Mukudai Yoshiki, Kubota Satoshi, Kawaki Harumi, Kondo Seiji, Eguchi Takanori, Sumiyoshi Kumi, Ohgawara Toshihiro, Shimo Tsuyoshi, Takigawa Masaharu
Biodental Research Center, Okayama University Dental School, Okayama 700-8525, Japan.
Mol Cell Biol. 2008 Oct;28(19):6134-47. doi: 10.1128/MCB.00495-08. Epub 2008 Aug 4.
CCN2/CTGF is a multifunctional factor that plays a crucial role in the growth and differentiation of chondrocytes. The chicken ccn2 gene is regulated not only at the transcriptional level but also by the interaction between a posttranscriptional element in the 3' untranslated region (3'-UTR) and a cofactor. In the present study, we identified a nucleophosmin (NPM) (also called B23) as this cofactor. Binding of NPM to the element was confirmed, and subsequent analysis revealed a significant correlation between the decrease in cytosolic NPM and the increased stability of the ccn2 mRNA during chondrocyte differentiation in vivo. Furthermore, recombinant chicken NPM enhanced the degradation of chimeric RNAs containing the posttranscriptional cis elements in a chicken embryonic fibroblast extract in vitro. It is noteworthy that the RNA destabilization effect by NPM was far more prominent in the cytosolic extract of chondrocytes than in that of fibroblasts, representing a chondrocyte-specific action of NPM. Stimulation by growth factors to promote differentiation changed the subcellular distribution of NPM in chondrocytes, which followed the expected patterns from the resultant change in the ccn2 mRNA stability. Therefore, the present study reveals a novel aspect of NPM as a key player in the posttranscriptional regulation of ccn2 mRNA during the differentiation of chondrocytes.
CCN2/结缔组织生长因子是一种多功能因子，在软骨细胞的生长和分化中起关键作用。鸡ccn2基因不仅在转录水平受到调控，还受到3'非翻译区（3'-UTR）的转录后元件与一种辅助因子之间相互作用的调控。在本研究中，我们鉴定出核仁磷酸蛋白（NPM）（也称为B23）作为这种辅助因子。证实了NPM与该元件的结合，随后的分析揭示了在体内软骨细胞分化过程中，胞质NPM的减少与ccn2 mRNA稳定性的增加之间存在显著相关性。此外，重组鸡NPM在体外鸡胚成纤维细胞提取物中增强了含有转录后顺式元件的嵌合RNA的降解。值得注意的是，NPM对RNA的去稳定作用在软骨细胞的胞质提取物中比在成纤维细胞中更为显著，这代表了NPM的软骨细胞特异性作用。生长因子促进分化的刺激改变了软骨细胞中NPM的亚细胞分布，这与ccn2 mRNA稳定性的相应变化所预期的模式一致。因此，本研究揭示了NPM作为软骨细胞分化过程中ccn2 mRNA转录后调控关键参与者的一个新方面。
