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Adherence-dependent increase in human monocyte PDGF(B) mRNA is associated with increases in c-fos, c-jun, and EGR2
R J Shaw1, D E Doherty, A G Ritter
1Department of Medicine, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
Abstract:
Adherence is an important initial step in the transition of a circulating monocyte to a tissue macrophage. This differentiation is accompanied by an augmented capacity to generate growth factors. We hypothesized that adherence itself might be an important trigger for a sequence of gene activation culminating in cells with increased mRNA encoding profibrotic growth factors such as platelet-derived growth factor B subunit (PDGF[B]) and transforming growth factor-beta (TGF-beta). After in vitro adherence, human monocytes had a biphasic increase in PDGF(B) mRNA with peaks at 6 h and 13 d. No increase in TGF-beta mRNA was observed. The 6-h increase in PDGF(B) mRNA was adherence dependent, and in addition, was abrogated when the cytoskeletal integrity was compromised by cytochalasin D. The 6-h increase in PDGF(B) mRNA was unaltered by adherence in the presence of the monocyte stimulus lipopolysaccharide. Adherence to either fibronectin or collagen-coated plastic had little consistent effect on PDGF(B) mRNA accumulation. The increased PDGF(B) mRNA observed in adherent monocytes was accompanied by increases in mRNAs of the early growth response genes c-fos (maximal at 20 min), c-jun, and EGR2 (maximal at 6-24 h). The increase in c-jun and EGR2, but not c-fos, mRNA was also abrogated by cytochalasin D. These observations suggest that adherence results in increases of c-fos, c-jun, EGR2, and PDGF(B) mRNA. In addition, the increases in c-jun, EGR2, and PDGF(B) may depend on cytoskeletal rearrangement. Modulation of these events at the time of adherence offers a mechanism by which differential priming of the cells may be accomplished.
Insights
Monocyte adherence triggers gene activation, increasing platelet-derived growth factor B subunit (PDGF(B)) mRNA. This process involves cytoskeletal changes and early growth response genes, influencing cell priming.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- Monocyte to macrophage differentiation is crucial for tissue repair and immune response.
- This transition involves changes in gene expression and growth factor production.
- Adherence to surfaces is a key initial step in monocyte differentiation.
Purpose of the Study:
- To investigate if monocyte adherence triggers gene activation for profibrotic growth factors.
- To determine the role of cytoskeletal integrity in adherence-induced gene expression.
- To explore the relationship between adherence, early growth response genes, and PDGF(B) mRNA levels.
Main Methods:
- In vitro adherence of human monocytes to coated plastic surfaces.
- Quantification of mRNA levels for PDGF(B), TGF-beta, c-fos, c-jun, and EGR2 using techniques like RT-PCR.
- Pharmacological disruption of cytoskeletal integrity using cytochalasin D.
Main Results:
- Monocyte adherence induced a biphasic increase in PDGF(B) mRNA, with peaks at 6 hours and 13 days.
- The 6-hour PDGF(B) mRNA increase was adherence-dependent and abrogated by cytochalasin D.
- Adherence led to increased mRNA for c-fos, c-jun, and EGR2, with c-jun and EGR2 increases also dependent on cytoskeletal integrity.
Conclusions:
- Monocyte adherence is a significant trigger for the upregulation of specific genes, including PDGF(B).
- Cytoskeletal rearrangement plays a critical role in the adherence-induced expression of c-jun, EGR2, and PDGF(B) mRNA.
- These findings suggest a mechanism for differential cell priming during monocyte differentiation.