INTERFERON-GAMMA INDUCTION OF THE HUMAN-LEUKOCYTE ANTIGEN-E GENE IS MEDIATED THROUGH BINDING OF A COMPLEX CONTAINING STAT1-ALPHA TO A DISTINCT INTERFERON-GAMMA-RESPONSIVE ELEMENT
Ks. Gustafson et Gd. Ginder, INTERFERON-GAMMA INDUCTION OF THE HUMAN-LEUKOCYTE ANTIGEN-E GENE IS MEDIATED THROUGH BINDING OF A COMPLEX CONTAINING STAT1-ALPHA TO A DISTINCT INTERFERON-GAMMA-RESPONSIVE ELEMENT, The Journal of biological chemistry, 271(33), 1996, pp. 20035-20046
Expression of the human major histocompatibility complex (MHC) class I
genes has been shown previously to increase at the transcriptional le
vel following exposure to interferon-gamma (IFN-gamma). In this report
we have examined the molecular mechanisms involved in the IFN gamma-i
nduced transcription of the human MHC class I gene, HLA-E. Functional
analysis of CAT reporter gene constructs under the control of the HLA-
E promoter transfected into U937 cells revealed the presence of a dist
inct IFN-gamma-responsive element, termed the interferon response regi
on (IRR), that was necessary and sufficient to mediate the response to
IFN-gamma. This cis-acting regulatory sequence contains an imperfect
inverted repeat; the 5'-half of the IRR resembles the IFN-gamma activa
tion site (GAS), and the 3'-half of the IRR resembles the interferon-s
timulated response element (ISRE). Gel mobility shift assays demonstra
ted that the IRR bound a single, specific, IFN-gamma-induced complex (
IRR-AC), which was formed rapidly following treatment with IFN-gamma a
nd was independent of protein synthesis. Competition experiments with
GAS and ISRE sequences from other IFN-inducible genes showed that GAS
sequences competed for the IRR-AC, whereas ISRE sequences did not comp
ete. Mutational analysis demonstrated that point mutations in either t
he 5'-half or 3'-half of the IRR prevented binding of the complex and
abrogated or markedly reduced the IFN-gamma responsiveness of reporter
gene constructs. Supershift analysis revealed that the IRR-AC contain
s a factor that was recognized by antibodies specific for the protein
STAT1 alpha (signal transducer and activator of transcription). Taken
together, these findings suggest that the mechanism of IFN-gamma-induc
ed transcription of the HLA-E gene is distinct from that of other MHC
class I genes.