PIGBOS-CLCC1 interaction shapes cellular calcium dynamics and energy metabolism

PIGBOS is a recently identified 54-amino acid microprotein localized to the mitochondrial outer membrane and implicated in the endoplasmic reticulum (ER) stress response. Here, we identify a previously unrecognized role for PIGBOS in cellular Ca²⁺ homeostasis. Manipulation of PIGBOS expression in HEK293T cells revealed that PIGBOS enhances Ca²⁺ signaling by promoting ER Ca²⁺ release through inositol 1,4,5-trisphosphate (IP₃) receptors and subsequent mitochondrial Ca²⁺ uptake in response to histamine stimulation. In contrast, siRNA-mediated depletion or genetic ablation of PIGBOS markedly attenuated these responses. PIGBOS influenced Ca²⁺ transfer from the ER to mitochondria without affecting direct mitochondrial Ca²⁺ uptake and also promoted store-operated Ca²⁺ entry. Functional analyses demonstrated that the interaction of PIGBOS with the ER-resident chloride channel CLCC1 via its C-terminal region is required for this activity. Network analysis predicted a direct association between PIGBOS and CLCC1, as well as indirect connections with core Ca²⁺ signaling components, including IP₃ receptors, STIM1, Orai1, and SERCA, whose expression was altered upon modulation of PIGBOS abundance. Loss of PIGBOS impaired mitochondrial respiration, reduced ATP production, and increased reactive oxygen species. Together, these findings establish PIGBOS as a key regulator of ER-mitochondrial Ca²⁺ signaling that couples Ca²⁺ dynamics to mitochondrial bioenergetics and cellular stress responses.