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Bcr/Abl activates transcription of the Bcl-X gene through STAT5
1Department of Adult Oncology, Dana Farber Cancer Institute, Department of Adult Oncology, Boston, MA 02115, USA.
Abstract:
Several tyrosine kinase oncogenes have been associated with myeloproliferative diseases, including Bcr/Abl, Tel/Abl, Tel/Jak2, and Tel/PDGFR. One target molecule shared by these oncogenes is known to be STAT5. We generated sublines of Ba/F3 cells in which either wild-type STAT5 or a constitutively active mutant of STAT5 (STAT5-1*6) were expressed under the control of a tetracycline-inducible promoter. These cell lines were compared with a Ba/F3 cell line in which the expression of p210(Bcr/Abl) was made inducible by a similar promoter. Before induction, all cells were dependent on interleukin 3 (IL-3) for growth and survival. Both STAT5-1*6 and Bcr/Abl enhanced viability and induced proliferation in the absence of IL-3. We found that the proviability protein Bcl-X(L), but not Bcl-2, was induced by both p210(Bcr/Abl) and STAT5-1*6. Using a Bcl-X gene promoter construct fused to a luciferase complementary DNA (cDNA), both p210(Bcr/Abl) and STAT5-1*6 were shown to induce transcription of Bcl-X. The increase in transcription of the Bcl-X promoter and the increase in Bcl-X protein, due to p210(Bcr/Abl), were blocked by expression of a dominant negative STAT5 mutant. Interestingly, however, STAT5-1*6 required the continued presence of IL-3 to cause a significant increase in Bcl-X(L) protein, whereas p210(Bcr/Abl) did not need IL-3. Studies with enzyme inhibitors suggest that the extra signal supplied by IL-3 may be supplied by the PI3K pathway. Overall, these data suggest that constitutively activated STAT5 can increase viability and proliferation of Ba/F3 cells. This may contribute to, but is not likely sufficient for, the enhanced viability associated with Bcr/Abl transformation.
Insights
Constitutively activated STAT5 (Signal Transducer and Activator of Transcription 5) enhances cell viability and proliferation, partly by inducing the Bcl-X(L) protein. However, STAT5 activation alone may not be sufficient for Bcr/Abl-driven transformation in myeloproliferative diseases.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- Tyrosine kinase oncogenes like Bcr/Abl are implicated in myeloproliferative diseases.
- STAT5 is a key downstream target molecule for several oncogenic tyrosine kinases.
Purpose of the Study:
- To investigate the role of constitutively active STAT5 in cell viability and proliferation.
- To determine if STAT5 activation is sufficient for Bcr/Abl-mediated transformation.
Main Methods:
- Generated Ba/F3 cell lines with inducible wild-type or mutant STAT5 (STAT5-1*6) or p210(Bcr/Abl) expression.
- Assessed cell growth, viability, and Bcl-X(L) protein levels with and without interleukin-3 (IL-3).
- Utilized a luciferase reporter assay to measure Bcl-X gene transcription.
Main Results:
- Both STAT5-1*6 and p210(Bcr/Abl) induced cell proliferation and viability independently of IL-3.
- Both oncogenes upregulated the proviability protein Bcl-X(L) and induced Bcl-X gene transcription.
- STAT5-1*6 required IL-3 for significant Bcl-X(L) induction, unlike p210(Bcr/Abl), suggesting PI3K pathway involvement.
Conclusions:
- Constitutively active STAT5 enhances Ba/F3 cell viability and proliferation.
- STAT5 activation contributes to, but is likely insufficient for, Bcr/Abl-driven transformation.
- STAT5's role in Bcl-X(L) induction may be modulated by IL-3 and the PI3K pathway.