Nicotinic receptor‐associated modulation of stimulatory and inhibitory neurotransmitters in NNK‐induced adenocarcinoma of the lungs and pancreas

Abstract

Small airway-derived pulmonary adenocarcinoma (PAC) and pancreatic ductal adenocarcinoma (PDAC) are among the most common human cancers and smoking is a risk factor for both. Emerging research has identified cAMP signalling stimulated by the stress neurotransmitters adrenaline and noradrenaline as an important stimulator of adenocarcinomas, including PAC and PDAC. The nicotine-derived nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is a potent mutagen and the most powerful tobacco carcinogen. NNK is also an agonist for nicotinic acetylcholine receptors (nAChRs). Using hamster models of NNK-induced PAC and PDAC, we have tested the hypothesis that in analogy to chronic effects of nicotine in the brain, NNK may modulate the alpha(7)- and alpha(4)beta(2)nAChRs, causing an increase in stress neurotransmitters and a decrease in the inhibitory neurotransmitter gamma-aminobutyric acid (GABA). Immunoassays showed a significant increase in serum adrenaline/noradrenaline and increased intracellular cAMP in the cellular fraction of blood of NNK-treated hamsters. Western blots on microdissected control small airway epithelia, alveolar epithelia, pancreatic islet and pancreatic duct epithelia, and from NNK-induced PACs and PDACs showed that the GABA-synthesizing enzyme glutamate decarboxylase 65 (GAD65) and GABA were suppressed in NNK-induced PACs and PDACs. In contrast, protein expression of the alpha(7)nAChR, alpha(4)nAChR as well as p-CREB and p-ERK1/2 were up-regulated. These findings suggest that NNK-induced alterations in regulatory nAChRs may contribute to the development of smoking-associated PAC and PDAC by disturbing the balance between cancer-stimulating and -inhibiting neurotransmitters.