Interactions between extracellular signal-regulated kinase 1/2 and P38 Map kinase pathways in the control of RUNX2 phosphorylation and transcriptional activity

Abstract

RUNX2, a key transcription factor for osteoblast differentiation, is regulated by ERK1/2 and p38 MAP kinase-mediated phosphorylation. However, the specific contribution of each kinase to RUNX2-dependent transcription is not known. Here we investigate ERK and p38 regulation of RUNX2 using a unique P-RUNX2-specific antibody. Both MAP kinases stimulated RUNX2 Ser319 phosphorylation and transcriptional activity. However, a clear preference for ERK1 versus p38α/β was seen when the ability of these MAPKs to phosphorylate and activate RUNX2 was compared. Similarly, ERK1 preferentially bound to a consensus MAPK binding site on RUNX2 that was essential for the activity of either kinase. To assess the relative contribution of ERK1/2 and p38 to osteoblast gene expression, MC3T3-E1 preosteoblast cells were grown in control or ascorbic acid (AA)-containing medium ± BMP2/7. AA-induced gene expression, which requires collagen matrix synthesis, was associated with parallel increases in P-ERK and RUNX2-S319-P in the absence of any changes in P-p38. This response was blocked by ERK, but not p38, inhibition. Significantly, in the presence of AA, BMP2/7 synergistically stimulated RUNX2 S319 phosphorylation and transcriptional activity without affecting total RUNX2 and this response was totally dependent on ERK/MAPK activity. In contrast, although p38 inhibition partially blocked BMP-dependent transcription, it did not affect RUNX2 S319 phosphorylation, suggesting the involvement of other phosphorylation sites and/or transcription factors in this response. Based on this work, we conclude that extracellular matrix and BMP regulation of RUNX2 phosphorylation and transcriptional activity in osteoblasts is predominantly mediated by ERK rather than p38 MAPKs.

Intracellular Modulation of Signaling Pathways by Annexin A6 Regulates Terminal Differentiation of Chondrocytes

“…In addition, nuclear translocation requires the association of ERK with partner proteins via the common docking motif (31). Activated (phosphorylated) cytoplasmic ERK and p38 have been shown to phosphorylate linker regions of Smads, the main downstream transcription factors of transforming growth factor (TGF) ␤ and bone morphogenetic protein signaling, and runx2, thereby regulating the transcription activities of these Smads and runx2 (32,33). TGF␤-and bone morphogenetic protein-mediated Smad signaling and runx2 transcription activity play major roles in chondrocyte terminal differentiation (5,30).…”

Potential mechanisms and applications of statins on osteogenesis: Current modalities, conflicts and future directions

“…Furthermore, MAPK may regulate lovastatin induced osteogenesis because of the partial inhibition of BMP-2 gene expression by dominant negative ERK2 [67]. BMP-2…”

O-GlcNAc Modification of the runt-Related Transcription Factor 2 (Runx2) Links Osteogenesis and Nutrient Metabolism in Bone Marrow Mesenchymal Stem Cells

“…BMPs are known to stimulate osteoblast differentiation by increasing Runx2 phosphorylation and transactivation (17,65). To test whether acute BMP2/7-stimulation alone affected the relative abundance of Runx2 O-GlcNAc modification, BMMSCs were serum-starved for 18 h and cultured under osteogenic conditions for 24 or 48 h in the absence or presence of BMP2/7.…”