ABSTRACT
We present the first evidence for a fast activation of the nuclear protein poly(ADP-ribose) polymerase (PARP) by signals evoked in the cell membrane, constituting a novel mode of signaling to the cell nucleus. PARP, an abundant, highly conserved, chromatin-bound protein found only in eukaryotes, exclusively catalyzes polyADP-ribosylation of DNA-binding proteins, thereby modulating their activity. Activation of PARP, reportedly induced by formation of DNA breaks, is involved in DNA transcription, replication, and repair. Our findings demonstrate an alternative mechanism: a fast activation of PARP, evoked by inositol 1,4,5,-trisphosphate-Ca(2+) mobilization, that does not involve DNA breaks. These findings identify PARP as a novel downstream target of phospholipase C, and unveil a novel fast signal-induced modification of DNA-binding proteins by polyADP-ribosylation.
Subject(s)
Poly(ADP-ribose) Polymerases/metabolism , Signal Transduction/physiology , Type C Phospholipases/metabolism , Animals , Calcium/metabolism , Calcium Signaling/physiology , Cell Membrane/enzymology , Cell Nucleus/enzymology , Cells, Cultured , Cerebral Cortex/cytology , Cerebral Cortex/enzymology , DNA Damage/physiology , DNA Topoisomerases, Type I/metabolism , Fetus/cytology , Inositol 1,4,5-Trisphosphate/metabolism , Neurons/cytology , Neurons/enzymology , Nuclear Proteins/metabolism , RatsABSTRACT
GTP-binding protein(s) recognized by antibodies against the alpha-subunits of Gi- and Go-proteins were detected in crude nuclei isolated from rat brain stem and cortex. Immunohistochemical staining indicated that in the cortex these proteins are perinuclear, or are embedded in the nuclear membrane. Evidence is presented for an endogenous ADP-ribosylation of these proteins, which competes with their PTX-catalyzed ADP-ribosylation. The endogenous reaction has the characteristics of nonenzymatic ADP-ribosylation of cysteine residues, known to involve NAD-glycohydrolase activity. In vitro experiments showed that the alpha-subunit of Go-proteins in the cell membrane also acts as a substrate of this endogenous ADP-ribosylation. The in situ effect of membrane depolarization on the nuclear GTP-binding proteins may be attributable to their depolarization-induced endogenous ADP-ribosylation, suggesting a novel signaling mechanism in neuronal cells in the central nervous system.
