Cell surface beta-1,4-galactosyltransferase-I activates G protein-dependent exocytotic signaling

ZP3 is a protein in the mammalian egg coat (zona pellucida) that binds sperm and stimulates acrosomal exocytosis, enabling sperm to penetrate the zona pellucida. The nature of the ZP3 receptor/s on sperm is a matter of considerable debate, but most evidence suggests that ZP3 binds to beta-1,4-galactosyltransferase-I (GalTase) on the sperm surface. It has been suggested that ZP3 induces the acrosome reaction by crosslinking GalTase, activating a heterotrimeric G protein. In this regard, acrosomal exocytosis is sensitive to pertussis toxin and the GalTase cytoplasmic domain can precipitate G(i) from sperm lysates. Sperm from mice that overexpress GalTase bind more soluble ZP3 and show accelerated G protein activation, whereas sperm from mice with a targeted deletion in GalTase have markedly less ability to bind soluble ZP3, undergo the ZP3-induced acrosome reaction, and penetrate the zona pellucida. We have examined the ability of GalTase to function as a ZP3 receptor and to activate heterotrimeric G proteins using Xenopus laevis oocytes as a heterologous expression system. Oocytes that express GalTase bound ZP3 but did not bind other zona pellucida glycoproteins. After oocyte maturation, ZP3 or GalTase antibodies were able to trigger cortical granule exocytosis and activation of GalTase-expressing eggs. Pertussis toxin inhibited GalTase-induced egg activation. Consistent with G protein activation, both ZP3 and anti-GalTase antibodies increased GTP-gamma[(35)S] binding as well as GTPase activity in membranes from eggs expressing GalTase. Finally, mutagenesis of a putative G protein activation motif within the GalTase cytoplasmic domain eliminated G protein activation in response to ZP3 or anti-GalTase antibodies. These results demonstrate directly that GalTase functions as a ZP3 receptor and following aggregation, is capable of activating pertussis toxin-sensitive G proteins leading to exocytosis.     

Quality of Life,Safety and Efficacy Profile of Thermostable Flolan in Pulmonary Arterial Hypertension

Background

Flolan (epoprostenol sodium) is most commonly prescribed to patients with severe pulmonary arterial hypertension (PAH) owing to the requirement that the drug be delivered by continuous intravenous infusion and the reconstituted solution may only be administered up to 24 hours when it is maintained between a temperature of 2°C and 8°C. The aim of this single-arm, open label study was to describe the effects of the new thermostable formulation of Flolan on health-related quality of life (HRQoL) and ease of administration in subjects switching from the currently marketed Flolan to the reformulated product.

Methods

Following a 4-week run-in period and after 4 weeks of treatment with the reformulated product, patients completed the SF-36 HRQoL questionnaire and a study-specific questionnaire evaluating ease of administration, along with World Health Organization (WHO) functional class, six-minute walked distance (6MWD) and N-terminal-pro B-type natriuretic peptide (NT-proBNP) assessment.

Results

16 participants completed the study. The SF-36 scores remained unchanged from baseline to Week 4. Conversely, there were small improvements for the majority of the study-specific questionnaire items and 14 (88%) subjects preferred the reformulated product to the currently marketed Flolan. There was no significant change in the dose of reformulated product, 6MWD, Borg dyspnoea index, WHO functional class and mean NT-proBNP levels. No significant changes in haemodynamic parameters were seen from baseline to 2 hours post transition in a subset of patients undergoing catheterization.

Conclusion

The reformulated product was not associated with significant improvement in HRQoL compared with the currently marketed Flolan as measured by the SF-36. However, most subjects preferred the reformulated product to the currently marketed Flolan. Moreover, the 2 formulations of Flolan had similar safety and efficacy profiles.

Trial Registration

ClinicalTrials.gov {"type":"clinical-trial","attrs":{"text":"NCT01462565","term_id":"NCT01462565"}}NCT01462565