Overexpression of mRNA-binding protein CRD-BP in malignant melanomas

Abstract

Wnt/b-catenin signaling pathway plays an important role in embryogenesis, stem cell maintenance, tumorigenesis and aging. Here, we show that RNA-binding protein, coding region determinant-binding protein (CRD-BP) (a transcriptional target of Wnt signaling pathway), is highly expressed in primary human malignant melanomas and melanoma cell lines with activated Wnt/b-catenin signaling pathway. Upregulation of CRD-BP is associated with an elevated level of b-TrCP1 ubiquitin ligase receptor and activation of nuclear transcriptional factors-kappa B (NF-jB) signaling. Knockdown of CRD-BP inhibits NF-jB activity, induces apoptosis, and suppresses proliferation and tumorigenic properties of melanoma cells. Keywords: CRD-BP; b-TrCP; mRNA stability; melanoma; Wnt/b-catenin signaling; NF-kB The increased incidence of cutaneous melanoma in the past three decades, its highly progressive nature and resistance to treatment, has prompted enhanced attention to this disease (reviewed in Chin et al., 2006;Herlyn, 2006). Despite numerous studies conducted on melanocytic lesions, the molecular mechanisms of melanoma development and progression are still poorly understood.Wnt/b-catenin signaling plays an important role in normal development and stem cells maintenance, whereas its aberrant upregulation is involved in tumorigenesis (Giles et al., 2003;Weeraratna, 2005). The defining events of an active canonical Wnt pathway include accumulation of cytoplasmic b-catenin, its subsequent nuclear translocation and initiation of bcatenin/Tcf-dependent transcription. In the absence of WNT, abundance and transcriptional activity of b-catenin is regulated by the large multicomponent machinery that includes adenomatous polyposis coli protein (APC), axin, CK1 and glycogen synthase kinase 3-b. This complex facilitates phosphorylation of bcatenin and determines its subsequent degradation. Binding of WNT ligand with its Frizzled and lowdensity lipoprotein receptor-related protein (5/6) receptors starts a cascade of events that results in disruption of b-catenin phosphorylation, subsequent accumulation of free b-catenin in the cytoplasm, its nuclear translocation and transcriptional activation of target genes. Overexpression of WNT proteins, mutations in APC and/or stabilizing b-catenin mutations are the most common alterations associated with constitutively upregulated Wnt signaling and tumor development. Nuclear localization of b-catenin, the hallmark of an active canonical Wnt pathway, was observed in approximately 30% of primary and metastatic human melanoma samples (Rimm et al., 1999).Activation of nuclear transcriptional factors-kappa B (NF-kB) is frequently observed in various types of human tumors, including melanoma (Basseres and Baldwin, 2006;Gilmore, 2006). In many cells, the major NF-kB heterodimer is composed of p50 and RelA/p65 subunits that are responsible for activation of canonical NF-kB signaling. The inhibitors of NF-kB (IkBs) tightly regulate activity of p50/RelA dimer. The IkBs bind to NF-kB dimers and block their nuclear locali...

MicroRNA-340-mediated Degradation of Microphthalmia-associated Transcription Factor mRNA Is Inhibited by the Coding Region Determinant-binding Protein

“…Furthermore, we set out to decipher the role of a RNA-binding protein, coding region determinantbinding protein (CRD-BP, IMP-1, IGF2BP1) in the regulation of MITF. This protein has been shown to attenuate miRNA-dependent degradation of different mRNA (21) and has also been found to be overexpressed in melanoma (24). Our results showed that CRD-BP restricts the action of miR-340 by preventing its access to the mRNA of MITF, thereby proposing a novel mode of regulation of MITF.…”

“…As discussed earlier, CRD-BP protects another mRNA from miRNA-mediated destabilization (21). Moreover, CRD-BP has also been shown to be overexpressed in melanoma cell lines and human melanoma samples contributing to oncogenesis (24). Knockdown of CRD-BP in 451Lu cells decreased the level of endogeneous MITF mRNA by more than 5-fold (Fig.…”

“…c-myc, ␤TrCP1, Gli1, etc.). We have also shown previously that CRD-BP is overexpressed in the majority of malignant melanomas (24). However, knockdown of CRD-BP in melanoma cells had a much more robust effect than in other tumor cells, and hence involvement of an additional melanoma specific factor was hypothesized.…”

IGF2BP1 (insulin-like growth factor 2 mRNA binding protein 1)

“…Disease IGF2BP1 is highly expressed in primary human malignant melanomas and melanoma cell line (Elcheva et al, 2008).…”

Towards identifying New Human Ribonucleases that Cleave microRNA Using a High-Throughput Method.

“…The c-myc coding region determinant-binding protein (CRD-BP) is another example of RBP found highly expressed in various types of human cancer including breast, colon, skin, ovary, lung, brain and testicular cancer (Doyle et al, 2000;Ioannidis et al, 2003;Dimitriadis et al, 2007;Ross et al, 2001;Kobel et al, 2007;Hammer et al, 2005;Ioannidis et al, 2005;Elcheva et al, 2008;Ioannidis et al, 2004). CRD-BP has been…”