cADP-ribose/ryanodine channel/Ca2+-release signal transduction pathway in mesangial cells

Signaling via release of Ca2+ from intracellular stores is mediated by seve ral systems, including the inositol 1,4,5-trisphosphate (IP3) and cADP-ribo se (cADPR) pathway. We recently discovered a high capacity for cADPR synthe sis in rat glomeruli and cultured mesangial cells (MC). We sought to determ ine whether 1) cADPR synthesis in MC is regulated by cytokines and hormones , 2) ryanodine receptors (RyRs) are expressed in MC, and 3) Ca2+ is release d through RyRs in response to cADPR. We found that ADP-ribosyl cyclase, a C D38-like enzyme that catalyzes cADPR synthesis, is upregulated in MC by tum or necrosis factor-alpha, interleukin-1 beta, and all-trans retinoic acid ( atRA). [H-3]ryanodine binds to microsomal fractions from MC with high affin ity in a Ca2+-dependent manner; binding is enhanced by specific RyR agonist s and blocked by ruthenium red and cADPR. Western blot analysis confirmed t he presence of RyR in MC. Release of Ca-45(2+) from MC microsomes was stimu lated by cADPR; release was blocked by ruthenium red and 8-bromo-cADPR. ADP R (non-cyclic) was without effect. In MC, TNF-alpha and atRA amplified the increment of cytoplasmic Ca2+ elicited by vasopressin. We conclude that MC possess elements of a novel ADP-ribosyl cyclase-->cADPR-->RyR-->Ca2+-releas e signaling pathway subject to regulation by proinflammatory cytokines and steroid superfamily hormones.