Etoposide-induced protein 2.4 functions as a regulator of the calcium ATPase and protects pancreatic -cell survival

Calcium homeostasis is essential for maintaining the viability and function of pancreatic cells and plays a key role in preventing the development of diabetes. Decreased levels of ATPase sarcoplasmic/endoplasmic reticulum Ca2+-transporting 2 (ATP2a2), the main calcium pump in cells, are often found in individuals with diabetes and in diabetic animal models. However, the regulators of ATP2a2 and the molecular mechanisms responsible for controlling ATP2a2 activity remain unclear. Etoposide-induced protein 2.4 (Ei24) is also down-regulated in cells of diabetic individuals, whereas the effect of decreased Ei24 level on -cell function is not clarified. Here, using Cre-LoxP and CRISPR/Cas9-based genomic knockout (KO) approaches to generate pancreatic cell-specific Ei24 KO mice and pancreatic -cell lines, we found that Ei24 regulates ATP2a2 activity. Specifically, we observed that Ei24 binds to ATP2a2 through Ei24 residues 293-299, which we named here the ATP2a2-interacting region (AIR). Loss of Ei24 inactivated ATP2a2, disrupted calcium homeostasis, and deactivated the calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2)-AMP-activated protein kinase (AMPK) pathway. Elevation of calcium concentration in the endoplasmic reticulum or agonist-induced AMPK activation rescued pancreatic -cell survival and improved glucose tolerance of Ei24 KO mice. Our findings indicate that targeting the Ei24-ATP2a2 interaction to increase ATP2a2 activity can protect pancreatic cells and improve glucose homeostasis in diabetic models, suggesting that Ei24 could potentially serve as a target to prevent or manage diabetes.