MST4 kinase phosphorylates ACAP4 protein to orchestrate apical membrane remodeling during gastric acid secretion.

Digestion in the stomach depends on acidification of the lumen. Histamine-elicited acid secretion is triggered by activation of the PKA cascade, which ultimately results in the insertion of gastric H,K-ATPases into the apical plasma membranes of parietal cells. Our recent study revealed the functional role of PKA-MST4-ezrin signaling axis in histamine-elicited acid secretion. However, it remains uncharacterized how the PKA-MST4-ezrin signaling axis operates the insertion of H,K-ATPases into the apical plasma membranes of gastric parietal cells. Here we show that MST4 phosphorylates ACAP4, an ARF6 GTPase-activating protein, at Thr545 Histamine stimulation activates MST4 and promotes MST4 interaction with ACAP4. ACAP4 physically interacts with MST4 and is a cognate substrate of MST4 during parietal cell activation. The phosphorylation site of ACAP4 by MST4 was mapped to Thr545 by mass spectrometric analyses. Importantly, phosphorylation of Thr545 is essential for acid secretion in parietal cells because either suppression of ACAP4 or overexpression of non-phosphorylatable ACAP4 prevents the apical membrane reorganization and proton pump translocation elicited by histamine stimulation. In addition, persistent overexpression of MST4 phosphorylation-deficient ACAP4 results in inhibition of gastric acid secretion and blockage of tubulovesicle fusion to the apical membranes. Significantly, phosphorylation of Thr545 enables ACAP4 to interact with ezrin. Given the location of Thr545 between the GTPase-activating protein domain and the first ankyrin repeat, we reason that MST4 phosphorylation elicits a conformational change that enables ezrin-ACAP4 interaction. Taken together, these results define a novel molecular mechanism linking the PKA-MST4-ACAP4 signaling cascade to polarized acid secretion in gastric parietal cells.

Cell Polarity Kinase MST4 Cooperates with cAMP-dependent Kinase to Orchestrate Histamine-stimulated Acid Secretion in Gastric Parietal Cells.

The digestive function of the stomach depends on acidification of the gastric lumen. Acid secretion into the lumen is triggered by activation of the PKA cascade, which ultimately results in the insertion of gastric H,K-ATPases into the apical plasma membranes of parietal cells. A coupling protein is ezrin, whose phosphorylation at Ser-66 by PKA is required for parietal cell activation. However, little is known regarding the molecular mechanism(s) by which this signaling pathway operates in gastric acid secretion. Here we show that PKA cooperates with MST4 to orchestrate histamine-elicited acid secretion by phosphorylating ezrin at Ser-66 and Thr-567. Histamine stimulation activates PKA, which phosphorylates MST4 at Thr-178 and then promotes MST4 kinase activity. Interestingly, activated MST4 then phosphorylates ezrin prephosphorylated by PKA. Importantly, MST4 is important for acid secretion in parietal cells because either suppression of MST4 or overexpression of non-phosphorylatable MST4 prevents the apical membrane reorganization and proton pump translocation elicited by histamine stimulation. In addition, overexpressing MST4 phosphorylation-deficient ezrin results in an inhibition of gastric acid secretion. Taken together, these results define a novel molecular mechanism linking the PKA-MST4-ezrin signaling cascade to polarized epithelial secretion in gastric parietal cells.

Accuracy of antibacterial indication documentation in an electronic medicines management system.

Introduction: Electronic medicines management (EMM) systems are relatively new in the Australian healthcare system. This tertiary hospital network implemented an EMM in 2018, with mandatory documentation of antimicrobial indication when prescribing. Free-text (unrestricted) and pre-defined dropdown (restricted) indications are utilized according to antimicrobial restriction. Objectives: To determine accuracy of antibacterial indication documentation on the medication administration record (MAR) when prescribing and to evaluate factors influencing accuracy of documentation. Methods: A random sample of 400 inpatient admissions of ≥24 h, between March and September 2019, with the first antibacterial prescription per encounter reviewed retrospectively. Demographic and prescription details were extracted. Indication accuracy was assessed by comparing MAR documentation with the medical notes (gold standard). Statistical analysis compared factors associated with accuracy of indication using chi-squared and Fisher's exact tests. Results: Antibacterials were prescribed in 9708 admissions. Of the 400 patients included (60% male; median age 60 years, IQR 40-73), 225 prescriptions were unrestricted and 175 were restricted. Patients were managed by emergency (118), surgical (178) and medical (104) teams. Overall accuracy of antibacterial indication documentation on the MAR was 86%. A higher accuracy rate was found for the unrestricted proportion compared with the restricted proportion (94.2% versus 75.2%; P < 0.0001). Surgical teams had higher accuracy compared with medical and emergency teams (94.4% versus 78.8% versus 79.7%; P < 0.0001). Discussion: Antibacterial indication documentation on the MAR when prescribing demonstrated a high rate of accuracy. Multiple factors influenced this accuracy, which requires further study to determine the impact on accuracy, with a view to improve future EMM builds.

A Video-Based Reflective Design to Prepare First Year Pharmacy Students for Their First Objective Structured Clinical Examination (OSCE).

We explored the use of a video-based reflective design in preparing first-year pharmacy students for their Objective Structured Clinical Examination (OSCE) in Victoria, Australia. This involved pre-workshop activities (a recording of themselves simulating the pharmacist responding to a simple primary care problem, written reflection, review of the OSCE video examples and pre-workshop survey); workshop activities (peer feedback on videos) and post-workshop activities (summative MCQ quiz and post-workshop survey). These activities took place three weeks before their OSCE. A mixed-method study design was employed with quantitative and qualitative analyses of the surveys and a focus group. A total of 137 students (77.4%) completed the pre- and post-workshop surveys, and ten students participated in the focus group. More student participants (54%) reported feeling prepared for the OSCE post-workshop than pre-workshop (13%). The majority (92%) agreed that filming, watching and reflecting on their video allowed them to learn and improve on their skills for the OSCE. The regression analysis found that video recording submissions and written reflections correlated positively with student OSCE performances, and the video-based reflective design learning experience was perceived to be beneficial in multiple ways. Thematic analysis of the focus group data revealed that students acquired metacognitive skills through the self-assessment of their video recordings, developed an awareness of their learning and were able to identify learning strategies to prepare for their first OSCE. Fostering students' feedback literacy could be considered in future educational designs.