Participates in the regulation of cellular Ca(2+) homeostasis, at least partly, by modulating the filling state of the endoplasmic reticulum Ca(2+) store (By similarity). Negatively regulates the ER stress response and positively regulates the stability of V-ATPase subunits ATP6V1A and ATP1B1 by preventing their degradation through an unknown proteasome-independent mechanism (By similarity). Interacts with ATP6V1A. Co-localizes with ATP6V1A in the secretory granules in neuroblastoma cell lines. Highly expressed in the developing lens.