Stimulation of fibrinogen synthesis in cultured rat hepatocytes by fibrinogen degradation product fragment D

The direct stimulation of fibrinogen biosynthesis by fibrinogen degradation produces (FDPs) was studied in rat hepatocyte cultures. Pure rat FDP fragment D (FDP-D) (M(r) 90,000) and FDP fragment E (FDP-E) M(r) 40,000) and mixtures of the two (FDP-DE) were added to rat hepatocytes cultured in serum-free hormonally defined medium. Hydrocortisone (20 μM) significantly increased synthesis of fibrinogen, as determined by incorporation of [³⁵S]methionine. FDP-D and FDP-E did not increase fibrinogen synthesis in the presence of hydrocortisone. However, hepatocytes cultured without hydrocortisone displayed increased fibrinogen synthesis (2.0- to 2.8-fold) with FDP-D (2.6-6.7 μM) but not with FDP-E (5.7 μM). At these FDP concentrations the synthesis of albumin, haptoglobin, and transferrin was not increased. FDP-D-induced fibrinogen synthesis was inhibited (>90%) by actinomycin D and cycloheximide, indicating that the increase in [³⁵S]methionine incorporation was from de novo protein synthesis. The role of FDP-D was further substantiated by showing that FDP-D, but not FDP-E, bound to the hepatocytes. These data indicate that FDP-D, but not FDP-E, directly and specifically stimulates fibrinogen synthesis in rat hepatocytes; this stimulation does not require any additional serum or protein cofactors.