title: NPDC-1, a novel regulator of neuronal proliferation, is degraded by the ubiquitin/proteasome system through a PEST degradation motif.
abstract: Neural proliferation and differentiation control protein-1 (NPDC-1) is a protein expressed primarily in brain and lung and whose expression can be correlated with the regulation of cellular proliferation and differentiation. Embryonic differentiation in brain and lung has classically been linked to retinoid signaling, and we have recently characterized NPDC-1 as a regulator of retinoic acid-mediated events. Regulators of differentiation and development are themselves highly regulated and usually through multiple mechanisms. One such mechanism, protein degradation via the ubiquitin/proteasome degradation pathway, has been linked to the expression of a number of proteins involved in control of proliferation or differentiation, including cyclin D1 and E2F-1. The data presented here demonstrate that NPDC-1 is likewise degraded by the ubiquitin/proteasome system. MG-132, a proteasome inhibitor, stabilized the expression of NPDC-1 and allowed detection of ubiquitinated NPDC-1 in vivo. A PEST motif (rich in proline, glutamine, serine, and threonine) located in the carboxyl terminus of NPDC-1 was shown to target the protein for degradation. Deletion of the PEST motif increased NPDC-1 protein stability and NPDC-1 inhibitory effect on retinoic acid-mediated transcription. NPDC-1 was phosphorylated by several kinases, including extracellular signal-regulated kinase. Phosphorylation of NPDC-1 increased the in vitro rate of NPDC-1 ubiquitination. The MEK inhibitor, PD-98059, an inhibitor of extracellular signal-regulated activation, also inhibited the formation of ubiquitinated NPDC-1 in vivo. Together these results suggest that retinoic acid signaling can be modulated by the presence of NPDC-1 and that the protein level and activity of NPDC-1 can be regulated by phosphorylation-mediated proteasomal degradation.
authors.affiliation: Department of Molecular and Cellular Biochemistry, University of Kentucky Medical Center, 800 Rose Street, Lexington, KY 40536, USA.
authors.forename: Michael L
authors.initials: ML
authors.lastname: Spencer
authors.forename: Maria
authors.initials: M
authors.lastname: Theodosiou
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Noonan
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D001921:Brain / Q000196:embryology; D018797:Cell Cycle Proteins / Q000378:metabolism; D002454:Cell Differentiation; D002455:Cell Division; D019938:Cyclin D1 / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism; D008168:Lung / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000378:metabolism*; D016716:PC12 Cells; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D011499:Protein Processing, Post-Translational; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D051381:Rats; D012176:Retinoids / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D014212:Tretinoin / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D018797:Cell Cycle Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; C493755:E2f1 protein, rat; D004791:Enzyme Inhibitors; D005419:Flavonoids; D008164:Luminescent Proteins; D009097:Multienzyme Complexes; C484270:NPDC1 protein, human; D009419:Nerve Tissue Proteins; C092313:Npdc1 protein, mouse; D011500:Protein Synthesis Inhibitors; D012176:Retinoids; D014157:Transcription Factors; D025801:Ubiquitin; D019938:Cyclin D1; D049452:Green Fluorescent Proteins; D014212:Tretinoin; D003513:Cycloheximide; D020928:Mitogen-Activated Protein Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one