Regulation of D-0-Hydroxybutyrate Dehydrogenase in Rat Hepatoma Cell Lines

Quantitation of i>-/3~liy butvratc dehydrogenase (BDH) in normal rat hepatocytes was compared with that in two rat hepatoma cell lines, H4-II-EC3 and RLT-3C. BDH activity in normal rat hepatocyte mito chondria was 321 nmol/min/mg, which was greatly reduced to 10.7 nmol/ min/mg and 1.7 nmol/min/mg in H4-II-EC3 and RLT-3C cell mitochon dria, respectively. The cell growth rate and L-[35Slmethionineincorpora tion rate showed that RLT-3C cells had the highest growth rate (32.4-h doubling time) and the fastest protein biosynthesis rate (2.65 x 10s cpm/ min/106 cells). The H4-II-EC3 cell line grew more slowly (48.5-h dou bling time) and had lower protein biosynthesis rate (1.46 x IO5cpm/min/ Id'1cells). The protein synthesis rate in hepatocytes was 1.25 x 10s cpm/ min/106 cells. These results suggest that there is a reciprocal correlation between BDH activity and cell growth and protein synthesis rates. Immunochemical quantitation of BDH showed the amount of BDH in H4-II-EC3 and RLT-3C cells was about 4.8 and 0.5% of that in normal rat hepatocytes, respectively. Quantitation of BDH by biosynthesis in dicated that BDH content in H4-II-EC3 cells and RLT-3C cells was 9.3 and 4.0% of that of normal hepatocytes, respectively. Precursor BDH synthesized by in vitro translation primed with RNA of H4-II-EC3 cells or RLT-3C cells was 3.0 and 1.1% of that translated from normal rat hepatocyte RNA. These results suggest that the decrease in BDH content in hepatoma cells results from a decrease in functional BDH-mRNA. The coupling of a decrease in BDH activity with an increase in activity of succinyl-CoA: acetoacetyl-CoA transferase in hepatoma cells may play a role in generating additional energy required for the rapid growth of tumor cells.