TGF-β autocrine signaling at secretory-stage enamel

Latent TGF-β1 produced and secreted from secretory-stage ameloblasts is activated by MMP20, and the activated TGF-β1 maintains its activity by combining with amelogenin cleavage products processed by the same protease. TGF-β1 moves through the aqueous phase with the water-soluble 13 kDa amelogenin and binds to its receptor on the ameloblast surface, thereby inducing autocrine signaling. Once the ameloblasts differentiate and enter the maturation stage, TGF-β1 is degraded by KLK4, which is produced and secreted by maturation-stage ameloblasts, and loses its activity.