Downregulation of Skp2 and p27/Kip1 synergistically induces apoptosis in T98G glioblastoma cells.
S-phase kinase associated protein (Skp) 2 is an F-box protein required for substrate recognition of the SCF(Skp2) ubiquitin ligase complex. Skp2 is often overexpressed in transformed cells and in various types of tumors. Downregulation or inhibition of Skp2 inhibits growth of breast cancer cells and small-cell lung carcinoma cells. We downregulated Skp2 in T98G glioblastoma cells using small interfering RNA (siRNA). Downregulation induced p27 and caused growth arrest and apoptosis. Downregulation of both Skp2 and p27 increased apoptosis synergistically. Cyclin E levels and cyclin E-CDK2 kinase activity increased dramatically when both Skp2 and p27 were downregulated. Coincidently, Bcl-2 but not Bcl-xL expression decreased, and caspase-3 was activated. Inhibition of cyclin E-CDK2 kinase activity by forced expression of p21 reversed these effects. Moreover, stable expression of Bcl-2 also abrogated apoptosis induced by downregulation of Skp2 and p27. We suggest that Skp2 in tumor cells suppresses apoptosis through Bcl-2 expression, potentially through regulation of cyclin E-CDK2 activity.
Lee
Sang Hyun
SH
Cancer Research Institute and Comprehensive Cancer Center, University of California, San Francisco, CA 94143, USA.
McCormick
Frank
F
D017209:Apoptosis / Q000502:physiology*; D042846:CDC2-CDC28 Kinases / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D049109:Cell Proliferation; D016543:Central Nervous System Neoplasms / Q000378:metabolism / Q000473:pathology*; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D015536:Down-Regulation; D005909:Glioblastoma / Q000378:metabolism / Q000473:pathology*; D006133:Growth Substances / Q000378:metabolism; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D051020:bcl-X Protein
C494811:BCL2L1 protein, human; C436291:CDKN1B protein, human; D002352:Carrier Proteins; D019927:Cyclin E; D006133:Growth Substances; D047908:Intracellular Signaling Peptides and Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D044786:S-Phase Kinase-Associated Proteins; D051020:bcl-X Protein; D050760:Cyclin-Dependent Kinase Inhibitor p27; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases