Cell surface expression of immature H glycoprotein in measles virus-infected cells

Two forms of hemagglutinin (H) protein, one with an apparent molecular mass of 78 kDa (78K H protein) and the other with that of 74 kDa (74K H protein ), are present in cells infected with measles virus (MV). We previously obs erved that only the mature 78K H protein, a completely glycosylated form of the 74K H protein, was expressed on the cell surface of the infected cells . In the present study, we detected transient expression of the 74K H prote in on the cell surface of infected cells by pulse-chase studies, although t he level of this expression was much lower than that of the 78K H protein. On the cell surface the 74K H protein was present as dimers and sensitive t o endo-beta-N-acetylglucosaminidase H digestion. Treatment with brefeldin A , which blocks the transport of membrane and secretory proteins from the en doplasmic reticulum to the Golgi apparatus, inhibited the cell surface expr ession of the 78K H protein, but not that of the 74K H protein. These data suggest that a part of the MV 74K H proteins could be transported directly to the cell surface - probably via an alternative pathway - without process ing to the complex form in the Golgi apparatus. (C) 2000 Elsevier Science B .V. All rights reserved.