. This new prediction model outperforms (AUC 0.71, 95% CI 0.69-0.74) previously published models for general thromboembolic events in a cross-validation setting. Further validation in independent populations should be envisaged. CONCLUSION: We identified two new genetic variants associated to VTE development, as well as a robust prediction model to assess the risk of thrombosis for women using combined oral contraceptives. This model outperforms current medical practice as well as previously published models and is the first model specific to CC use.

Induction of apoptosis in human corneal and HeLa cells by mutated BIGH3.

PURPOSE: To determine the effects of overexpression of mutated BIGH3 in HeLa and human corneal epithelial (HCE) cells. METHODS: Six mutations known to be responsible for autosomal dominant corneal dystrophies linked to chromosome 5 were generated in a BIGH3 expression vector and transfected in HeLa and HCE cells. The expression and secretion of the various BIGH3-EGFP fusion proteins were measured by Western blot analysis. Apoptotic cells were identified by Hoechst/propidium iodide and annexin V staining. Lactate dehydrogenase (LDH) activity was measured in the medium of transfected cells. Truncated BIGH3 protein and site-specific mutations were generated to determine the exact region that mediated apoptosis. RESULT: The overexpressed BIGH3 fusion protein was secreted regardless of its mutation status and was clearly observed in the culture medium. Overexpression of mutated BIGH3 induced apoptosis in both cell lines through activation of caspase-3. Although all the disease-causing mutations tested in this experiment induced apoptosis, the strongest effect was observed with the R124C and R555W mutations. Overexpression of a carboxyl-truncated BIGH3 protein did not induce apoptosis, suggesting that a region located in the C-terminal domain was necessary to mediate cell death. In addition, mutation of the Pro-Asp-Ile (PDI) site at 616-618 was sufficient to prevent induction of apoptosis. CONCLUSIONS: Overexpression of mutated BIGH3 induces apoptosis in HeLa and HCE cells through activation of a pathway that uses the PDI domain of the fourth internal Fas domain and activation of caspase-3. Because DI is a known site of interaction with alpha 3 beta 1 integrins, it suggests that integrins play a role in mediating apoptosis in the system used in the current study. This work suggests that apoptosis is a key element in the pathophysiology of BIGH3-related corneal dystrophies.