Raj. Mcilhinney et al., ASSEMBLY INTRACELLULAR TARGETING AND CELL-SURFACE EXPRESSION OF THE HUMAN N-METHYL-D-ASPARTATE RECEPTOR SUBUNITS NR1A AND NR2A IN TRANSFECTED CELLS, Neuropharmacology, 37(10-11), 1998, pp. 1355-1367
The intracellular trafficking, assembly, and cell surface targeting of
the human N-methyl-D-aspartate receptor subunits NR1a and NR2A has be
en studied using both transiently and permanently transfected mammalia
n cell lines. The expression of either NR1a or NR2A alone does not res
ult in significant cell surface expression of either subunit as determ
ined by cell surface biotinylation and immunofluorescence staining. Wh
en NR1a is expressed alone large intracellular accumulations of the su
bunit are formed which do not co-localize with the golgi apparatus mar
kers protein p58 and wheat germ agglutinin, but do co-localize with th
e endoplasmic reticulum marker calreticulin. Go-expression of NR1a and
NR2A results in a reduction of these intracellular accumulations and
the appearance of both subunits on the cell surface. Immunoprecipitati
on of NR1a from in vitro translated subunit proteins showed that NR2A
could only be immunoprecipitated with NR1a when both subunits were co-
synthesized in the presence of microsomes. When cells expressing NR1a
and NR2A were incubated with [S-35]methionine in the presence of Brefe
ldin-A, a drug which prevents protein transport from the endoplasmic r
eticulum, NR2A could be immunoprecipitated by an antiserum specific fo
r NR1a. Together these results suggest that the NMDA receptor subunits
are assembled in the endoplasmic reticulum and that co-synthesis of t
he subunits is necessary for their association and their successful ce
ll surface targeting. (C) 1998 Elsevier Science Ltd. All rights reserv
ed.