Hepatitis B virus transactivator MHBst: activation of NF-kappa B, selective inhibition by antioxidants and integral membrane localization.
C-terminal truncation of the middle surface antigen from hepatitis B virus (MHBs) gives rise to a novel transactivating protein, called MHBst. In this study we show that MHBst like the HBx protein of HBV, can cause nuclear appearance of NF-kappa B DNA binding activity and induce various kappa B-controlled reporter genes. While an inhibitor of protein kinase C could not block gene induction by MHBst, the antioxidants N-acetyl-L-cysteine (NAC) and pyrrolidine dithiocarbamate (PDTC) could potently suppress transactivation at mM and microM concentrations, respectively. Also, kappa B-dependent gene induction by the transactivator HBx was blocked. The effects were selective because PDTC did not interfere with MHBst and HBx-induced activation of the c-fos promoter/enhancer, nor with the basal activity of several other reporter genes lacking functional NF-kappa B binding motifs. Our data suggest that induction of a prooxidant state is crucial for the activation of NF-kappa B by MHBst and HBx and might be related to the hepatocarcinogenic potential of the viral proteins. MHBst had a subcellular localization unusual for a viral transactivator: it appeared to be an integral membrane protein of the endoplasmic reticulum.
Meyer
M
M
Max-Planck-Institute for Biochemistry, Department of Virus Research, Martinsried, Germany.
Caselmann
W H
WH
Schlüter
V
V
Schreck
R
R
Hofschneider
P H
PH
Baeuerle
P A
PA
D000111:Acetylcysteine / Q000494:pharmacology*; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006367:HeLa Cells; D006514:Hepatitis B Surface Antigens / Q000235:genetics / Q000378:metabolism*; D006515:Hepatitis B virus / Q000187:drug effects / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism*; D009838:Oligodeoxyribonucleotides; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011759:Pyrrolidines / Q000494:pharmacology*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013859:Thiocarbamates / Q000494:pharmacology*; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D000975:Antioxidants; D006514:Hepatitis B Surface Antigens; D016328:NF-kappa B; D009838:Oligodeoxyribonucleotides; D011759:Pyrrolidines; D011993:Recombinant Fusion Proteins; D013859:Thiocarbamates; D015534:Trans-Activators; C020972:pyrrolidine dithiocarbamic acid; D015500:Chloramphenicol O-Acetyltransferase; D011493:Protein Kinase C; D000111:Acetylcysteine