BREFELDIN A-INDUCED ALTERATIONS IN PROCESSING OF MHC CLASS II-II COMPLEX DEPEND UPON MICROTUBULAR FUNCTION

The role of microtubules in the brefeldin A (BFA)-associated relocatio n of major histocompatibility complex (MHC) class II alpha beta chains (alpha beta) and the invariant chain (li) was characterized in Rail c ells by the use of nocodazole (ND), BFA blocked the transport of alpha Bli proteins through the Golgi and redistributed them to the endoplas mic reticulum (ER) along with Golgi-resident enzymes, The result of th e colocalization of processing enzymes and newly synthesized proteins was a downshift of alpha beta li molecular weight (MW) of 2 kDa, and t heir resistance to endoglycosidase H (endo H) after 6 hr of chase. ND by itself had no effect on the processing and transport of ap to the c ell surface, The addition of ND to BFA-treated cells downshifted alpha beta li by 4 kDa, Additionally, alpha beta li proteins remained sensi tive to neuraminidase after 16 hr of chase, In vitro alpha-mannosidase treatment of immunoprecipitated alpha beta li generated a similar 4-k Da downshift of MW, Either 1-deoxymannojirimycin (DJN) or swainsonine (SWN) blocked the MW downshift caused by BFA + ND treatment, These obs ervations indicated that in Rail cells, most of the BFA-associated rel ocations of cis-, medial Golgi proteins, and the addition of sialic ac id from the trans-Golgi were microtubule-independent. The retrograde t ransport of the medial Golgi enzyme N-acetylglucosamine transferase, h owever, required microtubular function, Microtubule disrupters could a ffect BFA treatment of viral infections by further disrupting viral pr otein processing. (C) 1997 Wiley-Liss, Inc.