Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ezrin-radixin-moesin proteins provide a regulated linkage between membrane proteins and the cortical cytoskeleton and also participate in signal transduction pathways. Ezrin is localized to the apical membrane of parietal cells and couples the protein kinase A activation cascade to the regulated HCl secretion. Our recent proteomic study revealed a protein complex of ezrin-ACAP4-ARF6 essential for volatile membrane remodeling (Fang, Z., Miao, Y., Ding, X., Deng, H., Liu, S., Wang, F., Zhou, R., Watson, C., Fu, C., Hu, Q., Lillard, J. W., Jr., Powell, M., Chen, Y., Forte, J. G., and Yao, X. (2006) Mol. Cell Proteomics 5, 1437-1449). However, knowledge of whether ACAP4 physically interacts with ezrin and how their interaction is integrated into membrane-cytoskeletal remodeling has remained elusive. Here we provide the first evidence that ezrin interacts with ACAP4 in a protein kinase A-mediated phosphorylation-dependent manner through the N-terminal 400 amino acids of ACAP4. ACAP4 locates in the cytoplasmic membrane in resting parietal cells but translocates to the apical plasma membrane upon histamine stimulation. ACAP4 was precipitated with ezrin from secreting but not resting parietal cell lysates, suggesting a phospho-regulated interaction. Indeed, this interaction is abolished by phosphatase treatment and validated by an in vitro reconstitution assay using phospho-mimicking ezrin(S66D). Importantly, ezrin specifies the apical distribution of ACAP4 in secreting parietal cells because either suppression of ezrin or overexpression of non-phosphorylatable ezrin prevents the apical localization of ACAP4. In addition, overexpressing GTPase-activating protein-deficient ACAP4 results in an inhibition of apical membrane-cytoskeletal remodeling and gastric acid secretion. Taken together, these results define a novel molecular mechanism linking ACAP4-ezrin interaction to polarized epithelial secretion.
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PMID:Phospho-regulated ACAP4-Ezrin interaction is essential for histamine-stimulated parietal cell secretion. 2036 10

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.
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PMID:MST4 kinase phosphorylates ACAP4 protein to orchestrate apical membrane remodeling during gastric acid secretion. 2880 54