In smooth muscle, FK506-binding protein modulates IP3 receptor-evoked Ca2+ release by mTOR and calcineurin

Abstract

Ca2+ release from the sarcoplasmic reticulum (SR) by the IP3 receptors (IP3Rs) crucially regulates diverse cell signalling processes from reproduction to apoptosis. Release from the IP3R may be modulated by endogenous proteins associated with the receptor, such as the 12 kDa FK506-binding protein (FKBP12), either directly or indirectly by inhibition of the phosphatase calcineurin. Here, we report that, in addition to calcineurin, FKPBs modulate release through the mammalian target of rapamycin (mTOR), a kinase that potentiates Ca2+ release from the IP3R in smooth muscle. The presence of FKBP12 was confirmed in colonic myocytes and co-immunoprecipitated with the IP3R. In aortic smooth muscle, however, although present, FKBP12 did not co-immunoprecipitate with IP3R. In voltage-clamped single colonic myocytes rapamycin, which together with FKBP12 inhibits mTOR (but not calcineurin), decreased the rise in cytosolic Ca2+ concentration ([Ca2+]c) evoked by IP3R activation (by photolysis of caged IP3), without decreasing the SR luminal Ca2+ concentration ([Ca2+]l) as did the mTOR inhibitors RAD001 and LY294002. However, FK506, which with FKBP12 inhibits calcineurin (but not mTOR), potentiated the IP3-evoked [Ca2+]c increase. This potentiation was due to the inhibition of calcineurin; it was mimicked by the phosphatase inhibitors cypermethrin and okadaic acid. The latter two inhibitors also prevented the FK506-evoked increase as did a calcineurin inhibitory peptide (CiP). In aortic smooth muscle, where FKBP12 was not associated with IP3R, the IP3-mediated Ca2+ release was unaffected by FK506 or rapamycin. Together, these results suggest that FKBP12 has little direct effect on IP3-mediated Ca2+ release, even though it is associated with IP3R in colonic myocytes. However, FKBP12 might indirectly modulate Ca2+ release through two effector proteins: (1) mTOR, which potentiates and (2) calcineurin, which inhibits Ca2+ release from IP3R in smooth muscle

Molecular Consequences of the ACVR1R206H Mutation of Fibrodysplasia Ossificans Progressiva

“…It interacts with multiple intracellular calcium release channels including the tetrameric skeletal muscle ryanodine receptor, and the immunosuppressants FK506 and rapamycin, as well as type I receptors of the TGF-␤ superfamily (56). A reduction in the ACVR1-FKBP1A interaction by the R206H mutation may lead to a decrease in the steady-state ACVR1 protein level and to a different subcellular distribution.…”

Inositol Trisphosphate Receptor Ca2+Release Channels

“…Physiologically, the rapamycin-FKBP12 complex inhibits mTOR (mammalian target of rapamycin), a protein kinase that regulates growth and cell cycle progression (247). Rapamycin was shown to inhibit Ca 2ϩ release from cerebral microsomes (100) and in intact cells (268). It has been proposed that the InsP 3 R is a target for mTOR and that rapamycin-FKBP12 inhibition of mTOR reduces channel phosphorylation to inhibit Ca 2ϩ release (268).…”

“…Rapamycin was shown to inhibit Ca 2ϩ release from cerebral microsomes (100) and in intact cells (268). It has been proposed that the InsP 3 R is a target for mTOR and that rapamycin-FKBP12 inhibition of mTOR reduces channel phosphorylation to inhibit Ca 2ϩ release (268). In summary, whereas it appears that FKBP12 may not directly modulate the InsP 3 R, it may influence channel activity by interacting with effector proteins involved in regulating the phosphorylation status of the InsP 3 R. However, the inconsistency among the data and the reliance on pharmacological manipulations suggest that at present such models must be regarded as highly speculative.…”

Agonist‐evoked Ca2+ wave progression requires Ca2+ and IP3

“…Membrane currents were measured using conventional tight seal whole-cell recording methods previously described Kamishima and McCarron, 1998;MacMillan et al, 2005b). The normal extracellular solution contained (mM): Na glutamate (80), NaCl (40), tetraethylammonium chloride (TEA) (20), MgCl 2 (1.1), CaCl 2 (3), Hepes (10) and glucose (30) (pH 7.4 with NaOH).…”