High level expression of p55, a thyroid hormone binding protein which is homologous to protein disulfide isomerase in a retroviral vector.

To develop an efficient system for a high level expression of a human cellular thyroid hormone binding protein (p55) in eukaryotic cells, a full-length p55 cDNA was inserted into a Harvey murine sarcoma virus-derived vector (pHTBr) and transfected into mouse NIH 3T3 cells. The expressed p55 has a molecular weight of 55,000 and is recognized by the human specific anti-p55 monoclonal antibody. Similar to the endogenous p55, the expressed p55 is localized on endoplasmic reticulum and nuclear envelope. Moreover, p55 was specifically labeled by N-bromoacetyl-3,3',5-triiodo-L-thyronine. Thus, the expressed p55 is structurally indistinguishable from the endogeneous p55. pHTBr was packaged into a virus with the aide of an amphotropic virus. Infection by pHTBr-containing virus yielded a 2-11 fold higher expression than the endogeneous p55 in NIH3T3, rat GH3, human HepG2 cells and a mouse monoclonal antibody secreting hybridoma.