Identification of Poly(ADP-Ribose) Polymerase-1 as a Cell Cycle Regulator through Modulating Sp1 Mediated Transcription in Human Hepatoma Cells

Liu Yang,Cheng Wang,Fengxiao Zhang,Dan Huang,Xi Luo,Lu Gao,Xiangrao Li,Xiang Kang,Kun Huang,Qiangsong Tong,Kai Huang,Yanqing Zhang,Meng Du,Chun Zhang,Shaida A Andrabi

doi:10.1371/journal.pone.0082872

Abstract

The transcription factor Sp1 is implicated in the activation of G0/G1 phase genes. Modulation of Sp1 transcription activities may affect G1-S checkpoint, resulting in changes in cell proliferation. In this study, our results demonstrated that activated poly(ADP-ribose) polymerase 1 (PARP-1) promoted cell proliferation by inhibiting Sp1 signaling pathway. Cell proliferation and cell cycle assays demonstrated that PARP inhibitors or PARP-1 siRNA treatment significantly inhibited proliferation of hepatoma cells and induced G0/G1 cell cycle arrest in hepatoma cells, while overexpression of PARP-1 or PARP-1 activator treatment promoted cell cycle progression. Simultaneously, inhibition of PARP-1 enhanced the expression of Sp1-mediated checkpoint proteins, such as p21 and p27. In this study, we also showed that Sp1 was poly(ADP-ribosyl)ated by PARP-1 in hepatoma cells. Poly(ADP-ribosyl)ation suppressed Sp1 mediated transcription through preventing Sp1 binding to the Sp1 response element present in the promoters of target genes. Taken together, these data indicated that PARP-1 inhibition attenuated the poly(ADP-ribosyl)ation of Sp1 and significantly increased the expression of Sp1 target genes, resulting in G0/G1 cell cycle arrest and the decreased proliferative ability of the hepatoma cells.

Highlights

Specificity protein 1 (Sp1) was the first transcription factor identified and cloned in mammalian [1]
We concluded that poly(ADP-ribose) polymerase 1 (PARP-1) played a crucial role in the cell proliferation of hepatoma cells
H2O2 treatment promoted cell proliferation (Figure 1C). These results indicated that PARP-1 catalytic activity was involved in proliferation regulation

Summary

Introduction

Specificity protein 1 (Sp1) was the first transcription factor identified and cloned in mammalian [1]. It belongs to the Sp/ XKLF (Specificity protein/Kruppel-like factor) family, which has been implicated in a host of essential biological processes. The Sp1 protein comprises several domains, including N-terminal inhibitory domain, serine/threonine-rich domains, glutamine-rich domains, zinc finger DNA binding domain, and the C-terminal DNA binding domain. It has been proposed that Sp1 is essential for the transcription of various genes, such as INK4 (including p15, p16, p18 and p19) and Cip/Kip (such as p21 and p27) family genes, which induce cell cycle arrest at G0/G1 phase [5,6,7,8,9,10]. Sp1 plays a critical role in diverse processes, including cell cycle, cell proliferation and apoptosis [11,12,13,14,15,16,17]

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Results

Conclusion