Article

Identification of mutations that disrupt phosphorylation-dependent nuclear export of cyclin D1

Department of Cancer Biology, The Leonard and Madlyn Abramson Family Cancer Research Institute and Cancer Center, University of Pennsylvania, Philadelphia, PA 19104, USA.
Oncogene (Impact Factor: 8.56). 11/2006; 25(47):6291-303. DOI: 10.1038/sj.onc.1209644
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ABSTRACT Although cyclin D1 is overexpressed in a significant number of human cancers, overexpression alone is insufficient to promote tumorigenesis. In vitro studies have revealed that inhibition of cyclin D1 nuclear export unmasks its neoplastic potential. Cyclin D1 nuclear export depends upon phosphorylation of a C-terminal residue, threonine 286, (Thr-286) which in turn promotes association with the nuclear exportin, CRM1. Mutation of Thr-286 to a non-phosphorylatable residue results in a constitutively nuclear cyclin D1 protein with significantly increased oncogenic potential. To determine whether cyclin D1 is subject to mutations that inhibit its nuclear export in human cancer, we have sequenced exon 5 of cyclin D1 in primary esophageal carcinoma samples and in cell lines derived from esophageal cancer. Our work reveals that cyclin D1 is subject to mutations in primary human cancer. The mutations identified specifically disrupt phosphorylation of cyclin D1 at Thr-286, thereby enforcing nuclear accumulation of cyclin D1. Through characterization of these mutants, we also define an acidic residue within the C-terminus of cyclin D1 that is necessary for recognition and phosphorylation of cyclin D1 by glycogen synthase kinase-3 beta. Finally, through construction of compound mutants, we demonstrate that cell transformation by the cancer-derived cyclin D1 alleles correlates with their ability to associate with and activate CDK4. Our data reveal that cyclin D1 is subject to mutations in primary human cancer that specifically disrupt phosphorylation-dependent nuclear export of cyclin D1 and suggest that such mutations contribute to the genesis and progression of neoplastic growth.

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    • "For example, no consistent association of cyclin D1 amplification was found with response to therapeutic challenge in patients with hormone receptor-positive breast cancer (Lundgren et al, 2012; Rudas et al, 2008). Furthermore, mutations within the coding region of cyclin D1, found in cases of esophageal and endometrial cancer (Moreno-Bueno et al, 2003; Benzeno et al, 2006), have yet to be associated with clinical markers of disease progression, together suggesting that the observed oncogenic functions of cyclin D1 involve additional mechanisms of deregulation. Consistent with this concept, emerging clinical evidence suggests that alternative splicing of cyclin D1 transcript (cyclin D1a) to the shorter isoform cyclin D1b occurs frequently in human malignancy (Augello et al, 2014; Musgrove et al, 2011; Wang et al, 2008; Comstock et al, 2009), and appears to be a major mechanism though which cyclin D1 exerts its oncogenic activity. "
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    • "Furthermore, expression of exogenous wild type as well as phospho-mimetic S12E Fbx4 decreased steady-state cyclin D1 levels in TE8 cells with low endogenous Fbx4 activity (Figure 1e). As a negative control, expression of Fbx4 in TE7 cells (in which cyclin D1 is not efficiently exported to the cytoplasm (Benzeno et al., 2006) did not affect cyclin D1 levels. Taken together, these data suggest that expression of Fbx4 exerts a tumor suppressive effect in human cancer cells through regulation of cyclin D1. "
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    Oncogene 01/2011; 30(17):1995-2002. DOI:10.1038/onc.2010.584 · 8.56 Impact Factor
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    • "Cyclin D1 is subject to intricate posttranslational control to ensure its temporal regulation. Cyclin D1 nuclear export followed by Fbx4-dependent ubiquitylation and degradation during S-phase are key features that serve to restrain nuclear cyclin D1/CDK4 activity and ensure normal cell division (Alt et al., 2000; Benzeno et al., 2006; Lin et al., 2006). Previous work revealed that aberrant nuclear accumulation of cyclin D1 during S-phase promotes transformation in vitro (Alt et al., 2000) and drives both B cell lymphomas and mammary carcinomas in mice (Gladden et al., 2006; Lin et al., 2008). "
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