[Frontiers in Bioscience 14, 2944-2958, January 1, 2009]

The dark and the bright side of Stat3: proto-oncogene and tumor-suppressor

Andrea Ecker1, Olivia Simma2, Andrea Hoelbl2, Lukas Kenner3,4, Hartmut Beug1, Richard Moriggl3, Veronika Sexl2

1Institute of Molecular Pathology (IMP), Austria, 2Institute of Pharmacology, Medical University of Vienna (MUW), Austria,3Ludwig-Boltzmann-Institute for Cancer Research (LBI-CR), Austria, 4Institute of Clinical Pathology, Medical University of Vienna (MUW), Austria

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Materials and Methods
3.1. (3H) thymidine incorporation
3.2. Retroviral constructs
3.3. Tissue culture and retroviral infections of fibroblasts
3.4. Retroviral infection and bone marrow transplantation studies
3.5. Western Blot analysis
3.6. Fibroblast Focus formation assays
3.7. Colony formation assay in growth-factor free methylcellulose
3.8. Flow cytometric analysis (FACS)
3.9. Tumor formation in nu/nu mice
3.10. Gel shift assays (EMSAs)
3.11. Reverse transcription polymerase chain reaction (RT-PCR) and analysis of sex-determining region (SRY) expression
4.12. Mouse pathology, histology and immunohistochemistry
4.13. Statistical analysis
4. Results
4.1. Stat3alphaC expression blocks cell proliferation in murine fibroblasts
4.2. Stat3alphaC blocks c-myc induced transformation in primary murine fibroblasts
4.3. Stat3beta is constitutively active when expressed in fibroblasts
4.4. Constitutive active Stat3 (Stat3alphaC and Stat3beta) induces leukemia in mice
4.5. Histological analysis reveals highly aggressive T cell lymphoma/T cell leukemia
5. Discussion
6. Acknowledgments
7. References

1. ABSTRACT

Stat transcription factors have been implicated in tumorigenesis in mice and men. Stat3 and Stat5 are considered powerful proto-oncogenes, whereas Stat1 has been demonstrated to suppress tumor formation. We demonstrate here for the first time that a constitutive active version of Stat3alpha (Stat3alphaC) may also suppress transformation. Mouse embryonic fibroblasts (MEFs) deficient for p53 can be transformed with either c-myc or with rasV12 alone. Interestingly, transformation by c-myc is efficiently suppressed by co-expression of Stat3alphaC, but Stat3alphaC does not interfere with transformation by the rasV12-oncogene. In contrast, transplantation of bone marrow cells expressing Stat3alphaC induces the formation of a highly aggressive T cell leukemia in mice. The leukemic cells invaded multiple organs including lung, heart, salivary glands, liver and kidney. Interestingly, transplanted mice developed a similar leukemia when the bone marrow cells were transduced with Stat3beta, which is also constitutively active when expressed at significant levels. Our experiments demonstrate that Stat3 has both - tumor suppressing and tumor promoting properties.