Expression of nicotinic receptors in normal and tumoral pulmonary neuroendocrine cells (PNEC)

Neuroendocrine (NE) tumors of the lung represent a wide spectrum of phenotypically distinct entities, with differences in tumor progression and aggressiveness, which include carcinoid tumor (CT) and small-cell lung carcinoma (SCLC). Approximately 20–40% of patients with both typical and atypical CT are non-smokers, while virtually all patients with SCLC are cigarette smokers. Cigarette smoke contains numerous molecules which have been identified as carcinogens. The real impact of nicotine in the development of tumors is not well known. Recent studies show that nicotine upregulates factors of transcription through the nicotinic receptors. The aim of our work was to study the expression of the nicotinic receptors in normal and neoplastic pulmonary NE cells. An immunohistochemical study was carried out with antibodies against NE markers and subunits α7 and β2 of nicotinic receptors in 7 normal lungs, 10 CT (8 typical and 2 atypical) and 10 SCLC fixed in formalin and embedded in paraffin. This study was completed with reverse transcription-polymerase chain reactions (RT-PCR) detection of α7-subunit nicotinic receptor mRNA expression. Our data showed that β2-subunit of nicotinic receptors is never expressed in normal NE cells of lungs and very rarely in NE tumors. In contrast, α7-subunit is constantly found in NE cells in normal lungs. In tumors, its expression is significantly higher in SCLC than in CT (p=0.009). Thus, α7 subunit nicotinic receptor in a context of chronic nicotinic intoxication seems to be associated with an aggressive phenotype in the spectrum of the NE tumors.