Human endogenous retrovirus K10: expression of Gag protein and detection of antibodies in patients with seminomas.
The human endogenous retrovirus K10 (HERV-K10) has been identified in the human genome by its homology to retroviruses of other vertebrates (M. Ono, T. Yasunaga, T. Miyata, and H. Ushikubo, J. Virol. 60:589-598, 1986). Using PCR amplification, DNA cloning, sequencing, and procaryotic expression, we were able to demonstrate that HERV-K10 encodes a 73-kDa protein which was processed by a HERV-K10-encoded protease to yield proteins p22/p26, p30, and p15/16. Analysis of the teratocarcinoma cell line Tera 1 or tumor tissues by immunoblotting demonstrated that the 80-kDa polyprotein of HERV-K10 gag and a processed protein of 39 kDa were expressed. In addition, a major protein of 39 kDa and additional species of 30, 22, 19, and 17 kDa could be detected in the supernatant of Tera 1 cells, suggesting that HERV-K10 Gag proteins are either secreted or processed to probably incomplete viral particles. In addition, the gag gene of HERV-K10 was expressed in the baculovirus system. Using this recombinant system to test antisera from patients with different diseases and healthy individuals, we were able to detect antibodies against the N-terminal part of HERV-K10 Gag in 2 to 4% of groups of tumor patients with titers ranging between 1:80 and 1:640, while approximately 0.1 to 0.5% of healthy individuals exhibited antibodies with lower titers. In contrast, patients with seminoma had antibody titers in the range of 1:2,560 at the time when the tumor was detected. Immunohistochemistry using specific rabbit sera or monoclonal antibodies against HERV-K10 Gag revealed that the Gag protein is expressed in the cytoplasm of the tumor cells. Furthermore, an 80-kDa protein corresponding to the HERV-K10 Gag polyprotein could be detected in tumor biopsies. For the first time, these data indicate that HERV-K10 Gag proteins are synthesized in seminoma cells and tumors exhibit relatively high antibody titers against Gag. So far, no information on which role HERV-K10 plays in the development of this tumor exists.
Sauter
M
M
Abteilung Virologie, Universitätkliniken des Saarlandes, Homburg/Saar, Germany.
Schommer
S
S
Kremmer
E
E
Remberger
K
K
Dölken
G
G
Lemm
I
I
Buck
M
M
Best
B
B
Neumann-Haefelin
D
D
Mueller-Lantzsch
N
N
D000914:Antibodies, Viral / Q000032:analysis*; D002460:Cell Line; D015683:Gene Products, gag / Q000235:genetics* / Q000276:immunology; D006801:Humans; D011994:Recombinant Proteins / Q000276:immunology; D012190:Retroviridae / Q000276:immunology / Q000378:metabolism*; D018239:Seminoma / Q000276:immunology* / Q000378:metabolism / Q000821:virology; D013724:Teratoma / Q000276:immunology / Q000378:metabolism; D014407:Tumor Cells, Cultured
D000914:Antibodies, Viral; D015683:Gene Products, gag; D011994:Recombinant Proteins