Blocking M2 muscarinic receptor signaling inhibits tumor growth and reverses epithelial-mesenchymal transition (EMT) in non-small cell lung cancer (NSCLC)

Abstract

Lung cancers express non-neuronal, cholinergic autoparacrine loop, which facilitates tumor growth. Interruption of M3 muscarinic cholinergic signaling has been reported to inhibit small cell lung cancer (SCLC) growth. The purpose of this study is to investigate if blocking autoparacrine muscarinic cholinergic signaling could inhibit non-small cell lung cancer (NSCLC) growth and possible underlying mechanisms. Our results showed that PC9 and A549 cells expressed all 5 subtypes of muscarinic receptor (mAChR) and blocking M2 mAChR (M2R) signaling using selective antagonist methoctramine or short hairpin RNA (shRNA) inhibited tumor cell proliferation in vitro and in vivo. Consistent with AChR agonists stimulating p44/42 MAPK (Erk1/2) and Akt phosphorylation, blocking M2R signaling decreased MAPK and Akt phosphorylation, indicating that non-neuronal ACh functions as an autoparacrine growth factor signaling in part through activation of M2R and downstream MAPK and Akt pathways. Importantly, further studies revealed that blocking M2R signaling also reversed epithelial-mesenchymal transition (EMT) in vitro and in vivo, indicating that non-neuronal ACh promotes EMT partially through activation of M2R. These findings demonstrate that M2R plays a role in the growth and progression of NSCLC and suggest M2R antagonists may be an efficacious adjuvant therapy for NSCLC.

Keywords:

• autoparacrine
• AKT
• epithelial-mesenchymal transition
• MAPK ERK
• M2 muscarinic receptor
• non-neuronal acetylcholine
• non-small cell lung cancer

Disclosure of Potential Conflicts of Interest

No potential conflicts of interest were disclosed.

Funding

This work was supported by National Natural Science Foundation of China (81173084 and 81372522), Science and Technology Commission of Shanghai Municipality (12ZR1416000 and 12140901400), and International Science & Technology Cooperation Program of China (2011DFA33180).

Supplemental Material

Supplemental data for this article can be accessed on the publisher's website.