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

Hao Jiang,Wenwen Wang,Yin Zhang,William W Yao,Jiying Jiang,Bo Qin,Wendy Y Yao,Fusheng Liu,Huihui Wu,Tarsha L Ward,Chun Wei Chen,Lifang Liu,Xia Ding,Xing Liu,Xuebiao Yao

doi:10.1074/jbc.m115.668855

Abstract

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.

Highlights

Polarized acid secretion in gastric parietal cells requires ezrin and its phosphorylation at Ser-66 by cAMP-dependent protein kinase (PKA)
Dynamic Phosphorylation of Ezrin during Parietal Cell Activation of Acid Secretion—Our early study showed that histamine stimulation of parietal cell acid secretion results in ezrin phosphorylation at Ser-66, which is sensitive to the PKA inhibitor H89, suggesting that phosphorylation of ezrin is a downstream event of PKA activity [3]
Ser-66 of ezrin was characterized as a substrate of PKA [13], which is essential for parietal cell activation via interacting with syntaxin 3 for tubulovesicle docking [19]

Summary

Introduction

Polarized acid secretion in gastric parietal cells requires ezrin and its phosphorylation at Ser-66 by cAMP-dependent protein kinase (PKA). Results: Phosphorylation of Ser-66 induces an ezrin conformational change that promotes the phosphorylation of Thr-567 by MST4. Conclusion: PKA phosphorylates MST4 and ezrin to orchestrate histamine-elicited acid secretion. Significance: The PKA-MST4-ezrin signaling axis is essential for parietal cell activation. Acid secretion into the lumen is triggered by activation of the PKA cascade, which 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. 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 promotes MST4 kinase activity. 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 hista-

Methods

Results

Conclusion