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Stat4, a novel gamma interferon activation site-binding protein expressed in early myeloid differentiation
K Yamamoto1, F W Quelle, W E Thierfelder
1Department of Biochemistry, St. Jude Children's Research Hospital, Memphis, Tennessee 38105.
Abstract:
Interferon regulation of gene expression is dependent on the tyrosine phosphorylation and activation of the DNA-binding activity of two related proteins of 91 kDa (STAT1) and/or 113 kDa (STAT2). Recent studies have suggested that these proteins are substrates of Janus kinases and that proteins related in STAT1 are involved in a number of signalling pathways, including those activated in myeloid cells by erythropoietin and interleukin-3 (IL-3). To clone STAT-related proteins from myeloid cells, degenerate oligonucleotides were used in PCRs to identify novel family members expressed in myeloid cells. This approach allowed the identification and cloning of the Stat4 gene, which is 52% identical to STAT1. Unlike STAT1, Stat4 expression is restricted but includes myeloid cells and spermatogonia. In the erythroid lineage, Stat4 expression is differentially regulated during differentiation. Functionally, Stat4 has the properties of other STAT family genes. In particular, cotransfection of expression constructs for Stat4 and Jak1 and Jak2 results in the tyrosine phosphorylation of Stat4 and the acquisition of the ability to bind to the gamma interferon (IFN-gamma)-activated sequence of the interferon regulatory factor 1 (IRF-1) gene. Stat4 is located on mouse chromosome 1 and is tightly linked to the Stat1 gene, suggesting that the genes arose by gene duplication. Unlike Stat1, neither IFN-alpha nor IFN-gamma activates Stat4. Nor is Stat4 activated in myeloid cells by a number of cytokines, including erythropoietin, IL-3, granulocyte colony-stimulating factor, stem cell factor, colon-stimulating factor 1, hepatocyte growth factor, IL-2, IL-4, and IL-6.
Insights
Researchers identified a new STAT family gene, Stat4, in myeloid cells. Stat4 is activated by Janus kinases and binds DNA, similar to STAT1, but has a distinct expression pattern and is not activated by interferons.
Area of Science:
- Molecular Biology
- Cell Signaling
- Immunology
Background:
- Interferon signaling involves STAT1 and STAT2 proteins, activated by Janus kinases.
- STAT proteins regulate gene expression through tyrosine phosphorylation and DNA binding.
- Understanding STAT family diversity is crucial for deciphering cellular signaling pathways.
Purpose of the Study:
- To identify novel STAT-related proteins in myeloid cells.
- To characterize the function and regulation of a newly discovered STAT family member.
Main Methods:
- Polymerase chain reaction (PCR) with degenerate oligonucleotides.
- Gene cloning and sequencing.
- Cotransfection assays with expression constructs.
- Analysis of gene expression patterns.
Main Results:
- Identified and cloned the Stat4 gene, 52% identical to STAT1.
- Stat4 is expressed in myeloid cells and spermatogonia, with differential regulation in erythroid lineage.
- Stat4 undergoes tyrosine phosphorylation by Jak1/Jak2 and binds to the IFN-gamma-activated sequence of the IRF-1 gene.
- Stat4 is not activated by interferons (IFN-alpha, IFN-gamma) or various cytokines tested.
Conclusions:
- Stat4 is a novel STAT family member with distinct expression and activation properties compared to STAT1.
- Stat4's phosphorylation and DNA-binding capabilities suggest a role in cytokine signaling pathways.
- The close linkage of Stat4 and Stat1 on mouse chromosome 1 suggests a shared evolutionary origin through gene duplication.