AUTOCRINE REGULATION OF ERYTHROPOIETIN GENE-EXPRESSION IN HUMAN HEPATOCELLULAR-CARCINOMA CELLS

We have previously reported that a marked increase in erythropoietin ( Epo) production can be demonstrated in Hep3B cell cultures in response to hypoxia (1). In order to determine whether this increase involves an autocrine mechanism, we have investigated the effects of purified h uman recombinant Epo (rHuEpo) on Epo production. Purified rHuEpo (5-80 mU/ml) produced a significant increase above control levels of Epo in Hep3B cell cultures under normoxic (20% O-2) conditions. Hypoxic (1% O-2) incubation ofHep3B cells with rHuEpo caused an increase over cont rol levels of EpomRNA. Hep3B cells also expressed Epo receptor (Epo-R) transcripts. Binding studies using [I-125]-Epo revealed that Hep3B ce lls contain a single class of binding site (kd=2.9 nmol/L and Bmax=176 0 sites/cell). Antierythropoietin receptor monoclonal antibody inhibit ed the rHuEpo induced elevation in medium levels of Epo and blocked [( 125)]-Epo binding to Hep3B cell membranes. These results demonstrate t hat the expression of EpomRNA may be controlled, at least in part, by an autocrine mechanism.