Coupling of endothelin receptors to the ERK/MAP kinase pathway. Roles of palmitoylation and G(alpha)q

Endothelins are potent mitogens that stimulate extracellular signal-regulated kinases (ERK/MAP kinases) through their cognate G-protein-coupled receptors, ET(A) and ET(B). To address the role of post-translational ET receptor modifications such as acylation on ERK activation and to identify relevant downstream effectors coupling the ET receptor to the ERK signaling cascades we have constructed a panel of palmitoylation-deficient ET receptor mutants with differential G(alpha) protein binding capacity. Endothelin-1 stimulation of wild-type ET(A) or ET(B) induced a fivefold to sixfold increase in ERK in COS-7 and CHO cells whereas full-length nonpalmitoylated ET(A) and ET(B) mutants failed to stimulate ERK. A truncated ET(B) lacking the C-terminal tail domain including putative phosphorylation and arrestin binding site(s) but retaining the critical palmitoylation site(s) was still able to fully stimulate ERK activation. Using mutated ET receptors with selective G-protein-coupling we found that endothelin-induced stimulation of G(alpha)q, but not of G(alpha)i or G(alpha)s, is essential for endothelin-mediated ERK activation. Inhibition of protein kinases A and C or epidermal growth factor receptor kinase failed to prevent ET(A)- and ET(B)-mediated ERK activation whereas blockage of phospholipase C-beta completely abrogated endothelin-promoted ERK activation through ET(A) and ET(B) in recombinant COS-7 and native C6 cells. Complex formation of Ca2+ or inhibition of Src family tyrosine kinases prevented ET-1-induced ERK-2 activation in C6-cells. Our results indicate that endothelin-promoted ERK/MAPK activation criticially depends on palmitoylation but not on phosphorylation of ET receptors, and that the G(alpha)q/phospholipase C-beta/Ca2+/Src signaling cascade is necessary for efficient coupling of ET receptors to the ERK/MAPK pathway.

Durable protein lattices of clathrin that can be functionalized with nanoparticles and active biomolecules

Biological molecules that self-assemble and interact with other molecules are attractive building blocks for engineering biological devices. DNA has been widely used for the creation of nanomaterials, but the use of proteins remains largely unexplored. Here, we show that clathrin can form homogeneous and extended two-dimensional lattices on a variety of substrates, including glass, metal, carbon and plastic. Clathrin is a three-legged protein complex with unique self-assembling properties and is relevant in the formation of membrane transport vesicles in eukaryotic cells. We used a fragment of the adaptor protein epsin to immobilize clathrin lattices on the substrates. The lattices span multiple square millimetres with a regular periodicity of 30 nm and can be functionalized via modified subunits of clathrin with either inorganic nanoparticles or active enzymes. The lattices can be stored for months after crosslinking and stabilization with uranyl acetate. They could be dehydrated and rehydrated without loss of function, offering potential applications in sensing and as biosynthetic reactors.

Efficacy of four different left atrial appendage closure techniques during cardiac surgery-A transesophageal echocardiography follow-up study

Objective

Closure of the left atrial appendage (LAA) is a routine part of atrial fibrillation ablation surgery and significantly reduces stroke rates. Different LAA-closure techniques are used in cardiac surgery with variable results reported. We therefore evaluated the efficacy of 4 different LAA-closure techniques in patients undergoing cardiac surgery.

Methods

In total, 149 patients who underwent concomitant LAA closure during cardiac surgery between 2015 and 2019 were included in this retrospective transesophageal echocardiography study. Four different LAA-closure techniques were evaluated: LAA clipping (n = 62), suture ligation (n = 28), stapler resection (n = 30), and surgical LAA excision (n = 29). Successful LAA closure was defined as absence of LAA perfusion and absence of a stump greater than 10 mm.

Results

The mean patients age was 68.7 ± 9.4 years; 61.7% were male. No complications related to LAA closure were observed. Mean follow-up was 36.5 ± 8 months. Transesophageal echocardiography follow-up showed the following LAA closure success rates: LAA clip 98.4%, surgical excision 93.1%, stapler resection 76.6%, and suture ligation 39.2%. Suture ligation resulted in a high rate of recanalization (50%) and residual stumps (10.8%), whereas stapler resection resulted in a high rate of residual stumps (23.4%). Overall, 4 patients (2.7%) had a stroke during follow-up. In detail, 2 of 27 (7.4%) patients with unsuccessful LAA closure had a stroke, whereas 2 of the 122 (1.6%) patients with successful LAA closure had a stroke.

Conclusions

In our study, LAA clipping and surgical LAA excision proved to be both successful LAA-closure methods. External LAA ligation and stapler resection resulted in low rates of successful LAA closure and should be avoided.