Stanniocalcin 2 is a negative modulator of store-operated calcium entry

The regulation of cellular Ca ²⁺ homeostasis is essential for innumerable physiological and pathological processes. Stanniocalcin 1, a secreted glycoprotein hormone originally described in fish, is a well-established endocrine regulator of gill Ca ²⁺ uptake during hypercalcemia. While there are two mammalian Stanniocalcin homologs (STC1 and STC2), their precise molecular functions remain unknown. Notably, STC2 is a prosurvival component of the unfolded protein response. Here, we demonstrate a cell-intrinsic role for STC2 in the regulation of store-operated Ca ²⁺ entry (SOCE). Fibroblasts cultured from Stc2 knockout mice accumulate higher levels of cytosolic Ca ²⁺ following endoplasmic reticulum (ER) Ca ²⁺ store depletion, specifically due to an increase in extracellular Ca ²⁺ influx through store-operated Ca ²⁺ channels (SOC). The knockdown of STC2 expression in a hippocampal cell line also potentiates SOCE, and the overexpression of STC2 attenuates SOCE. Moreover, STC2 interacts with the ER Ca ²⁺ sensor STIM1, which activates SOCs following ER store depletion. These results define a novel molecular function for STC2 as a negative modulator of SOCE and provide the first direct evidence for the regulation of Ca ²⁺ homeostasis by mammalian STC2. Furthermore, our findings implicate the modulation of SOCE through STC2 expression as one of the prosurvival measures of the unfolded protein response.