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CIITA stimulation of transcription factor binding to major histocompatibility complex class II and associated
K L Wright1, K C Chin, M Linhoff
1Lineberger Comprehensive Cancer Center and the Department of Immunology and Microbiology, University of North Carolina, Chapel Hill, NC 27599, USA.
Insights
The CIITA protein is essential for activating major histocompatibility complex class II genes, crucial for immune responses. It functions by assembling transcription factors, not direct DNA binding, suggesting a novel transactivator role.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- The CIITA protein is a master transactivator of major histocompatibility complex class II (MHC-II) genes, critical for antigen presentation and immune function.
- Defects in CIITA lead to severe immunodeficiencies, highlighting its crucial role in the immune system.
- CIITA controls the induction of MHC-II genes by interferon-gamma but does not directly bind DNA.
Purpose of the Study:
- To investigate the mechanism by which CIITA activates MHC-II gene transcription.
- To determine the role of CIITA in the assembly of transcription factor complexes on MHC-II gene promoters.
- To identify functional domains within the CIITA protein responsible for transactivation and promoter binding.
Main Methods:
- Expression of CIITA in CIITA-deficient G3A cells.
- In vivo genomic footprinting to assess transcription factor binding.
- Dissection of the CIITA protein to analyze functional domains.
Main Results:
- CIITA is required for the assembly of transcription factor complexes on the promoters of MHC-II family genes (DRA, Ii, DMB).
- CIITA-dependent promoter assembly occurs in interferon-gamma-inducible cells but not in B lymphocytes.
- Transactivation and promoter loading functions of CIITA are inseparable and depend on a GTP binding motif.
Conclusions:
- CIITA acts as a scaffold, facilitating the assembly of transcription factors at MHC-II gene promoters.
- The findings suggest CIITA represents a new class of transcriptional activator.
- Understanding CIITA's mechanism is vital for addressing immunodeficiencies related to MHC-II regulation.
Abstract:
CIITA is a master transactivator of the major histocompatibility complex class II genes, which are involved in antigen presentation. Defects in CIITA result in fatal immunodeficiencies. CIITA activation is also the control point for the induction of major histocompatibility complex class II and associated genes by interferon-gamma, but CIITA does not bind directly to DNA. Expression of CIITA in G3A cells, which lack endogenous CIITA, followed by in vivo genomic footprinting, now reveals that CIITA is required for the assembly of transcription factor complexes on the promoters of this gene family, including DRA, Ii, and DMB. CIITA-dependent promoter assembly occurs in interferon-gamma-inducible cell types, but not in B lymphocytes. Dissection of the CIITA protein indicates that transactivation and promoter loading are inseparable and reveal a requirement for a GTP binding motif. These findings suggest that CIITA may be a new class of transactivator.