Production of nerve growth factor by mouse hepatocellular carcinoma cells and expression of TrkA in tumor-associated arteries in mice

Background & Aims: Nerve growth factor (NGF) has been suggested to play a role in cancer progression. We found that NGF is specifically elevated in mouse hepatocellular carcinomas (HCCs) by cDNA array analysis. The present study aimed to elucidate expression of NGF and its receptors during hepatocarcinogenesis and under other conditions. Methods: Expression of NGF, TrkA, and p75NTR was investigated in HCCs developing and regenerating livers, and primary hepatocyte cultures in B6C3F1 mice by reverse-transcription polymerase chain reaction, Northern blotting, and/or immunohistochemistry. The biological activity of NGF produced by the HCC cells was studied by using PC12 cells. Nerve fibers in hepatic tumors were immunohistochemically examined. Results: Although NGF was negative in adult and developing livers, it was markedly elevated in focal hepatocytic lesions from early stages of carcinogenesis. Appreciable levels were also detected in regenerating livers and hepatocytes in culture. The conditioned medium of HCC cells caused PC12 neurite outgrowth, but this was reduced on pretreatment of the conditioned medium with an anti-NGF antibody or NGF antisense expression in HCC cells. Although neither TrkA nor p75NTR was detectable in either HCC or normal hepatic cells, TrkA was shown in the walls of tumor-associated arteries that contain abundant nerve fibers. Conclusions: NGF is expressed by hepatocytes during carcinogenesis, regeneration, and primary culture but may have cells other than hepatocytes as the target. TrkA expression and the abundance of nerve fibers in the walls of tumor-associated arteries suggest a possible role for NGF in angiogenesis.GASTROENTEROLOGY 2002;122:1978-1986