Interferon-γ Induction of the Human Leukocyte Antigen-E Gene Is Mediated through Binding of a Complex Containing STAT1α to a Distinct Interferon-γ-responsive Element

Abstract

Expression of the human major histocompatibility complex (MHC) class I genes has been shown previously to increase at the transcriptional level following exposure to interferon-␥ (IFN-␥). In this report we have examined the molecular mechanisms involved in the IFN-␥-induced 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 distinct IFN-␥-responsive element, termed the interferon response region (IRR), that was necessary and sufficient to mediate the response to IFN-␥. This cis-acting regulatory sequence contains an imperfect inverted repeat; the 5-half of the IRR resembles the IFN-␥ activation site (GAS), and the 3-half of the IRR resembles the interferon-stimulated response element (ISRE). Gel mobility shift assays demonstrated that the IRR bound a single, specific, IFN-␥-induced complex (IRR-AC), which was formed rapidly following treatment with IFN-␥ and was independent of protein synthesis. Competition experiments with GAS and ISRE sequences from other IFNinducible genes showed that GAS sequences competed for the IRR-AC, whereas ISRE sequences did not compete. Mutational analysis demonstrated that point mutations in either the 5-half or 3-half of the IRR prevented binding of the complex and abrogated or markedly reduced the IFN-␥ responsiveness of reporter gene constructs. Supershift analysis revealed that the IRR-AC contains a factor that was recognized by antibodies specific for the protein STAT1␣ (signal transducer and activator of transcription). Taken together, these findings suggest that the mechanism of IFN-␥-induced transcription of the HLA-E gene is distinct from that of other MHC class I genes.

HLA-E upregulation on IFN-γ-activated AML blasts impairs CD94/NKG2A-dependent NK cytolysis after haplo-mismatched hematopoietic SCT

“…It was shown earlier that HLA-E is tightly upregulated on IFN-g-induced activation through STAT1a and GATA3 response elements. 18,19 We have shown a dose-dependent link between increased cell-surface expression of HLA-E on AML blast cells and IFN-g treatment. IFN-g has earlier been reported to protect ovarian carcinoma and melanoma cells from lysis through a CD94/NKG2A-dependent pathway.…”

“…18,19 Current concepts about its function focus essentially on its capacity to inhibit the activities of CD94/NKG2A-expressing NK cells. 20 As shown in Figure 3c, HLA-E expression increased significantly on IFN-g treatment of AML blasts.…”

A 3′-Transcribed Region of the HLA-A2 Gene Mediates Posttranscriptional Stimulation by IFN-γ

“…Other class I genes, such as HLA-B7 and the murine H-2L and H-2K genes, have been shown to have a functional ISRE region which, by itself, can mediate a strong transcriptional response to IFN-␥ most likely involving the Janus kinase (Jak)/Stat family of protein kinases (18,57). In addition, transcription of the class Ib gene HLA-E has been shown to be stimulated by IFN-␥ through a unique IFN response element, the interferon response region, through the Jak/Stat pathway (58). It is unclear whether the HLA-A locus genes are regulated by IFN-␥ posttranscriptionally through the Jak/Stat pathway.…”

A Specific Interferon (IFN)-stimulated Response Element of the Distal HLA-G Promoter Binds IFN-regulatory Factor 1 and Mediates Enhancement of This Nonclassical Class I Gene by IFN-β

“…The nonclassical HLA-E also contains a specific IFN-␥ response region constituted of two adjacent cis-acting regulatory elements, both of which are required to mediate the full response to IFN-␥ (48). No adjacent cooperative sequence seems to be required for full induction by IFN-␤ through the functional ISRE within the HLA-G promoter, which identifies the particular nature of IFN-␤-mediated HLA-G induction.…”