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Cholinergic agonists transactivate EGFR and stimulate MAPK to induce goblet cell secretion
Harumi Kanno1, Yoshitaka Horikawa, Robin R Hodges
1Schepens Eye Research Institute, Department of Ophthalmology, Harvard Medical School, Boston, Massachusetts 02114, USA.
American Journal of Physiology. Cell Physiology
|March 7, 2003
Summary
Cholinergic agonists stimulate conjunctival goblet cell mucin secretion via the epidermal growth factor receptor (EGFR) and p42/p44 mitogen-activated protein kinase (MAPK) pathway. This research clarifies the signaling mechanisms controlling tear film mucus production.
Area of Science:
- Ophthalmology
- Cell Biology
- Neuroscience
Background:
- Conjunctival goblet cells produce mucins, crucial for the tear film's mucous layer.
- Goblet cell mucin secretion is regulated by the nervous system, particularly parasympathetic agonists.
- The specific intracellular signaling pathways involved in this neural control are not fully understood.
Purpose of the Study:
- To investigate the role of p42/p44 mitogen-activated protein kinase (MAPK) in cholinergic agonist-stimulated conjunctival goblet cell mucin secretion.
- To elucidate the intracellular signaling cascade initiated by cholinergic agonists.
Main Methods:
- Rat conjunctiva explants were stimulated with carbachol, a cholinergic agonist.
- Inhibitors of MAPK (U-0126), muscarinic receptors (pirenzepine, gallamine, 4-DAMP), Src kinase (PP1), and EGFR (AG-1478) were used.
- Intracellular calcium levels were manipulated using a calcium ionophore and extracellular calcium chelation.
- Phosphorylation of MAPK, Pyk2, p60Src, and EGFR was assessed.
Main Results:
- Carbachol significantly stimulated MAPK phosphorylation in a time- and dose-dependent manner.
- MAPK activation and carbachol-induced secretion were completely blocked by the MAPK inhibitor U-0126.
- Muscarinic receptor antagonists partially inhibited carbachol-stimulated MAPK activation.
- Increased intracellular calcium enhanced MAPK activation, while extracellular calcium chelation inhibited it.
- Carbachol increased tyrosine phosphorylation of Pyk2, p60Src, and EGFR.
- Inhibition of Src kinase and EGFR blocked carbachol-stimulated MAPK activation and secretion.
Conclusions:
- Cholinergic agonists stimulate conjunctival goblet cell mucin secretion through the activation of the MAPK pathway.
- This process involves the transactivation of the epidermal growth factor receptor (EGFR) to activate MAPK.
- Pyk2 and p60Src may play a role in the EGFR transactivation process.