JEM-1, a novel nuclear co-factor: localisation and functional interaction with AP-1

Area of Science:

• Molecular Biology
• Cell Biology
• Cancer Research

Background:

• The JEM-1 gene's mRNA expression is induced by retinoid treatments in acute promyelocytic leukemia (APL).
• JEM-1 encodes a 45 kDa basic nuclear factor with a leucine repeat domain.

Purpose of the Study:

• To characterize the JEM-1 protein's subcellular localization and its role in transcriptional regulation.
• To investigate JEM-1's interaction with activator protein-1 (AP-1) and its components (c-Fos, c-Jun).

Main Methods:

• Transient expression in HeLa or COS-7 cells for immunocharacterization.
• Experimental deletion of JEM-1 domains to assess nuclear translocation and cofactor activity.
• DNA mobility shift assays to evaluate protein-DNA and protein-protein interactions.
• CAT reporter gene assays to measure transcriptional activity on an AP-1-driven promoter.

Main Results:

• JEM-1 localizes to the nucleus in structures associated with AP-1, but not PML or SC-35.
• The C-terminal sequence of JEM-1 is essential for nuclear translocation; the leucine repeat domain is not.
• JEM-1 directly interacts with neither AP-1 DNA binding sites nor c-Fos/c-Jun proteins.
• JEM-1 significantly enhances AP-1 transcriptional activity in a dose-dependent manner, particularly when co-expressed with c-Fos and c-Jun.
• The C-terminus of JEM-1 is required for its enhancer function, while the leucine repeat is not.

Conclusions:

• JEM-1 functions as a novel transcription cofactor that enhances AP-1 activity without direct interaction with c-Fos or c-Jun.
• The C-terminal domain of JEM-1 is critical for its nuclear localization and cofactor function.
• These findings suggest a role for JEM-1 in retinoid-induced APL cell maturation.