JEM-1, a novel nuclear co-factor: localisation and functional interaction with AP-1.
JEM-1 is a novel gene whose mRNA expression in acute promyelocytic leukemia (APL) is induced by retinoid treatments. The gene product, a 45 kDa basic nuclear factor containing a leucine repeat, was transiently expressed in HeLa or COS-7 cells and immunocharacterized within the nuclei in fine punctuated structures which increase in size after cell transfection. Jem-1 was not expressed in the nucleoli. Experimental deletion of peptide domains of Jem-1 (JemDelta331-400 and Jem DeltaL179-206) showed that its C-terminal sequence (Thr331 --> Leu400) is required for nuclear translocation, while the leucine repeat domain (Arg179 --> Glu206) has no influence on subcellular localization. The Jem-1 protein was not detected in the PML-containing nuclear bodies or in speckled structures containing the splicing factor SC-35. In contrast it was localized in the nucleus in structures containing activator protein-1 (AP-1). DNA mobility shift assays showed that the in vitro translated Jem protein interacts neither with the DNA binding site of AP-1, nor directly with in vitro co-translated c-Fos or/and c-Jun proteins bound to this specific sequence. Interestingly, Jem-1-1 increased substantially the transcriptional activity of c-Jun (three-fold) and more strongly that of ectopically co-expressed c-Fos and c-Jun (five- to six-fold), as measured by a CAT reporter gene driven by a heterologous promoter containing the AP-1 binding site of the human collagenase gene. These synergistic effects were strongly Jem-1 dose-dependent. However, Jem-1 alone showed no activity on the collagenase promoter. A deletion of the leucine repeat of Jem-1 (Arg179 --> Glu206) did not diminish the enhancer capacity of Jem-1 on AP-1 activity. In contrast, the enhanced AP-1 activity was abrogated when Jem-1 was deleted of its C-terminus (Thr331 --> Leu400). We conclude that the 45 kDa nuclear product of the JEM-1 gene has features of a novel transcription cofactor, which is enhancing AP-1 activity without directly interacting with c-Jun or c-Fos proteins. Possible implications of these findings for APL cell maturation are discussed.
Tong
J H
JH
Institut National de la Santé et de la Recherche Médicale, INSERM-U496, Institut Universitaire d'Hématologie, Centre G Hayem, Hôpital Saint-Louis, F-75475 Paris, France.
Duprez
E
E
Lanotte
M
M
D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D019556:COS Cells; D002467:Cell Nucleus / Q000737:chemistry*; D006367:HeLa Cells; D006801:Humans; D009687:Nuclear Proteins / Q000032:analysis* / Q000235:genetics / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000502:physiology*; D014157:Transcription Factors / Q000032:analysis* / Q000235:genetics / Q000502:physiology
C105528:BLZF1 protein, human; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D009687:Nuclear Proteins; D018808:Transcription Factor AP-1; D014157:Transcription Factors