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Inhibition of ornithine decarboxylase induces STAT3 tyrosine phosphorylation and DNA binding in IEC-6 cells
L M Pfeffer1, C H Yang, S R Pfeffer
1Department of Pathology, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA. lpfeffer@utmem.edu
Abstract:
Polyamines are required for the proliferation of the rat intestinal mucosal IEC-6 cell line. Ornithine decarboxylase (ODC) is the enzyme that catalyzes the first step in polyamine synthesis. ODC inhibition not only leads to polyamine depletion but also leads to inhibition of cell proliferation and regulates the expression of the immediate-early genes c-fos, c-myc, and c-jun. Members of the signal transducers and activators of transcription (STAT) transcription factor family bind to the sis-inducible element (SIE) present in the promoters to regulate the expression of a variety of important genes. In the present study, we tested the hypothesis that the STAT3 transcription factor, which is responsible for activation of the acute phase response genes, is activated after inhibition of ODC. We found that inhibition of ODC rapidly induces STAT3 activation as determined by STAT3 tyrosine phosphorylation, translocation of STAT3 from the cytoplasm into the nucleus, and the presence of STAT3 in SIE-dependent DNA-protein complexes. STAT3 activation upon inhibition of ODC was accompanied by the activation of a STAT3-dependent reporter construct. Moreover, prolonged polyamine depletion resulted in downregulation of cellular STAT3 levels.
Insights
Inhibiting ornithine decarboxylase (ODC) rapidly activates STAT3 signaling in rat intestinal cells. Prolonged polyamine depletion, however, leads to a decrease in cellular STAT3 levels.
Area of Science:
- Cell Biology
- Molecular Biology
- Biochemistry
Background:
- Polyamines are essential for cell proliferation, particularly in the rat intestinal mucosal IEC-6 cell line.
- Ornithine decarboxylase (ODC) is the key enzyme in polyamine synthesis, and its inhibition impacts cell growth and gene expression.
- Signal transducers and activators of transcription (STAT) proteins regulate gene expression by binding to specific DNA elements.
Purpose of the Study:
- To investigate the hypothesis that STAT3 transcription factor is activated following ODC inhibition.
- To elucidate the role of STAT3 in cellular responses to polyamine depletion.
Main Methods:
- Inhibition of ODC in IEC-6 cells.
- Assessment of STAT3 activation through tyrosine phosphorylation and nuclear translocation.
- Analysis of STAT3 binding to sis-inducible elements (SIE).
- Utilizing a STAT3-dependent reporter construct.
Main Results:
- ODC inhibition rapidly induced STAT3 activation, evidenced by increased tyrosine phosphorylation and nuclear translocation.
- Activated STAT3 formed complexes with SIE in DNA.
- STAT3 activation correlated with the activation of a STAT3-dependent reporter construct.
- Extended polyamine depletion led to reduced cellular STAT3 levels.
Conclusions:
- ODC inhibition triggers rapid STAT3 activation in IEC-6 cells.
- STAT3 plays a role in the cellular response to ODC inhibition and polyamine depletion.
- The findings suggest a complex regulatory relationship between polyamine synthesis and STAT3 signaling.