krox‐20/egr‐2 is up‐regulated following non‐specific and homophilic adhesion in rat macrophages

Abstract

SUMMARYMacrophages are known to adhere to a plastic dish via b 2 integrin (CR3) and scavenger receptors. Although their functions such as phagocytosis, endocytosis, and nitric oxide production have been investigated on adherent macrophages in vitro, very little is known about intracellular signals triggered by adhesion to a plastic dish. Recently we reported that the mRNA level of krox-20/egr-2 was significantly increased in rat alveolar macrophages following exposure to fibrous titanium dioxide particles. In the present study we report that up-regulation of krox-20/egr-2 gene expression following adhesion to a plastic dish and homophilic adhesion in rat alveolar macrophages and rat macrophage cell line, NR8383. The mRNA level of krox-20/egr-2 increased with a peak 1 hr after adhesion to a plastic dish in both cell types. Piceatannol inhibited tyrosine-phosphorylation of Syk and decreased both adhesion and krox-20/egr-2 mRNA level. In contrast staurosporine, a serine/threonine kinase inhibitor, increased adherence of macrophages and yet prohibited the adhesion-dependent increase in krox-20/egr-2 gene expression. When NR8383 cells are cultured in suspension, the cells aggregated naturally and produced cell clumps. The mRNA level of krox-20/egr-2 also increased in response to the homophilic intercellular adhesion. The increased mRNA level of krox-20/egr-2 was not caused by inflammatory stimuli, because lipopolysaccharide did not affect the aggregation-dependent up-regulation of krox-20/egr-2 gene. The up-regulation of krox-20/egr-2 gene due to the homophilic cell aggregation was also inhibited either by piceatannol or staurosporine. Those results suggest that krox-20/egr-2 gene expression is triggered by sensing non-specific and homophilic cellular adhesion and the following phosphorylation of signal transducing proteins including Syk and staurosporine-inhibitable kinases.

Dynamic changes in the osteoclast cytoskeleton in response to growth factors and cell attachment are controlled by β3 integrin

“…To find the receptor mediating Pyk2 phosphorylation in response to cell adhesion, we turned to the β2 integrin, which is expressed in pre-OCs (Fig. S1) and is known to be a plastic receptor ( Hirano et al, 2002 ). Thus, β3 +/+ , β3 −/− , and β2 −/− pre-OCs were maintained in suspension or plated on VN or uncoated plastic for 30 min ( Fig.…”

Loading-related Regulation of Transcription Factor EGR2/Krox-20 in Bone Cells Is ERK1/2 Protein-mediated and Prostaglandin, Wnt Signaling Pathway-, and Insulin-like Growth Factor-I Axis-dependent

“…EGR2 is a transcription factor previously shown to be involved in a number of processes in a number of cell types. It plays a role in neuronal myelination ( 49 ) (it is often mutated in Charcot Marie-Tooth syndrome ( 50 ), hindbrain patterning ( 51 – 53 ), and macrophage function ( 54 )) and is activated in wound healing ( 55 ), excitotoxic shock in neuronal tissue ( 56 ), and alveolar macrophage challenge by small particles ( 57 ). Mice lacking both Egr2 alleles display low bone mass, suggesting a significant role in skeletal homeostasis ( 20 , 58 ).…”

Triggering Receptor Expressed on Myeloid Cells 1 (TREM-1)-mediated Bcl-2 Induction Prolongs Macrophage Survival

“…Egr proteins comprise a family of transcriptional regulators (Egr1-4) that modulate gene expression involved in the growth, differentiation, and survival of a variety of cell types (55)(56)(57)(58). Egr1 and Egr2 have been implicated in regulating differentiation of inflammatory cells (57,59). The expression of Egr2 is dependent on ERK and calcineurin signaling; the endogenous repressor Nab2 inhibits Egr2 in neurons and T cells (30, 36, 60 -62).…”