Mucosa-Specific Targets for Regulation of IFN-γ Expression: Lamina Propria T Cells Use Different cis- Elements than Peripheral Blood T Cells to Regulate Transactivation of IFN-γ Expression

Abstract

Activation of lamina propria (LP) T cells via the CD2 pathway enhances IFN-γ (IFN-γ) secretion with further enhancement after CD28 coligation. The molecular mechanisms regulating IFN-γ expression in LP T cells remain unknown. Previous studies in PBL and T cell lines identified cis- and trans-regulatory elements in TCR-mediated expression of IFN-γ. This study examines CD2 and PMA/ionophore-responsive IFN-γ promoter elements. Activation of LPMC via CD2-induced IFN-γ secretion and a parallel up-regulation of mRNA expression. CD28 coligation enhanced mRNA stability without up-regulating transcription as measured by nuclear run-on. Transfection of a −2.7-kb IFN-γ promoter-reporter construct into PBL and LP mononuclear cells (LPMC) revealed significant promoter activity after CD2 activation, with additional transactivation after CD2/CD28 costimulation in PBL, but not in LPMC. Functional analysis using truncated promoter fragments identified distinct cis-regulatory regions selectively transactivating IFN-γ expression in PBL compared with LPMC. In PBL, CD2 activation elements reside within the −108- to +64-bp region. However, in LPMC the upstream region between −204 and −108 bp was essential. Transfection of the proximal and distal AP-1-binding elements, as well as TRE/AP-1 constructs, revealed functional activation of AP-1 subsequent to CD2 signaling, with activation critical in PBL but diminished in LPMC. Electromobility shift analysis using oligonucleotides encompassing the proximal, distal, and BED/AP-1-binding regions failed to demonstrate selective transactivation after CD2 signaling of LPMC. This report provides evidence that activation of LPMC results in transactivation of multiple promoter elements regulating IFN-γ expression distinct from those in PBL.