A SARCOMA-DERIVED PROTEIN REGULATES HEPATOCYTE METABOLISM VIA AUTOCRINE PRODUCTION OF TUMOR-NECROSIS-FACTOR-ALPHA

Objective The effects of conditioned media from the methylcholanthrene (MCA) fibrosarcoma on hepatocyte albumin production and amino acid tr ansport were studied. The authors characterized a factor responsible f or the observed effects and investigated the role of tumor necrosis fa ctor-alpha (TNF-alpha) in these events. Summary Background Data Cancer cachexia is mediated in part by TNF-alpha. However, few tumors secret e TNF-alpha, implicating host production of this cytokine in response to as yet uncharacterized tumor-derived factors. Autocrine production of TNF-alpha recently has been described as a potent mechanism for orc hestrating hepatic metabolism. Methods Conditioned media from the MCA fibrosarcoma was incubated with isolated primary rat hepatocytes. Albu min production and TNF-alpha production by hepatocytes was measured by enzyme-linked immunosorbent assay and amino acid transport assayed by tritium (H-3)-labeled amino acid uptake. Dialysis membranes ranging f rom 3 kD to 100 kD were used to determine the size of the factor/facto rs responsible for the observed effects. Results Conditioned media fro m the MCA fibrosarcoma contained no TNF-alpha whereas treatment of pri mary rat hepatocytes with the conditioned media resulted in a 53-fold increase in TNF-alpha production by hepatocytes compared with control. Treatment of hepatocytes with MCA fibrosarcoma-conditioned media resu lted in decreases in hepatic albumin production of 46%, 61%, and 42% o ver 3 days of treatment, and these effects were reversible by the addi tion of antibody to TNF-alpha. Treatment of hepatocytes with MCA fibro sarcoma conditioned media resulted in increases in hepatocyte amino ac id transport via inductions of System N (1.87 fold) and System A(1.93 fold). These effects were partially abrogated by the addition of antib ody to TNF-alpha. Dialysis experiments determined the molecular weight of the factor or factors responsible for the observed effects to be g reater than 100 kD. The effects of the MCA fibrosarcoma conditioned me dia were abolished by both trypsin treatment and heat inactivation, in dicating the protein nature of the factor being studied. Conclusions A tumor-derived protein has been isolated from the MCA fibrosarcoma. Th e protein inhibits hepatocyte albumin production and increases amino a cid transport in vitro via the autocrine production of TNF-alpha.