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Abstract
High concentration of extracellular ADP has been reported to induce cell apoptosis, but the molecular mechanisms remain not fully elucidated. In this study, we found by serendipity that ADP treatment of human umbilical vein endothelial cells (HUVEC) and human aortic endothelial cells (HAEC) down-regulated the protein level of nucleolin in a dose- and time-dependent manner. ADP treatment did not decrease the transcript level of nucloelin, suggesting that ADP might induce nucleolin protein degradation. HUVEC and HAEC expressed ADP receptor P2Y13 receptor, but did not express P2Y1 or P2Y12 receptors. However, P2Y1, 12, 13 receptor antagonists MRS2179, PSB0739, MRS2211 did not inhibit ADP-induced down-regulation of nucleolin. Moreover, MRS2211 itself down-regulated nucleolin protein level. In addition, 2-MeSADP, an agonist for P2Y1, 12 and 13 receptors, did not down-regulate nucleolin protein. These results suggested that ADP-induced nucleolin down-regulation was not due to the activation of P2Y1, 12, or 13 receptors. We also found that ADP treatment induced cell cycle arrest in S phase, cell apoptosis and cell proliferation inhibition via nucleolin down-regulation. The over-expression of nucleolin by gene transfer partly reversed ADP-induced cell cycle arrest, cell apoptosis and cell proliferation inhibition. Furthermore, ADP sensitized HUVEC to cisplatin-induced cell death by the down-regulation of Bcl-2 expression. Taken together, we found, for the first time to our knowledge, a novel mechanism by which ADP regulates cell proliferation by induction of cell cycle arrest and cell apoptosis via targeting nucelolin.
Highlights
Nucleolin, an abundant, ubiquitously expressed protein, is composed of three main domains: a N-terminal segment with multiple phosphorylation sites, a central domain with four RNArecognition motifs (RRMs) and a C-terminal arginine–glycine-rich (RGG) domain [1,2]
Adenosine diphosphate (ADP) down-regulates protein level of nucleolin By serendipity, we found that ADP treatment of human umbilical vein endothelial cells (HUVEC)
To test whether ADP down-regulated nucleolin expression via inhibition of nucleolin transcription, HUVEC were treated with various concentrations of ADP for 72 h, and mRNA levels of nucleolin were detected by Quantitative Real Time RT-PCR (qRT-PCR)
Summary
An abundant, ubiquitously expressed protein, is composed of three main domains: a N-terminal segment with multiple phosphorylation sites, a central domain with four RNArecognition motifs (RRMs) and a C-terminal arginine–glycine-rich (RGG) domain [1,2]. Nucleolin is found in various cell compartments, especially in the nucleolus, of which it is a major component and functions as a prominent RNA-binding protein (RBP) to interacts with precursor ribosomal (r)RNA and is essential for rRNA biogenesis and rRNA transport to the cytoplasm [1,3]. Nucleolin was found to function associated with binding DNA to induce chromatin decondensation by the remodelin complex SWI/SNF (switch/sucrose non-fermentable in yeast), facilitates transcription and modulates DNA replication [2,5]. By binding mRNAs, nucleolin has been reported to regulate the expression of Bcl-2 and selenoprotein [16,17]
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