EXPRESSION OF MESSENGER-RNA FOR 3 BOMBESIN RECEPTOR SUBTYPES IN HUMAN BRONCHIAL EPITHELIAL-CELLS

Gastrin-releasing peptide (GRP), the mammalian form of the amphibian peptide bombesin, may act as a growth-regulatory peptide in the lung. Cultured human bronchial epithelial (HBE) cells have previously been found to proliferate in response to GRP or bombesin. Three receptors have been identified for bombesin and its analogs, namely gastrin-releasing peptide receptor (GRPR), neuromedin B receptor (NMBR), and bombesin receptor subtype 3 (BRS-3). The human genes for these receptors have been cloned and sequenced. We used the polymerase chain reaction to detect transcripts for these three receptor subtypes in HBE cells cultured from bronchial mucosal biopsies. Primers specific for each receptor subtype were used to amplify DNA fragments from reverse-transcribed mRNA isolated from these cultures. An amplified fragment was detected for GRPR in seven of nine cases, for NMBR in six of 10 cases, and the BRS-3 in three of nine cases. We have also amplified message for NMBR in five of five fresh bronchial biopsies, but message for GRPR could not be detected. In preliminary evaluation of two biopsies, there was also no evidence of BRS-3 expression. Additionally, we have detected transcripts for GRPR and NMBR in four of seven and seven of seven cases, respectively, of cultured non-small cell lung carcinomas (NSCLC). BRS-3 expression was seen in one of seven carcinomas in culture. Identity of the amplified fragments was confirmed by restriction enzyme digestion and Southern blotting. Furthermore, GRP induced expression of the early-response gene, c-jun, in an HBE cell culture and an NSCLC cell line. GRP also promoted colony formation in die NSCLC cells. These results provide further evidence that GRP and related neuropeptides may function as growth-modulating factors in human adult bronchial mucosa and may be important in the development of non-small cell lung cancer.