Hypothetical model. Model showing DPP-mediated intracellular calcium store flux can trigger the activation of CaMKII, resulting in the activation of Smad1/5/8 signaling cascade. ER, endoplasmic reticulum; SERCA, sarco/endoplasmic reticulum Ca2+-ATPase; IP3R, inositol 1,4,5-trisphosphate receptor.