Comparison of in vivo translation rates and messenger RNA levels of alpha2U-globulin in rat liver and Morris hepatoma 5123D

Abstract

The synthesis of the male rat hepatic protein alpha2U-globulin has been examined in Morris hepatoma 5123D and male host liver using pulse incorporation of labeled amino acids in vivo, followed by immunoprecipitation of the newly synthesized alpha2U-globulin from the soluble protein fraction of liver and hepatoma tissue. It was found that no alpha2U-globulin synthesizes alpha2U-globulin at a normal level (0.9 to 1.0% of total hepatic protein synthesis). A variety of liver-derived cell culture lines also did not have alpha2U-globulin synthesis. The level of the specific mRNA coding for alpha2U-globulin can be quantitated using in vitro translation of polyadenylate-containing RNA in a Krebs II ascites cell-free translational system, followed by immunoprecipitation of the alpha2U-globulin synthesized in vitro. Using this technique, it was found that host liver contained alpha2U-globulin mRNA at normal levels, whereas hepatoma tissue contained no detectable mRNA coding for this protein. Thus, alpha2U-globulin synthesis is deleted in the minimal-deviation hepatoma 5123D as a consequence of the inability of that tissue to produce functional mRNA coding for alpha2U-globulin. The implications for the regulation of gene expression in malignant cells are discussed.