NK1-R blockade and murine lung tumorigenesis. A model for studying the adenoma-carcinoma sequence

Background and aims. Originally, the aim of the present study was the evaluation of the role of NK- 1 receptor (NK-1R) in the lung fibrogenic response to BLM in mice treated with a selective receptor antagonist. The loss of function of the NK-1R in mice resulted in the development of adenocarcinoma (AC) at 21 days after BLM administration. This finding was unexpected. We used NK-1R knockout mice (NK1r–/–) to examine the role NK-1R signaling in lung tumorigenesis and to study the alterations in gene expression, which characterise the sequence of precursor lesions that precede the development of the BAC. Methods. Male NK1r–/– and wild type mice with either a C57Bl/6 or a Balb/c background were used in this study. The mice received a single intratracheal instillation of 150 lg of BLM in saline solution (50 ll) or saline. At various times after treatment, the mice were sacrificed and the lungs were excised and processed for conventional light microscopy, immunohistochemistry, biochemistry and RNase protection assay analysis. Results. We show in mice that the loss of function of the neurokinin-1 receptor (NK1-R) – due to either a pharmacological or a genetic manipulation – results in a sequence of morphological changes in response to bleomycin (BLM) treatment, which precede the development of AC. We also demonstrate that a series of alterations in gene expression of proliferation markers (i.e. PCNA and Ki-67) and cell cycle regulators (i.e. FHIT, p53 and p21) characterizes the sequence of the precursor lesions. The loss of function of the NK1-R results in changes of the apoptotic rate and in a delay of DNA breaks recovery of alveolar epithelial cell following BLM treatment. The NK1-R blockade interferes with a caspase-independent pathway of apoptosis by affecting both the translocation of Nur77 into the cytoplasm and the expression of some important Bcl2 family members such as Bcl2 and Bak. Conclusions. To our knowledge, this is the first model to demonstrate a role for NK-1R in lung epithelial cell death and tumorigenesis. This animal model may provide new information on the biology of AC and will facilitate designing and testing of new therapeutic interventions.