Interleukin-3 Stimulation of mcl-1 Gene Transcription Involves Activation of the PU.1 Transcription Factor through a p38 Mitogen-Activated Protein Kinase-Dependent Pathway

Institute of Molecular Biology, Academia Sinica, 128 Yen-Jiou Yuan Road, Section 2, Nankang, Taipei 11529, Taiwan, Republic of China.
Molecular and Cellular Biology (Impact Factor: 4.78). 04/2003; 23(6):1896-909. DOI: 10.1128/MCB.23.6.1896-1909.2003
Source: PubMed


We have previously demonstrated that the antiapoptotic gene mcl-1 is activated by interleukin-3 (IL-3) in Ba/F3 pro-B cells through two promoter elements designated the CRE-2 and SIE motifs.
While the CRE-2-binding complex contains the CREB protein and is activated by IL-3 through the phosphatidylinositol 3-kinase/Akt-dependent
pathway, the identity and cytokine activation pathway of the SIE-binding complex remains unclear. In this report, we demonstrated
that PU.1 is one component of the SIE-binding complex. A chromatin immunoprecipitation assay further confirmed that PU.1 binds
to the mcl-1 promoter region containing the SIE motif in vivo. While IL-3 stimulation does not significantly alter the SIE-binding activity
of PU.1, it markedly increases PU.1's transactivation activity. The latter effect coincides with the increased phosphorylation
of PU.1 following IL-3 activation of a p38 mitogen-activated protein kinase (p38MAPK)-dependent pathway. A serine-to-alanine substitution at position 142 significantly weakens PU.1's ability to be phosphorylated
by the p38MAPK immunocomplex. Furthermore, this S142A mutant is impaired in the ability to be further stimulated by IL-3 to transactivate
the mcl-1 reporter through the SIE motif. Taken together, our results demonstrate that IL-3 stimulation of mcl-1 gene transcription through the SIE motif involves phosphorylation of PU.1 at serine 142 by a p38MAPK-dependent pathway.

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