Retinoic acid decreases targeting of p27 for degradation via an N-myc-dependent decrease in p27 phosphorylation and an N-myc-independent decrease in Skp2.
Poor prognosis neuroblastoma (NB) tumors are marked by amplification and overexpression of N-myc. Retinoic acid (RA) decreases N-myc levels and induces cell cycle arrest in vitro and increases event-free survival in advanced stage NB patients. In this study, we investigated the mechanism(s) by which RA regulates cell cycle and how N-myc affects NB cell cycle progression. Constitutive N-myc overexpression stimulates increases in cyclin E-dependent kinase activity and decreases in p27 resulting in increased DNA synthesis. N-myc regulates p27 levels through an increase in targeting of p27 to the proteasome via cyclin E kinase-dependent phosphorylation of p27 and its ubiquitination. N-myc also stimulates an increase in proteasome activity. In RA-treated cells in which N-myc levels decline as p27 levels increase, degradation of p27 is also decreased. However, RA does not affect the activity of proteasome. The decrease in the degradation of p27 in RA-treated cells is due in part to a decrease in the N-myc stimulated phosphorylation of p27. However, RA also decreases Skp2 levels thus impairing the ability of p27 to be ubiquitinated. Thus, RA induces both N-myc-dependent and -independent mechanisms to minimize the degradation of p27 and arrest NB cell growth.
Nakamura
M
M
Cell and Molecular Biology Section, Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
Matsuo
T
T
Stauffer
J
J
Neckers
L
L
Thiele
C J
CJ
D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D019927:Cyclin E; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases / Q000187:drug effects / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D006801:Humans; D008840:Microfilament Proteins / Q000378:metabolism*; D009097:Multienzyme Complexes / Q000378:metabolism; D009124:Muscle Proteins; D009447:Neuroblastoma / Q000235:genetics / Q000473:pathology; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D016271:Proto-Oncogene Proteins c-myc / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism; D044786:S-Phase Kinase-Associated Proteins / Q000187:drug effects / Q000378:metabolism*; D014212:Tretinoin / Q000494:pharmacology*; D014452:Ubiquitins / Q000378:metabolism
D018797:Cell Cycle Proteins; D019927:Cyclin E; D008840:Microfilament Proteins; D009097:Multienzyme Complexes; D009124:Muscle Proteins; D016271:Proto-Oncogene Proteins c-myc; D044786:S-Phase Kinase-Associated Proteins; C058992:Tagln protein, mouse; D014452:Ubiquitins; D014212:Tretinoin; C495911:CDK6 protein, human; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex