title: Thrombin activates envelope glycoproteins of HIV type 1 and enhances fusion.
abstract: To elucidate the roles of serine proteases, including thrombin, in HIV infection, we treated H9 cells infected with HIV-1 LAI virus (H9/IIIB) with four different proteases (thrombin, cathepsin G, trypsin and chymotrypsin) and observed their effects on functional epitopes on both gp120 and gp41 by using flow cytometry. Monoclonal antibodies (MAbs) against the V3 loop, V2 loop, CD4 binding site, coreceptor binding site and gp41 were used. It was found that trypsin decreased the binding of all MAbs except for one MAb against the V3 loop (IIIB-V3-21). Chymotrypsin and cathepsin G did not show any remarkable effect on the antigen expression. On the other hand, thrombin decreased the reactivities of two out of four anti-V3 MAbs and increased the exposure of functional gp120 epitopes including the coreceptor binding site and CD4 binding site. Thrombin also increased the expression of 2F5 antigen (a neutralizing epitope of gp41) but had no effect on other gp41 epitopes. The effect of trypsin or thrombin on HIV-induced cell fusion was examined through co-culturing H9/IIIB and MAGI cells. Trypsin slightly inhibited fusion. Fusion was significantly enhanced in a dose-dependent manner by thrombin, and a 280% increase at 5 U/ml (P < 0.001) was observed. In conclusion, thrombin, one of the major inflammatory molecules in blood, facilitates HIV-induced cell fusion, probably by activating gp120.
authors.affiliation: Division of Allergy and Infectious Diseases, Department of Internal Medicine, Graduate School of Medicine, Tohoku University, 1-1Seiryo-Machi, Aoba-ku, Sendai 980-8574, Japan.
authors.forename: Hong
authors.initials: H
authors.lastname: Ling
authors.forename: Peng
authors.initials: P
authors.lastname: Xiao
authors.forename: Osamu
authors.initials: O
authors.lastname: Usami
authors.forename: Toshio
authors.initials: T
authors.lastname: Hattori
mesh_terms: D000911:Antibodies, Monoclonal; D056649:Cathepsin G; D002403:Cathepsins / Q000378:metabolism; D002459:Cell Fusion; D002460:Cell Line; D002918:Chymotrypsin / Q000378:metabolism; D000939:Epitopes / Q000276:immunology; D005434:Flow Cytometry; D015699:HIV Envelope Protein gp120 / Q000276:immunology / Q000378:metabolism*; D015700:HIV Envelope Protein gp41 / Q000276:immunology / Q000378:metabolism*; D015497:HIV-1 / Q000254:growth & development / Q000472:pathogenicity*; D006801:Humans; D010446:Peptide Fragments / Q000276:immunology / Q000378:metabolism*; D012697:Serine Endopeptidases; D013917:Thrombin / Q000378:metabolism*; D014357:Trypsin / Q000378:metabolism
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D015699:HIV Envelope Protein gp120; D015700:HIV Envelope Protein gp41; C098314:HIV envelope glycoprotein gp41 (593-603); C059762:HIV envelope protein gp120 (305-321); D010446:Peptide Fragments; D002403:Cathepsins; D012697:Serine Endopeptidases; D002918:Chymotrypsin; C534094:CTSG protein, human; D056649:Cathepsin G; D014357:Trypsin; D013917:Thrombin