The CDK inhibitor, p27Kip1, is required for IL-4 regulation of astrocyte proliferation.
IL-4 is a pleiotrophic cytokine that has been shown to affect cells of the central nervous system. We have demonstrated that IL-4 inhibits DNA synthesis and proliferation in human astroglia expressing IL-4 receptors. In this study, we sought to identify mechanisms that could account for the antimitogenic effects of IL-4. Epidermal growth factor (EGF)-stimulated human astroglia were arrested in G1 phase by IL-4, even though IL-4 stimulated levels of the G1 cyclins, D1 and E. Histone H1 kinase activity of cdk2 immunoprecipitates, however, was sharply reduced by IL-4; impairment of kinase activity was also evident in cyclin E immunoprecipitates, which contained evidence of hypophosphorylated (inactive) cdk2 product. Reduced cyclin E-associated cdk2 activity was not due to impaired cyclin-dependent kinase-activating kinase (CAK) activity, which was unaffected by IL-4. Inactive cyclin E/cdk2 complexes from IL-4 + EGF-treated cells contained, however, strikingly elevated p27Kip1 cdk inhibitor. Elevated p27 was also detectable in whole cell lysates after 24 and 48 h of IL-4 treatment; by 72 h, p27 was no longer elevated. Pretreatment with antisense but not mismatch p27 oligonucleotides attenuated the inhibitory effects of IL-4 on DNA synthesis and histone kinase activity of cyclin E/cdk2 complexes. Antisense p27 also abrogated IL-4-mediated elevation of p27 in whole cell lysates and cyclin E/cdk2 complexes. These findings demonstrate that IL-4 regulates the cell cycle machinery of astroglial cells via a p27Kip1 braking mechanism.
Liu
J
J
Department of Neurological Surgery, The Cleveland Clinic Foundation, OH 44195, USA.
Flanagan
W M
WM
Drazba
J A
JA
Estes
M L
ML
Barnett
G H
GH
Haqqi
T
T
Kondo
S
S
Barna
B P
BP
D015703:Antigens, CD / Q000378:metabolism; D001253:Astrocytes / Q000378:metabolism / Q000473:pathology*; D018797:Cell Cycle Proteins; D002455:Cell Division / Q000187:drug effects; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D006801:Humans; D015847:Interleukin-4 / Q000235:genetics / Q000494:pharmacology*; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D018123:Receptors, Interleukin / Q000378:metabolism; D019948:Receptors, Interleukin-4; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D015703:Antigens, CD; D018797:Cell Cycle Proteins; D008869:Microtubule-Associated Proteins; D016376:Oligonucleotides, Antisense; D018123:Receptors, Interleukin; D019948:Receptors, Interleukin-4; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D015847:Interleukin-4; D018844:Cyclin-Dependent Kinases