Synthesis of the Ninth Component of Complement by a Clonal Strain of Rat Hepatoma Cells

Abstract

The MH₁C₁ strain of rat hepatoma cells was found to produce the ninth component of complement (C9). Most of the C9 produced by the cells was secreted into the culture medium. The production of C9 by MH₁C₁ cells was temperature sensitive with a Q₁₀ of 2.2. Cycloheximide completely inhibited the production of C9 within 6 hr. Removal of cycloheximide at 24 hr resulted in a rapid return of C9 production. The production of C9 was also inhibited by treatment of the cells with actinomycin D. Hydrocortisone (3 × 10^-6 M), which stimulates the production of serum albumin by MH₁C₁ cells 4- to 5-fold, did not increase C9 production. C9 produced by MH₁C₁ cells in culture was similar to guinea pig and rat serum C9 when comparisons were made by density gradient ultracentrifugation, by inhibition of hemolytic activity by antrypol, and by kinetic analysis of the reaction between C9 and EAC14235678. The results of these studies show that MH₁C₁ hepatoma cells synthesize C9 and secrete this complement component into the culture medium by processes that require both protein and RNA synthesis.