N-BUTYLDEOXYNOJIRIMYCIN-MEDIATED INHIBITION OF HUMAN-IMMUNODEFICIENCY-VIRUS ENTRY CORRELATES WITH IMPAIRED GP120 SHEDDING AND GP41 EXPOSURE

The alpha-glucosidase inhibitor N-butyldeoxynojirimycin (NB-DNJ) is an inhibitor of human immunodeficiency virus (HIV) replication and HIV-i nduced syncytium formation in vitro. Although an NB-DNJ-mediated chang e in viral envelope N-glycan composition inhibits HIV entry at the lev el of post-CD4 binding, the exact mechanism of inhibition remains to b e established. In this study we have examined the effects of NB-DNJ on virion envelope composition and CD4-induced gp120 shedding and gp41 e xposure. Virion composition analysis revealed an NB-DNJ-mediated reduc tion of 15% in overall virion envelope glycoprotein content and a redu ction of 26% in the proteolytic maturation of virion gp160. Taken toge ther, these two effects resulted in a reduction of approximately 40% i n virion gp120 content, CD4-induced shedding of gp120 from the surface s of envelope-transfected Cos cells was undetectable when gp120 was ex pressed in the presence of NB-DNJ. Similarly, the shedding of virion-a ssociated gp120 was reduced 7.4-fold, CD4-induced exposure of cryptic gp41 epitopes on the surfaces of HIV-expressing ACH-2 cells was also g reatly impaired, and the exposure of virion-associated gp41 epitopes w as reduced 4.0-fold, Finally, CD4-induced increases in the binding of antibodies to the V3 loop of ACH-2-cell expressed envelope glycoprotei ns were reduced 25-fold when the glycoproteins were expressed in the p resence of NB-DNJ. These results suggest that the NB-DNJ-mediated rete ntion of glycosylated N-glycans inhibits HIV entry by a combined effec t of a reduction in virion gp120 content and a qualitative defect with in the remaining gp120, preventing it from undergoing conformational c hanges after CD4 binding.