Cell-cycle-dependent expression of human ornithine decarboxylase

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Ornithine decarboxylase (ODC) is a key enzyme in polyamine synthesis, essential for cell growth and proliferation.
• Understanding ODC gene regulation is crucial for comprehending cell cycle control and potential therapeutic interventions.

Purpose of the Study:

• To isolate and characterize a human ODC gene probe.
• To analyze ODC mRNA expression patterns in human lymphocytes and fibroblasts during mitogenic stimulation.
• To investigate the role of growth factors in regulating ODC expression.

Main Methods:

• Isolation and sequencing of a human ODC cDNA expression library from Jurkat T-cells.
• Northern blot analysis to quantify ODC mRNA levels in stimulated and unstimulated cells.
• Southern blot analysis to assess ODC gene copy number.
• Treatment of fibroblasts with growth factors like epidermal growth factor, insulin, and dexamethasone.

Main Results:

• A human ODC cDNA probe was successfully generated, showing 86% homology to mouse ODC cDNA.
• ODC mRNA was undetectable in quiescent lymphocytes and fibroblasts but significantly upregulated upon mitogenic stimulation.
• In T-lymphocytes, ODC mRNA peaked in mid-G1 phase and declined as cells entered S phase.
• Serum stimulation of fibroblasts led to sustained ODC mRNA elevation throughout the cell cycle.
• Epidermal growth factor, but not insulin or dexamethasone, stimulated ODC expression in quiescent fibroblasts.
• Southern blots indicated a single copy of the ODC gene in human cells.

Conclusions:

• Human ODC gene expression is dynamically regulated during the cell cycle, responding to mitogenic signals.
• Specific growth factors play distinct roles in modulating ODC expression in different cell types.
• The findings provide insights into the molecular mechanisms controlling ODC activity in cell proliferation.