Endoplasmic reticulum D-myo-inositol 1,4,5-trisphosphate-sensitive stores regulate nuclear factor-kappa B binding activity in a calcium-dependent manner
The transcription factor nuclear factor-kappaB (NF-kappaB) plays critical r
oles in neuronal survival and plasticity and in activation of immune respon
ses. The activation of NF-kappaB has been closely associated with changes i
n intracellular calcium levels, but the relationship be tween the two remai
ns unclear. Here we report that inhibition of endoplasmic reticulum (ER) D-
myo-inositol 1,4,5-trisphosphate (IP3)-gated calcium release caused decreas
ed basal NF-kappaB DNA-binding activity in cultured rat cortical neurons. A
ctivation of NF-kappaB in response to tumor necrosis factor-alpha and gluta
mate was completely abolished when IP3 receptors were blocked, and NF-kappa
B activation in response to depletion of ER calcium by thapsigargin treatme
nt was also decreased by IP3 receptor blockade, We further investigated the
relationship between IP3 receptor activation and NF-kappaB activity using
a cell-free system. Microsomes enriched in the ER were isolated from adult
rat cerebral cortex, resuspended, and treated with agents that induce or in
hibit ER calcium release, They were then recentrifuged, and the supernatant
was added to cytoplasmic extract isolated from the same source tissue. We
found that microsomes released an NF-kappaB stimulating signal in response
to activation of IP3 receptors or inhibition of the ER Ca2+-ATPase, but not
in response to ryanodine. Studies of intact cells and cell-free preparatio
ns indicated that the signal released from the ER was not calcium and was h
eat- and trypsin sensitive. Our data suggest that activation of IP3 recepto
rs is required for a major component of both constitutive and inducible NF-
kappaB binding activity in neurons and that decreasing ER intraluminal calc
ium levels triggers release of a diffusible NF-kappaB-activating signal fro
m the ER.