Abnormal expression of interleukin-3 and leukaemia

Area of Science:

• Molecular Biology
• Cancer Research
• Cell Biology

Background:

• Autonomous growth factor production is a key step in tumorigenesis.
• Leukemias can exhibit autocrine stimulation via secreted growth factors.
• WEHI-3B myelomonocytic leukemia constitutively produces interleukin-3 (IL-3).

Purpose of the Study:

• Investigate genetic alterations in the IL-3 gene of WEHI-3B cells.
• Determine the role of IL-3 gene rearrangement in leukemogenesis.
• Experimentally induce leukemia by abnormal IL-3 expression.

Main Methods:

• Gene cloning and sequencing of the IL-3 gene in WEHI-3B cells.
• Transfection of IL-3 responsive cell lines (FDC-P1, 32D cl-23) and bone marrow cells with an IL-3 expression vector.
• Analysis of cell proliferation, differentiation, and leukemogenicity post-transfection.
• Neutralization of IL-3 activity using antiserum.

Main Results:

• A 5.1 kb intracisternal A-type particle genome was inserted head-to-head with the IL-3 gene in WEHI-3B cells, 215 bases upstream of the TATA box.
• The rearranged IL-3 gene was aberrantly expressed in COS-1 cells, unlike the normal gene.
• Transfection of FDC-P1 and 32D cl-23 cells with the IL-3 gene resulted in autonomous IL-3 production and induced leukemogenicity.
• Transfected bone marrow cells produced IL-3 and could be maintained but did not become leukemogenic, retaining differentiation capacity.

Conclusions:

• Insertion of an endogenous retroviral element into the IL-3 gene is a critical genetic event in WEHI-3B leukemia development.
• Abnormal IL-3 expression via autocrine stimulation can induce leukemogenesis in factor-dependent cell lines.
• Tumorigenicity likely requires additional genetic changes that inhibit cell differentiation, beyond autocrine IL-3 signaling.