A1 adenosine receptor-stimulated exocytosis in bladder umbrella cells requires phosphorylation of ADAM17 Ser-811 and EGF receptor transactivation.
Bottom Line: Despite the importance of ADAM17-dependent cleavage in normal biology and disease, the physiological cues that trigger its activity, the effector pathways that promote its function, and the mechanisms that control its activity, particularly the role of phosphorylation, remain unresolved.Preventing this phosphorylation event by expression of a nonphosphorylatable ADAM17(S811A) mutant or expression of a tail-minus construct inhibits A1AR-stimulated, ADAM17-dependent HB-EGF cleavage.Furthermore, expression of ADAM17(S811A) in bladder tissues impairs A1AR-induced apical exocytosis.
Affiliation: Departments of Medicine and Cell Biology, University of Pittsburgh, Pittsburgh, PA 15261.Show MeSH
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Mentions: In summary, we propose the following model for the role of ADAM17 and the role of Ser-811 phosphorylation in A1AR-stimulated exocytosis in umbrella cells. In the quiescent state, before adenosine stimulation (or stretch, in the case of rat umbrella cells), ADAM17 at the apical surface may be kept in its inactive, dimeric state by the inhibitory effects of TIMP3 (Figure 7A; Xu et al., 2012). As a result of its increased production (or decreased turnover), adenosine binds to the A1AR, triggering a Gi → Gβγ → PLC → PKC pathway, which leads to phosphorylation at Ser-811 in the cytoplasmic domain of ADAM17 (Figure 7B). This leads to activation of ADAM17, possibly by altering its conformation and/or its association with regulatory proteins (e.g., TIMP3) and/or its substrates. Although not shown, signaling pathways downstream of the A1AR are also likely to function by regulating other processes (e.g., “activation” of HB-EGF). This could explain why ADAM17S811D-HAr was unable to stimulate HB-EGF release in the absence of CCPA stimulation. Finally, in its activated state, ADAM17 cleaves and releases HB-EGF, which binds to the EGFR, promoting autophosphorylation of EGFR Y1173, ultimately leading to downstream ERK1/2 activation, protein synthesis, and exocytosis (Figure 7B).
Affiliation: Departments of Medicine and Cell Biology, University of Pittsburgh, Pittsburgh, PA 15261.