alpha 7 nicotinic acetylcholine receptor in tumor-associated macrophages inhibits colorectal cancer metastasis through the JAK2/STAT3 signaling pathway

摘要

Considerable evidence has implied that alpha 7 nicotinic receptor subtypes play an important role in chronic inflammatory and neuropathic pain signaling. The aim of the present study was to determine the role of endogenous alpha 7nAChR signaling in tumor-associated macrophages (TAMs) in human colorectal cancer (CRC) metastasis and prognosis. alpha 7nAChR expression in primary tumor cells and adjacent stroma cells especially in TAMs in 51 CRC patients was observed. Using a human monocyte THP-derived macrophages (TMs) with alpha 7nAChR-siRNA knockdown (TM alpha 7(-/-)) and a CRC cell Transwell co-culture model, the migration and invasion of two CRC cells, LoVo and SW620, were determined. Western blotting was carried out to investigate the expression of multiple molecules involved in the NF-kappa B, STAT3, PI3K signaling pathways in mimic TAMs, i.e., TMs exposed to in-direct LoVo cell stimulation. A nicotinic alpha 7 receptor antagonist [alpha-bungarotoxin (alpha-Btx)] and three pharmaceutical inhibitors: AG490 (JAK2/STAT3 inhibitor), LY294002 (PI3K inhibitor) and Bay 11-7082 (NF-kappa B inhibitor) were applied to evaluate whether these signaling pathways were associated with the enhanced migration of CRC cells when co-cultured with alpha 7nAChR knockdown TMs. The results revealed that the expression of alpha 7nAChR in TAMs differed in patients. However, CRC patients who had a high incidence of hepatic metastasis showed no or low expression of alpha 7nAChR in TAMs. TMs with alpha 7nAChR-siRNA knockdown (TM alpha 7(-/-)) significantly enhanced the migration and invasion of the two CRC cell lines LoVo and SW620. alpha 7nAChR knockdown in TMs significantly downregulated phosphorylation of STAT3, PI3K p85 and NF-kappa B p65 after co-culturing with LoVo cells. Inhibition of JAK2/STAT3 prevented the TM alpha 7(-/-)-enhanced migration of LoVo cells. alpha 7nAChR expressed in TAMs in human CRC patients plays an important role in preventing metastasis and could be a prognostic marker in CRCs, which may be regulated by the JAK2/STAT3 signaling pathway.