STAT1 Regulates Lipopolysaccharide- and TNF-α-Dependent Expression of Transporter Associated with Antigen Processing 1 and Low Molecular Mass Polypeptide 2 Genes in Macrophages by Distinct Mechanisms

Transporter associated with Ag processing 1 and low molecular mass polypeptide 2 (LMP2) are essential for class I MHC function and share a common bidirectional promoter. In murine bone marrow-derived macrophages, LPS and TNF-α induced Tap1 and up-regulated Lmp2, which is constitutively expressed at low levels. These two genes are induced by LPS and TNF-α with distinct kinetics, at 6 and 12–24 h, respectively. Using macrophages derived from the TNF-α receptors of knockout mice, we found that induction by LPS is not due to the autocrine production of TNF-α. In macrophages from STAT-1 knockout mice, neither LPS nor TNF-α induced the expression of Tap1 or Lmp2. The shared promoter contains several areas that can be controlled by STAT-1, such as the proximal and distal IFN-γ activation site (GAS) boxes in the direction of the Tap1 gene. By making deletions of the promoter, we determined that only the proximal GAS box is required for LPS induction of Tap1 and Lmp2. In contrast, TNF-α induction of these two genes is dependent on the IFN regulatory factor-1 and NF-κB boxes, and not on the GAS box. Our experiments using gel shift analysis and Abs indicated that STAT1 binds to the GAS box in nuclear extracts from LPS-treated macrophages. The nuclear extracts obtained from macrophages treated with TNF-α bound to the IFN regulatory factor-1 and NF-κB boxes. These results show that LPS and TNF-α regulate the induction of Tap1 and Lmp2 through STAT1, but use distinct areas of the promoter.