Direct role of NF-kappaB activation in Toll-like receptor-triggered HLA-DRA expression

Area of Science:

• Immunology
• Molecular Biology
• Cell Biology

Background:

• Microbial components, including CpG-DNA and LPS, activate Toll-like receptors (TLRs) to induce cell surface MHC class II (MHC-II) expression.
• MHC-II molecules are critical for antigen presentation and T-cell activation in adaptive immunity.

Purpose of the Study:

• To investigate the molecular mechanisms underlying CpG-DNA and LPS-induced HLA-DRA expression in human B cells.
• To determine the roles of CIITA and NF-kappaB in TLR-mediated MHC-II expression.

Main Methods:

• Utilized a human B cell line (RPMI 8226).
• Employed ectopic expression of dominant-negative CIITA mutant and CIITA-targeted RNA interference.
• Performed electrophoretic mobility shift assays (EMSAs) and chromatin immunoprecipitation (ChIP) assays.
• Analyzed nuclear factor-kappaB (NF-kappaB) activation and its interaction with the HLA-DRA promoter.

Main Results:

• CpG-DNA and LPS induced HLA-DRA expression in RPMI 8226 cells.
• CIITA activation alone was insufficient for maximal MHC-II expression induced by CpG-DNA and LPS.
• NF-kappaB activation was essential for CpG-DNA and LPS-induced HLA-DRA expression, unlike IFN-gamma-induced expression which relies on CIITA.
• Functional interaction of NF-kappaB with the HLA-DRA promoter was necessary for TLR-mediated induction.

Conclusions:

• TLR-mediated induction of HLA-DRA by CpG-DNA and LPS requires both CIITA activation and NF-kappaB binding to the promoter.
• This pathway reveals a novel regulatory mechanism for MHC-II gene expression, highlighting complexity and functional diversity in immune signaling.