GP73, a novel Golgi-localized protein upregulated by viral infection

We report the isolation and characterization of GP73, a novel 73 kDa human Golgi protein. The GP73 cDNA was cloned by differential screening of a cDNA library derived from the liver of a patient with adult giant-cell hepatiti s (GCH), a rare form of hepatitis with presumed viral etiology. In vitro tr anscription-translation studies indicate that GP73 is an integral membrane protein, and immunolocalization experiments using epitope-tagged GP73 demon strate that the protein is localized to the Golgi apparatus. Northern blot analysis of RNA from multiple human tissues reveals a single GP73 mRNA tran script with a size of approximately 3.0 kb. Immunohistochemical studies usi ng rabbit polyclonal antisera directed against recombinant GP73 demonstrate that the protein is preferentially expressed by epithelial cells in many h uman tissues. In normal livers, GP73 is consistently present in biliary epi thelial cells, whereas hepatocytes show little or no signal. In contrast, l ivers of patients with GCH display strong GP73 immunoreactivity in multinuc leated hepatocytes. GP73 mRNA and protein are expressed in highly different iated HepG2 hepatoma cells after infection with adenovirus in vitro. We con clude that GP73 represents a novel, epithelial cell-specific integral membr ane Golgi protein that can be upregulated in response to viral infection. ( C) 2000 Elsevier Science B.V. All rights reserved.