N. Lee et al., HLA-E SURFACE EXPRESSION DEPENDS ON BINDING OF TAP-DEPENDENT PEPTIDESDERIVED FROM CERTAIN HLA CLASS-I SIGNAL SEQUENCES, The Journal of immunology, 160(10), 1998, pp. 4951-4960
Previous studies showed that HLA-E was expressed in lymphoblastoid cel
l line (LCL) 721.221 cells, but surface expression was lacking. To det
ermine the signals controlling surface expression, we constructed a se
ries of hybrid genes using complementary portions derived from the HLA
-E and HLA-A2 genes. In this manner, a hybrid of HLA-E was identified,
designated AEH, which differed from HLA-E by having the HLA-AZ signal
sequence substituting for the HLA-E leader peptide. Transfection of L
CL 721.221 cells,vith AEH induced HLA-E surface expression. Analysis o
f peptides bound to HLA-E revealed that a nonamer peptide derived from
the A2 signal sequence was the predominant peptide bound. LCL 721.221
cells transfected with certain class I genes, including HLA-G, were a
lso sufficient to promote peptide binding and HLA-E surface expression
without increasing the level of HLA-E heavy chain synthesis, Peptides
bound to HLA-E consisted of nine amino acids, with methionine at posi
tion 2 and leucine in the carboxyl-terminal position, and were nearly
identical to the leader sequence-derived peptide previously shown to b
e a predominant peptide bound to the murine Qa-l Ag, Signal peptides d
erived from certain HLA-B proteins with threonine in position 2 only m
arginally up-regulated FILA-E surface expression in .221 cells, An exa
mination of HLA-E peptide binding in the TAP negative cell line .134 i
ndicated that peptide binding to HLA-E was dependent on a functional T
AP heterodimer regardless of whether peptide was available in cis, as
in the AEH construct, or in trans, as in the class I transfectants of
.221 cells.