ABERRANT TRAFFICKING OF HEPATITIS-B VIRUS GLYCOPROTEINS IN CELLS IN WHICH N-GLYCAN PROCESSING IS INHIBITED

The role of N-glycan trimming in glycoprotein fate and function is unc lear. We have recently shown that hepatitis B virus (HBV) DNA is not e fficiently secreted from cells in which alpha-glucosidase mediated N-g lycan trimming is inhibited. Here it is shown that, in cells in glucos idase-inhibited cells, viral DNA, accompanied by envelope and core pro teins, most likely accumulate within lysosomal compartments. Pulse-cha se experiments show that although the viral glycoproteins (L, M, and S ) are dysfunctional, in the sense that they do not mediate virion egre ss and are not efficiently secreted from the cell, they all still leav e the endoplasmic reticulum (ER). Surprisingly, however, the glycoprot eins retained within the cell were not rapidly degraded, appearing as aggregates, enriched for L and M, with intracellular half-lives exceed ing 20 h. Moreover, by 24 h after synthesis, a substantial fraction of the detained glycoproteins appeared to return to the ER, although a c onsiderable amount was also found in the lysosomes. To our knowledge, this is the first report that shows, as a consequence of inhibiting gl ycosylation processing, certain glycoproteins (i) become dysfunctional and aggregate, yet still depart from the ER, and (ii) have extended r ather than shortened half-lives. Taken together, these data suggest th at proper intracellular routing of HBV glycoproteins requires ER gluco sidase function. It is hypothesized that failure to process N-glycan c auses HBV glycoproteins to aggregate and that impaired protein-protein interactions and trafficking are the result of misfolding.