CELL-SURFACE LOCALIZATION OF THE 78 KD GLUCOSE-REGULATED PROTEIN (GRP-78) INDUCED BY THAPSIGARGIN

In the present study it was found that the synthesis of the 78 kD gluc ose-regulated protein (GRP 78 or BIP) is vigorously induced in human r abdomiosarcoma cells (TE 671/RD) following both short-term (1 h) and p rolonged (18 h) exposure to 100 nM thapsigargin (Tg). Flow cytometric analysis with a specific anti-GRP 78 polyclonal antibody showed that T g-treated cells express the GRP 78 on the plasma membrane. Cell surfac e localization of the Tg-induced GRP 78 was confirmed by biotinylation of membrane-exposed proteins and subsequent isolation of the biotin-l abelled proteins by streptavidin/agarose affinity chromatography. It w as found that a fraction of the Tg-induced GRP 78 is present among the biotin-labelled, surface-exposed, proteins. Conversely, the GRP 78 im munoprecipitated from unfractionated lysates of Tg-treated and biotin- reacted cells was found to be biotinylated. This is the first report d emonstrating surface expression of GRP 78 in cells exposed to a specif ic GRP 78-inducing stimulus.