Poly(ADP-ribose) polymerase-1 and its cleavage products differentially modulate cellular protection through NF-kB-dependent signaling

• PARP-1 mutants (uncleavable and 24 kDa) increase cell viability in in vitro ischemia.
• PARP-1 cleavage products (24 kDa and 89 kDa) have opposite effects on cell viability.
• No augmentation of NF-kB and iNOS activity was seen in protected cells.

Poly(ADP-ribose) polymerase-1 (PARP-1) and its cleavage products regulate cell viability and NF-kB activity when expressed in neurons. PARP-1 cleavage generates a 24 kDa (PARP-124) and an 89 kDa fragment (PARP-189). Compared to WT (PARP-1WT), the expression of an uncleavable PARP-1 (PARP-1UNCL) or of PARP-124 conferred protection from oxygen/glucose deprivation (OGD) or OGD/restoration of oxygen and glucose (ROG) damage in vitro, whereas expression of PARP-189 was cytotoxic. Viability experiments were performed in SH-SY5Y, a human neuroblastoma cell line, as well as in rat primary cortical neurons. Following OGD, the higher viability in the presence of PARP-1UNCL or PARP-124 was not accompanied with decreased formation of poly(ADP-riboses) or higher NAD levels. PARP-1 is a known cofactor for NF-kB, hence we investigated whether PARP-1 cleavage influences the inflammatory response. All PARP-1 constructs mimicked PARP-1WT in regard to induction of NF-kB translocation into the nucleus and its increased activation during ischemic challenge. However, expression of PARP-189 construct induced significantly higher NF-kB activity than PARP-1WT; and the same was true for NF-kB-dependent iNOS promoter binding activity. At a protein level, PARP-1UNCL and PARP-124 decreased iNOS (and lower levels of iNOS transcript) and COX-2, and increased Bcl-xL. The increased levels of NF-kB and iNOS transcriptional activities, seen with cytotoxic PARP-189, were accompanied by higher protein expression of COX-2 and iNOS (and higher levels of INOS transcript) and lower protein expression of Bcl-xL. Taken together, these findings suggest that PARP-1 cleavage products may regulate cellular viability and inflammatory responses in opposing ways during in vitro models of “ischemia”.

Green areas (left and right) indicate events that have been investigated in this study. The formation of the multiprotein complex between PARP-1 and NF-kB (p65+p50) is a known phenomenon in the literature (see Refs. [11], [20] and [57]). The orange area in the middle represents a hypothetical mechanism that might explain the differential expression of downstream effectors of NF-kB and cell viability.Figure optionsDownload high-quality image (199 K)Download as PowerPoint slide