PT  - JOURNAL ARTICLE
AU  - Mikihito Kajiya
AU  - Isao Ichimonji
AU  - Christine Min
AU  - Tongbo Zhu
AU  - Jun-O Jin
AU  - Qing Yu
AU  - Soulafa A Almazrooa
AU  - Seunghee Cha
AU  - Toshihisa Kawai
TI  - Muscarinic Type 3 Receptor Induces Cytoprotective Signaling in Salivary Gland Cells Via EGFR Transactivation
AID  - 10.1124/mol.111.077354
DP  - 2012 Apr 17
TA  - Molecular Pharmacology
PG  - mol.111.077354
4099  - http://molpharm.aspetjournals.org/content/early/2012/04/17/mol.111.077354.short
4100  - http://molpharm.aspetjournals.org/content/early/2012/04/17/mol.111.077354.full
AB  - Muscarinic type 3 receptor (M3R) plays a pivotal role in the induction of glandular fluid secretions. While M3R is often the target of autoantibody in Sjogren's syndrome (SjS), chemical agonists for M3R are clinically used to stimulate the saliva secretion in SjS patients. Nonetheless, aside from its activity in promoting glandular fluid secretions, it is unclear whether activation of M3R is related to other biological events in SjS. This study aimed to investigate the cytoprotective effect of chemical-agonist-mediated M3R-activation on apoptosis induced in human salivary gland (HSG) cells. Carbachol (CCh), a muscarinic receptor specific agonist, abrogated TNFα/IFNγ-induced apoptosis via pathways involving caspase3/7, but its cytoprotective effect was diminished by M3R antagonist (4-DAMP), MEK-ERK inhibitor (U0126), PI3K-Akt inhibitor (LY294002), or EGFR inhibitor (AG1478). Ligation of M3R with CCh transactivated EGFR and phosphorylated ERK and Akt, the downstream target of EGFR. Inhibition of intracellular calcium release or PKC δ, both of which are involved in the cell signaling of M3R-mediated fluid secretion did not affect CCh-induced ERK- and Akt-phosphorylation. On the other hand, CCh stimulated the phosphorylation of Src and Src-binding to EGFR. Importantly, Src inhibitor (PP2) attenuated the CCh/M3R-induced cytoprotective effect and EGFR transactivation cascades. Overall, these results indicated that CCh/M3R induced transactivation of EGFR via Src activation, leading to ERK- and Akt-phosphorylation which, in turn, suppressed caspase3/7-mediated apoptotic signals in HSG cells. Therefore, this study, for the first time, proposes that CCh-mediated M3R activation can promote not only fluid secretion but also survival of salivary gland cells in the inflammatory context of SjS.