The endosomal trafficking regulator LITAF controls the cardiac Nav1.5 channel via the ubiquitin ligase NEDD4-2

The QT interval is a recording of cardiac electrical activity. Previous genome-wide association studies identified genetic variants that modify the QT interval upstream of LITAF (lipopolysaccharide-induced tumor necrosis factor-α factor), a protein encoding a regulator of endosomal trafficking. However, it was not clear how LITAF might impact cardiac excitation. We investigated the effect of LITAF on the voltage-gated sodium channel Nav1.5, which is critical for cardiac depolarization. We show that overexpressed LITAF resulted in a significant increase in the density of Nav1.5-generated voltage-gated sodium current I_Na and Nav1.5 surface protein levels in rabbit cardiomyocytes and in HEK cells stably expressing Nav1.5. Proximity ligation assays showed co-localization of endogenous LITAF and Nav1.5 in cardiomyocytes, whereas co-immunoprecipitations confirmed they are in the same complex when overexpressed in HEK cells. In vitro data suggest that LITAF interacts with the ubiquitin ligase NEDD4-2, a regulator of Nav1.5. LITAF overexpression down-regulated NEDD4-2 in cardiomyocytes and HEK cells. In HEK cells, LITAF increased ubiquitination and proteasomal degradation of co-expressed NEDD4-2 and significantly blunted the negative effect of NEDD4-2 on I_Na. We conclude that LITAF controls cardiac excitability by promoting degradation of NEDD4-2, which is essential for removal of surface Nav1.5. LITAF-knockout zebrafish showed increased variation in and a nonsignificant 15% prolongation of action potential duration. Computer simulations using a rabbit-cardiomyocyte model demonstrated that changes in Ca²⁺ and Na⁺ homeostasis are responsible for the surprisingly modest action potential duration shortening. These computational data thus corroborate findings from several genome-wide association studies that associated LITAF with QT interval variation.     

AUXIN RESPONSE FACTOR 2 Intersects Hormonal Signals in the Regulation of Tomato Fruit Ripening

The involvement of ethylene in fruit ripening is well documented, though knowledge regarding the crosstalk between ethylene and other hormones in ripening is lacking. We discovered that AUXIN RESPONSE FACTOR 2A (ARF2A), a recognized auxin signaling component, functions in the control of ripening. ARF2A expression is ripening regulated and reduced in the rin, nor and nr ripening mutants. It is also responsive to exogenous application of ethylene, auxin and abscisic acid (ABA). Over-expressing ARF2A in tomato resulted in blotchy ripening in which certain fruit regions turn red and possess accelerated ripening. ARF2A over-expressing fruit displayed early ethylene emission and ethylene signaling inhibition delayed their ripening phenotype, suggesting ethylene dependency. Both green and red fruit regions showed the induction of ethylene signaling components and master regulators of ripening. Comprehensive hormone profiling revealed that altered ARF2A expression in fruit significantly modified abscisates, cytokinins and salicylic acid while gibberellic acid and auxin metabolites were unaffected. Silencing of ARF2A further validated these observations as reducing ARF2A expression let to retarded fruit ripening, parthenocarpy and a disturbed hormonal profile. Finally, we show that ARF2A both homodimerizes and interacts with the ABA STRESS RIPENING (ASR1) protein, suggesting that ASR1 might be linking ABA and ethylene-dependent ripening. These results revealed that ARF2A interconnects signals of ethylene and additional hormones to co-ordinate the capacity of fruit tissue to initiate the complex ripening process.     

A Pan-ALDH1A Inhibitor Induces Necroptosis in Ovarian Cancer Stem-like Cells

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Ile-177 and Ser-180 in the S1 segment are critically important in Kv1.1 channel function

Ile-177 and Ser-180 are conserved residues in the first transmembrane segment (S1) of the Shaker, Shab, Shaw, and Shal subfamilies of voltage-gated K+ channels. Here we report that the mutation of these residues in Kv1.1 to leucine, proline, or arginine abolished the expression of outward potassium currents in Xenopus oocytes. Co-injection of these mutant cRNAs and wild type Kv1.1 cRNA into Xenopus oocytes exerted a potent dominant negative effect resulting in the suppression of Kv1.1-encoded currents. Transient transfection experiments of COS-7 cells revealed that the S1 mutants directed the synthesis of Kv1.1 polypeptides. Quantitative co-immunoprecipitation assays revealed that most of the S1 mutants co-assembled and formed both homo- and heteromultimeric complexes. Furthermore, the mutated polypeptides could reach the plasma membranes of transfected Sol8 cells. We conclude that mutations of Ile-177 and Ser-180 do not interfere with either the assembly of multimeric channel complexes or the targeting of these complexes to the plasma membrane. It is likely that these residues are involved in helix-helix interactions that are critical to the proper functioning of voltage-gated potassium channels.     

In vitro amplification of protease-resistant prion protein requires free sulfhydryl groups

Prions, the infectious agents of transmissible spongiform encephalopathies, are composed primarily of a misfolded protein designated PrP(Sc). Prion-infected neurons generate PrP(Sc) from a host glycoprotein designated PrP(C) through a process of induced conformational change, but the molecular mechanism by which PrP(C) undergoes conformational change into PrP(Sc) remains unknown. We employed an in vitro PrP(Sc) amplification technique adapted from protein misfolding cyclic amplification (PMCA) to investigate the mechanism of prion-induced protein conformational change. Using this technique, PrP(Sc) from diluted scrapie-infected brain homogenate can be amplified >10-fold without sonication when mixed with normal brain homogenate under nondenaturing conditions. PrP(Sc) amplification in vitro exhibits species and strain specificity, depends on both time and temperature, only requires membrane-bound components, and does not require divalent cations. In vitro amplification of Syrian hamster Sc237 PrP(Sc) displays an optimum pH of approximately 7, whereas amplification of CD-1 mouse RML PrP(Sc) is optimized at pH approximately 6. The thiolate-specific alkylating agent N-ethylmaleimide (NEM) as well as the reversible thiol-specific blockers p-hydroxymercuribenzoic acid (PHMB) and mersalyl acid inhibited PrP(Sc) amplification in vitro, indicating that the conformational change from PrP(C) to PrP(Sc) requires a thiol-containing factor. Our data provide the first evidence that a reactive chemical group plays an essential role in the conformational change from PrP(C) to PrP(Sc).     

Pregnancy outcome post renal transplantation

BACKGROUND: The success in performing organ transplantations and prevention of rejection has resulted not only in a substantial increase in life expectancy, but also improvement in the patients' quality of life. Thus, women who underwent organ transplantation are now reaching puberty and the age of reproduction. This has presented new challenges regarding the teratogenicity and the long-term effect of immunosuppressive medications used by these patients. Previous studies have shown that pregnancies after renal transplantation are associated with an increased risk for both the mother and the fetus. There is, however, very little information available on neonatal and long-term pediatric follow-up of babies born to mothers who have undergone renal transplantation and have been exposed to immunosuppressive medications, compared to controls. We report the experience of our center, the largest in Canada, regarding the prenatal and long-term postnatal outcome of pregnancies after renal transplantation. METHODS: This is a retrospective case series reporting the outcome of 44 consecutive pregnancies followed by the Toronto Renal Transplant Program. Follow-up data were gathered on the 32 live born children by either a return visit to the clinic or by telephone interview. Medical, as well as developmental information, was gathered on all children and the study group was compared to controls, matched for maternal age (+/-2 years) and smoking status, obtained through the Motherisk Program. RESULTS: Of the 44 pregnancies followed by us, there were 32 live-born children delivered by 26 mothers and 12 stillborn/abortuses. Twenty-six pregnancies were treated with cyclosporine, azathioprine and prednisone, 13 with azathioprine and prednisone and five with cyclosporine and prednisone. The mean gestational age at delivery in the study group was 36.5 +/- 2.7 weeks compared to 40.2 +/- 1.6 weeks in the control group (P < 0.001). The mean birthweight in the study group was 2.54 +/- 0.67 kg, compared to 3.59 +/- 0.53 kg in the control group (P < 0.0001). In the study group there was one child with multiple anomalies and four stillbirths compared to zero in the control group. There were also six spontaneous abortions and two therapeutic abortions in the study group. On follow-up (from 3 months to 11 years of age) there was one child with insulin-dependent diabetes mellitus, two children with asthma and one child with recurrent otitis media. Developmental follow-up revealed one child with moderate to severe sensorineural hearing loss, one child with a learning disability and one child with pervasive developmental disorder. In none of these cases were there signs of perinatal asphyxia. CONCLUSION: There are significantly more stillbirths, preterm deliveries and increased incidence of low birth weight in the transplant group. Most pregnancies in the study group went well, however, and their offspring had normal postnatal growth and development. Further studies with long-term pediatric follow-up are needed to delineate their outcome and rule out possible long term effects of the immunosuppressive medication on their growth, development, reproduction and general health.