PU.1-c-Jun interaction is crucial for PU.1 function in myeloid development

Area of Science:

• Molecular Biology
• Hematopoiesis
• Transcription Factors

Background:

• The Ets transcription factor PU.1 is essential for monocyte, macrophage, and B cell differentiation.
• PU.1 regulates hematopoietic differentiation through interactions with other transcription factors, including C/EBPα and c-Jun.
• PU.1 can recruit c-Jun to promoters lacking AP-1 binding sites.

Purpose of the Study:

• To investigate the functional importance of the PU.1-c-Jun interaction in hematopoietic differentiation.
• To determine if the physical interaction between PU.1 and c-Jun is essential for PU.1's role in myeloid commitment.

Main Methods:

• Generation of PU.1 point mutants unable to bind c-Jun but retaining DNA binding affinity.
• Assay of PU.1 mutant transactivation of a reporter gene requiring PU.1-c-Jun interaction.
• Assessment of monocyte/macrophage differentiation in PU.1-deficient cells expressing PU.1 mutants.
• Analysis of hematopoiesis and survival in knock-in mice carrying PU.1 point mutations.

Main Results:

• PU.1 mutants failed to transactivate reporter genes dependent on the PU.1-c-Jun interaction.
• PU.1 mutants could not induce monocyte/macrophage differentiation in PU.1-deficient cells.
• Knock-in mice with PU.1 mutations exhibited a severe block in hematopoiesis and perinatal lethality.
• Myeloid differentiation was blocked in PU.1 mutant mice, leading to a loss of mature hematopoietic cells.
• Restoration of macrophage differentiation was achieved by fusing PU.1 mutants to c-Jun.

Conclusions:

• A physical interaction between PU.1 and c-Jun is critical for PU.1's function in myeloid differentiation.
• The PU.1-c-Jun interaction is essential for the transactivation of target genes required for myeloid commitment.
• Disruption of the PU.1-c-Jun interaction leads to severe hematopoiesis defects and lethality in vivo.