HSV-2 Increases the Mitochondrial Aspartate Amino Transaminase Characteristic of Tumor Cells

Abstract

A set of polypeptides has previously been described as being immunoprecipitated from tumor cell lysates by the sera of tumor-bearing animals (TBS) or by antisera raised to herpes simplex virus type 2 (HSV-2)-infected cells. These polypeptides were not immunoprecipitated from control cells. The principal polypeptides detected of MW 200, 90 (U90 and L90), 40, and 32 kDa were increased by HSV-2 infection. This communication describes the purification of the 40-kDa protein and its identification by amino acid sequence analysis as being homologous to the mature form of mitochondrial aspartate amino transaminase (mAAT). Two different forms of mAAT were purified and sequenced. One form, of low abundance, was immunoprecipitated by TBS and corresponded to the 40-kDa protein immunoprecipitated from tumor, but not control, cell lysates. Western blotting of the 40-kDa protein immunoprecipitated by TBS showed that it was a form of mAAT found only in tumor cells. The other abundant form reacted in Western blots with antibody to mAAT and was clearly the constitutive enzyme, present in all cells. In general, mAAT was increased up to fourfold after infection with HSV-2. HSV-2 infection also increased mAAT enzyme activity. Northern blotting and quantitative PCR showed that mAAT was induced by HSV-2 at the level of transcription. The specific form of mAAT immunoprecipitated from tumor, but not control, cell lysates could have a role in tumorigenesis, could be a putative tumor cell marker, or could be a target for antitumor drugs. HSV-2 probably induces enzymes of glutamine metabolism because HSV-2 requires glutamine for growth, thus revealing potential new antiviral targets.