PIGBOS-CLCC1 Interaction Shapes Cellular Calcium Dynamics and Energy Metabolism

Abstract 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 Ca 2+ homeostasis. Manipulation of PIGBOS expression in HEK293T cells revealed that PIGBOS enhances Ca 2+ signaling by promoting ER Ca 2+ release through inositol 1,4,5-trisphosphate (IP 3 ) receptors and subsequent mitochondrial Ca 2+ uptake in response to histamine stimulation. In contrast, siRNA-mediated depletion or genetic ablation of PIGBOS markedly attenuated these responses. PIGBOS selectively facilitated Ca 2+ transfer from the ER to mitochondria without affecting mitochondrial Ca 2+ uptake from non-ER sources and also promoted store-operated Ca 2+ 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 Ca 2+ signaling components, including IP 3 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 Ca 2+ signaling that couples Ca 2+ dynamics to mitochondrial bioenergetics and cellular stress responses. Significance Statement This study identifies PIGBOS, a mitochondrial microprotein, as a key regulator of cellular Ca 2+ signaling through its interaction with the endoplasmic reticulum (ER) chloride channel CLCC1. By coordinating ER–mitochondrial Ca 2+ transfer and modulating the expression of key Ca 2+ signaling–associated proteins, PIGBOS integrates cellular Ca 2+ dynamics with mitochondrial energy metabolism and stress responses. Given that perturbations in Ca 2+ homeostasis profoundly influence cell survival and energy production, these findings reveal a new paradigm of inter-organelle communication. This work has broad implications for understanding the molecular basis of disorders such as neurodegeneration and cancer, where Ca 2+ signaling and homeostasis are disrupted.