Control of XPR1-dependent cellular phosphate efflux by InsP <sub>8</sub> is an exemplar for functionally-exclusive inositol pyrophosphate signaling
Xingyao Li, Chunfang Gu, Sarah Hostachy, Soumyadip Sahu, Christopher Wittwer, Henning J. Jessen, Dorothea Fiedler, Huanchen Wang, Stephen B. Shears
Abstract
Significance Biological roles of inorganic phosphate require careful regulation of its transport across cell membranes, but mechanisms are poorly understood. We demonstrate that a major cellular phosphate export protein, XPR1, is regulated by the most “energetic” of cell signaling molecules—1,5-bisdiphosphoinositol 1,2,3,4-tetrakisphosphate (InsP 8 ). We derive this conclusion by showing reduced XPR1-mediated phosphate efflux when InsP 8 synthesis was attenuated by genetic or pharmacological techniques; phosphate efflux was rescued by using liposomes to deliver into cells metabolically resistant InsP 8 analogues. Genetic elimination of InsP 8 from an osteosarcoma cell line perturbed phosphate homeostasis and accelerated differentiation into a biomineralization phenotype. We propose that mutations in gene products that regulate InsP 8 synthesis might compromise XPR1 function, with pathological consequences for bone maintenance and ectopic calcification.