J. Cell Commun. Signal. (2009) 3:85–86 DOI 10.1007/s12079-009-0039-5 BITS AND BYTES Hijacking ZIP codes: posttanscriptional regulation of CCN2 by nucleophosmin Andrew Leask Received: 19 November 2008 / Accepted: 5 February 2009 / Published online: 18 February 2009 # The Author(s) 2009. This article is published with open access at Springerlink.com Abstract CCN2 (connective tissue growth factor [CTGF]/ hypertrophic chondrocyte-specific gene product 24 [Hcs24]) is regulated at the transcriptional and posttran- scriptional level. For example, an element in the its 3′ untranslated region (3′-UTR) of the CCN2 mRNA controls message stability in chondrocytes. In a recent study, Mukudai et al. (Mol Cell Biol 28:6134-6147, 2008) purified and identified a trans-factor protein binding to the minimal repressive cis element in the 3′-UTR of ccn2 mRNA and identify this protein as the multifunctional nucleolar phosphoprotein nucleophosmin (NPM) This commentary summarizes these observations. Keywords CTGF . CCN2 . UTR . Nucleophosmin CCN2 (connective tissue growth factor [CTGF]/hypertro- phic chondrocyte-specific gene product 24 [Hcs24]) is a cysteine-rich secretory protein of 36 to 38 kDa that has four distinct modules; that is, the insulin-like growth factor- binding protein-like, von Willebrand factor type C repeat, thrombospondin type 1 repeat, and C-terminal modules (Leask and Abraham 2006). Although the regulation of CCN2 has been principally found to occur at the level of gene transcription (Grotendorst et al. 1996; Holmes et al. 2001; This commentary is also available in the Newsletter section of the CCN Society website http://ccnsociety.com/ A. Leask Canadian Institutes of Health Research Group in Skeletal Development and Remodeling, Division of Oral Biology, London, ON, Canada N6A 5C1 A. Leask (*) Department of Physiology and Pharmacology, Schulich School of Medicine & Dentistry, The University of Western Ontario, London, ON, Canada N6A 5C1 e-mail: andrew.leask@schulich.uwo.ca Leask et al. 2001), it has also been established that, inc chondrocytes, the CCN2 gene can also be regulated by elements in its 3′ untranslated region (3′-UTR) at posttran- scriptional stages (Kondo et al. 2000). Indeed, a cis element in the 3′-UTR of chicken ccn2 mRNA plays an important role in CCN2 regulation in chondrocytes (Mukodai et al. 2005). The 3′ UTR has for quite some time been recognized as being responsible for positioning mRNAs in particular portions of the cell and hence controlling the location of RNA translation, especially in terms of the Drosophila oocyte (Macdonald and Struhl 1988; Macdonald et al. 1993). It is now accepted that the 3′ UTR is generally required for placing mRNAs in subcellular compartments, and hence acts as a sort of ZIP code containing specific cis elements which can bind trans-acting factors which act to position mRNAs in cells. Such mechanisms involve the use of molecular motors such as dynein to shuttle mRNAs along microtubules (Epstein et al. 2000). Nucleophosmin (NPM) is an abundantly expressed multifunctional nucleolar phosphoprotein. A unified mech- anism for NPM’s role in cell growth has recently been proposed; namely, that NPM directs the nuclear export of both 40S and 60S ribosomal subunits (Maggi et al. 2008). Transduction of NPM shuttling-defective mutants or loss of Npm1, inhibits nuclear export of both the 40S and 60S ribosomal subunits, reduces the available pool of cytoplas- mic polysomes, and diminishes overall protein synthesis without affecting rRNA processing or ribosome assembly. In a recent report, Mukudai et al. (2008) finally purified and identified this trans-factor protein binding the minimal repressive cis element in the 3′-UTR of ccn2 mRNA as NPM. With recombinant NPM protein, the authors were able to reproduce the posttranscriptional regulatory events in vitro that were observed during endochondral ossification in vivo. Alteration of nucleocytoplasmic shuttling of the trans factor