Connexin43 regulates osteoprotegerin expression via ERK1/2 -dependent recruitment of Sp1

Abstract

In bone, connexin43 expression in cells of the osteoblast lineage plays an important role in restraining osteoclastogenesis and bone resorption. While there is a consensus around the notion that the anti-osteoclastogenic factor, osteoprotegerin, is a driver of this effect, how connexin43 regulates osteoprotegerin gene expression is unclear. Here, we showed that loss of connexin43 decreased osteoprotegerin gene expression and reduced ERK1/2 activation. Conversely, overexpression of connexin43 increased osteoprotegerin expression and enhanced ERK1/2 activation. This increase in phospho-ERK1/2 is required for connexin43 to induce activity from the osteoprotegerin proximal promoter. Connexin43 increased promoter activity via a specific 200 base pair region of the osteoprotegerin promoter located at −1486 to −1286 with respect to the transcriptional start site, a region which includes four Sp1 binding elements. Further, activation of this promoter region required an intact functional connexin43, as hypomorphic or dominant negative connexin43 mutant constructs, including one with increased hemichannel activity, were unable to stimulate osteoprotegerin expression as strongly as wild type connexin43. Using chromatin immunoprecipitations, we show that connexin43 expression enhanced the recruitment of Sp1, but not Runx2, to the osteoprotegerin proximal promoter. In total, these data show that connexin43-dependent gap junctional communication among osteoblast cells permits efficient ERK1/2 activation. ERK1/2 signaling promoted the recruitment of the potent transcriptional activator, Sp1, to the osteoprotegerin proximal promoter, resulting in robust transcription of antiosteoclastogenic factor, osteoprotegerin.

Cx43 phosphorylation–mediated effects on ERK and Akt protect against ischemia reperfusion injury and alter the stability of the stress-inducible protein NDRG1

“…3C). Interestingly, it was recently reported that Cx43 expression in osteoblasts could alter ERK activity (38); in this case, Cx43 knockdown diminished ERK phosphorylation, whereas overexpression increased ERK phosphorylation. This is certainly distinct from our data, as we saw an ERK effect in animals expressing the lowest total levels of Cx43 (old Cx43 CK1 mice, Fig.…”

StarD7 deficiency hinders cell motility through p-ERK1/2/Cx43 reduction

“…Numerous evidences reveal that ERK pathways play an important role in promoting cell motility [28,29]. Although, several studies indicate that ERK1/2 signaling pathway regulates Cx43 [37][38][39][40][41]; other reports involves Cx43 in the regulation of ERK1/2 signaling pathway [30][31][32][33]. Our data demonstrate that ERK1/2 phosphorylation was recovered by the addition of either StarD7 isoforms but not by exogenous Cx43, indicating that in this cell model ERK1/2 phosphorylation is upstream of Cx43.…”

“…Numerous evidences reveal that ERK pathways are required to promote cell motility [28,29]. In addition, several reports indicate that Cx43 is involved in regulating ERK1/2 signaling [30][31][32][33][34]. Thus, we explored the expression of p-ERK1/2 in StarD7-silenced cells.…”

Connexin43 in mesenchymal lineage cells regulates body adiposity and energy metabolism in mice

“…Upregulation of Adipoq mRNA in WAT and in differentiating EMSCs supports the idea that increased production of adiponectin or other adipokines, or endocrine factors may in part explain increased glucose utilization and energy consumption by cKO Tw2 mice. We and others have shown that Cx43 modulates the expression of factors relevant to bone homeostasis via transcriptional regulation (42,43), and a similar mechanism might be at play in the adipogenic lineage. It is also possible that adipokines produced by BAT (batokines) may play a role, as Cx43 is abundantly expressed in BAT and is upregulated by high caloric intake.…”