Adherence-dependent increase in human monocyte PDGF(B) mRNA is associated with increases in c-fos, c-jun, and EGR2 mRNA.

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.

The Human Leukemia Oncogene bcr-abl Abrogates the Anchorage Requirement but Not the Growth Factor Requirement for Proliferation

“…In human monocytes, adherence alone is sufficient to activate the immediateearly response indicated by the induction of c-fos and c-jun expression (52). Interestingly, the activation of c-jun but not c-fos is blocked by cytochalasin D, indicating that cytoskeleton rearrangement is important for the induction of c-jun but not c-fos.…”

Dietary ω-3, ω-6, and ω-9 Unsaturated Fatty Acids and Growth Factor and Cytokine Gene Expression in Unstimulated and Stimulated Monocytes

“…7,11,19,20,28 For monocyte activation and differentiation, we decided to use an established model ex vivo, ie, their adherence to polystyrene. 14,15,32,33 Activating monocytes ex vivo by adherence requires the presence of serum factors. 34 Therefore, we left the monocytes to adhere for 4 or 20 hours in the presence of 5% serum from the respective donor at the respective time point.…”

Signal transduction from the extracellular matrix.

“…High steady-state levels of transcripts for IL-lb, for example, appear in <30 min accounting for ~0.1% of the total mRNA of the cell (123). While many of these immediate-early (IE) response genes encode cytokines, other genes encode transcription-associated proteins, such as c-fos (56), c-jun (118), IrB (58), and MAD-6/A20 (123). Adhesion does not result in a global activation of gene expression in monocytes.…”

“…Although the nuclear translocation of NF-kB is associated with adhesion to plastic (48), adherence to ECM ligands that provide specificity of gene induction is likely to induce the nuclear association of additional positive and/or negative transcription factors, not seen through direct integrin engagement or adhesion to plastic. For example, engagement of VLA-5 on lymphocytes activates the AP-1 transcription complex of fos/jun proteins (140), as does adhesion to plastic (56,118). Thus, at least two distinct enhancer elements, NF-/cB and AP-1, are likely to be activated by adhesion to ECM.…”