Interferon-gamma- and phorbol myristate acetate-responsive elements involved in intercellular adhesion molecule-1...

Area of Science:

• Molecular Biology
• Immunology
• Cell Biology

Background:

• Interferon-gamma (IFN-γ) and phorbol myristate acetate (PMA) induce intercellular adhesion molecule-1 (ICAM-1) mRNA upregulation.
• This upregulation occurs via stabilization of a labile ICAM-1 mRNA.
• The specific mRNA regions responsible for this regulation are not fully defined.

Purpose of the Study:

• To identify the specific regions within ICAM-1 mRNA that mediate responsiveness to IFN-γ and PMA.
• To elucidate the roles of these regions in mRNA destabilization and signal transduction.

Main Methods:

• Generation of ICAM-1 deletion mutants and stable transfection into murine fibroblast Ltk- cells.
• Analysis of ICAM-1 mRNA induction by IFN-γ and PMA in transfected cells.
• Construction of chimeric ICAM-2 reporter mRNAs containing ICAM-1 regions.
• mRNA half-life analysis to assess turnover rates.

Main Results:

• The region encoding the ICAM-1 cytoplasmic domain is essential for IFN-γ responsiveness and confers instability.
• The 3′-untranslated region (UTR) of ICAM-1 is required for PMA responsiveness and also confers instability.
• Chimeric ICAM-2 mRNAs demonstrated that the ICAM-1 cytoplasmic domain confers IFN-γ responsiveness, while the 3′-UTR confers PMA responsiveness.
• Induction of chimeric mRNAs by IFN-γ and PMA is partly due to prolonged turnover rates.

Conclusions:

• Two distinct regions in ICAM-1 mRNA regulate its stability and responsiveness to cytokines.
• The cytoplasmic domain mediates IFN-γ-induced stabilization.
• The 3′-UTR mediates PMA-induced stabilization.