Regulation of Nur77 gene expression by prostanoids in cementoblastic cells

Abstract

Objective The inflammatory cytokine interleukin-1 (IL-1) decreases mineralization by immortalized mouse-derived cementoblastic cells (OC-CM cells), while various prostanoids, including fluprostenol (flup) increase it. Subtraction hybridization conducted on flup- minus IL-1-treated OC-CM cells revealed that one of the primary response genes preferentially induced by flup is the transcription factor Nur77. The objective of this study was to examine the signal transduction cascades regulating prostanoid induction of Nur77 gene expression in OC-CM cells. Methods Confluent OC-CM cells were treated with prostaglandin E2 (PGE2), prostaglandin F2α (PGF2α), specific activators of the various EP prostanoid receptors and of the FP prostanoid receptor, and direct activators/inhibitors of the cyclic AMP-protein kinase A (PKA), protein kinase C (PKC) and intracellular calcium pathways. Nur77 gene expression was examined by mRNA extraction and northern blot analysis. Results PGE2 and PGF2α treatment of OC-CM cells significantly increased Nur77 mRNA expression in a time- and dose-dependent fashion. Both the EP1 prostanoid receptor-specific activator 16, 16 dimethyl PGE2 and the FP prostanoid receptor-specific activator flup significantly increased Nur77 gene expression by OC-CM cells as compared to vehicle-treated controls. Increase in Nur77 gene expression was also observed when direct activators of the PKA, PKC and intracellular calcium pathways were used to treat OC-CM cells. Direct inhibition of the PKA, PKC and intracellular calcium pathways abrogated Nur77 gene expression induced by OC-CM cell treatment with PGE2 and PGF2α. Conclusion Nur77 is a primary gene expressed by OC-CM cells and its induction appears to be mediated by the PKA, PKC and intracellular calcium pathways. Nur77 may affect expression of downstream target genes in OC-CM cells and partially regulate cementoblast cell function.

Prostanoid EP1 receptors mediate up‐regulation of the orphan nuclear receptor Nurr1 by cAMP‐independent activation of protein kinase A, CREB and NF‐κB

“…For example, PGE 2 has been shown to up‐regulate the expression of both Nurr1 and Nur77 in synoviocytes (McEvoy et al ., 2002) and in chondrocytes (Mix et al ., 2007). In cementoblastic cells, PGE 2 was found to up‐regulate the expression of Nur77 through specific activation of the EP 1 receptor (Moldovan et al ., 2009). It is also possible that the effect of the induced expression of Nurr1 in brain cells is different from the constitutive expression of Nurr1 that is required for the maintenance of dopaminergic neurons.…”