Human PARP2 Knockdown Cell Line-HeLa

Case Study Initiation, amplitude, duration and termination of transforming growth factor β (TGFβ) signaling via Smad proteins is regulated by post-translational modifications, including phosphorylation, ubiquitination and acetylation. Previously, ADP-ribosylation of Smads by poly(ADP-ribose) polymerase 1 (PARP-1) has been reported to affect Smad-mediated transcription negatively. PARP-1 is known to interact with PARP-2 in the nucleus functionally, and the enzyme poly(ADP-ribose) glycosyl hydrolase (PARG) can remove poly(ADP-ribose) chains from target proteins. Here, researchers found that PARP-2 overexpression repressed the Smad3/4 promoter, and PARP-2 siRNA knockdown resulted in increased expression of TGFβ gene targets fibronectin and Smad7, with PARP-2 playing an inhibitory role in this pathway.

First, the study demonstrated that specific silencing of PARP-2 did not affect PARP-1 expression, and silencing of PARP-1 did not affect PARP-2 expression (Fig. 1e, f). Under these conditions, the researchers measured the responsiveness of classical gene targets of TGFβ/Smad signaling, such as fibronectin and Smad7 (Fig. 1g, h). When measured 9 hours after TGFβ stimulation, PARP-1 knockdown enhanced the response of both genes, while PARP-2 knockdown led to an even more robust enhancement of the gene response. Simultaneous knockdown of PARP-1 and PARP-2 had almost the same effect on gene expression in response to TGFβ as the knockdown of PARP-2 alone (Fig. 1g, h). Thus, the study suggests that PARP-2, like PARP-1, can play a negative regulatory role in TGFβ signaling.

Figure 1. Regulation of gene expression by PARP-1 and PARP-2 during TGFβ signaling. (Dahl M, et al., 2014)