Hepatocyte growth factor production by neutrophils infiltrating bronchioloalveolar subtype pulmonary adenocarcinoma: role in tumor progression and death.

ABSTRACT

Increased numbers of tumor-infiltrating neutrophils are linked to poorer outcome in patients with adenocarcinoma of the bronchioloalveolar carcinoma (BAC) subtype. Hepatocyte growth factor (HGF) is a pleiotropic cytokine operating through activation of the proto-oncogene c-met and is a factor of poor prognosis in various cancers. Reports that neutrophils produce HGF led us to investigate their participation in the aerogenous spread of tumor cells and the prognosis of BAC, through the effect of HGF on c-met-expressing tumor cells. Immunoreactive HGF was detected in bronchoalveolar lavage fluid (BALF) supernatants from 34 of 36 patients, whereas it was undetectable in BALF from healthy controls. The HGF thus detected was locally produced, because HGF mRNA was expressed by the patients' fresh alveolar cells, and HGF protein was detected in 24-h culture supernatants. In immunocytochemical studies of BALF cytospin preparations and tumor specimens from the patients, neutrophils were always HGF-positive, whereas alveolar macrophages and tumor cells gave inconsistent results. Alveolar neutrophil-derived HGFs induced significant, concentration-dependent migration of BAC-derived tumor cells in vitro, and this effect was inhibited by anti-HGF neutralizing antibodies. Granulocyte-macrophage colony-stimulating factor and tumor necrosis factor alpha (present in the lung tumor microenvironment) provoked HGF release from neutrophil intracellular stocks, and the capacity of blood neutrophils from BAC patients to produce HGF was unaltered. Immunochemical studies of c-met expression in BALF cytospin preparations and tumor sections showed that most HGF receptor-bearing cells were tumor cells. High HGF levels in BALF supernatants were significantly associated with poorer outcome in patients with BAC and were an independent predictor of clinical outcome in multivariate analysis. Altogether, our results support the notion that BAC generates a local environment that attracts functionally normal neutrophils from peripheral blood and leads to neutrophil release of biologically active HGF on contact with HGF receptor-expressing tumor cells, thereby contributing to poorer patient outcome.