Erk1/2 signaling is required for Tgf-β2-induced suture closure

Abstract

Transforming growth factors β (Tgf-βs) act by means of Smad signaling pathways and may also interact with the mitogen-activated protein kinase pathway. The hypothesis was tested that Erk1/2 signaling is required for Tgf-β2-induced suture closure, by culturing embryonic mouse calvariae in the presence of Tgf-β2 with or without Erk1/2 inhibitor PD88059 (PD). Suture widths were measured daily, and microdissected sutures and bones were homogenized and protein analyzed by Western blots. Tgf-β2 induced narrowing of the sutures after 72 hr, an effect inhibited by treatment with PD. Erk1/2 and Egf but not Smad2/3 protein expression was up-regulated by Tgf-β2 calvarial tissues at 72 hr. PD inhibited endogenous and Tgf-β2-stimulated Erk1/2 protein as well as Tgf-β2-stimulated Egf, but increased Smad2/3 protein expression. In tissues harvested 0, 15, and 30 min after exposure to Tgf-β2, Erk1/2 phosphorylation was up-regulated after 15 min, an effect abrogated by the simultaneous addition of PD. In summary, Tgf-β2 stimulated Erk1/2 phosphorylation and induced Egf and Erk1/2 expression, associated with suture closure after 72 hr. Blocking Erk1/2 activity with PD inhibited these effects but increased Smad2/3 expression. We postulate that Tgf-β2 regulates suture closure directly by means of phosphorylation of Erk1/2 and indirectly by up-regulating Erk1/2, a substrate for Fgf receptor signaling required for Fgf induction of premature suture obliteration. © 2005 Wiley-Liss, Inc.