Transforming growth factor-β-mediated p15(INK4B) induction and growth inhibition in astrocytes is SMAD3-dependent and a pathway prominently altered in human glioma cell lines

Jeremy N. Rich*, Ming Zhang, Michael B. Datto, Darell D. Bigner, Xiao Fan Wang

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

97 Scopus citations

Abstract

We sought to characterize the pathway by which the multifunctional cytokine transforming growth factor-β (TGF-β) inhibits the proliferation of normal astrocytes, and we analyzed the alterations in the TGF-β pathway in human glioma cell lines. Upon TGF-β treatment, primary rat astrocytes showed a significant decrease in DNA synthesis upon thymidine incorporation with a cell cycle arrest in the G1 phase. Western analysis of the astrocytes revealed that the expression of the cyclin-dependent kinase inhibitor (CdkI) p15(INK4B) was significantly up-regulated upon TGF-β treatment without a change in other CdkI levels. The retinoblastoma protein (Rb) became hypophosphorylated, and Cdk2 activity decreased. Analysis of Smad3 null mouse astrocytes showed a significant loss of both TGF-β-mediated growth inhibition and p15(INK4B) induction compared with wild-type mouse astrocytes. Infection of rat astrocytes by SMAD3 and SMAD4 adenoviruses failed to induce increased expression of p15(INK4B), implying indirect transcriptional regulation of p15(INK4B) by SMAD3. High-grade human gliomas secrete TGF-β, yet are resistant to its growth inhibitory effects. Analysis of the effects of TGF-β on 12 human glioma cell lines showed that TGF-β mildly inhibited the growth of six lines, had no effect on four lines, and stimulated the growth of two lines. The majority of glioma lines had homozygous deletions of the p15(INK4B) gene, except for two lines that expressed p15(INK4B) protein, which was induced further upon TGF-β treatment. Three lines mildly induced CdkI p21(WAF1) expression in response to TGF-β. Most tumor lines retained other TGF-β-mediated responses, including extracellular matrix protein and angiogenic factor secretion, which may contribute to increased malignant behavior. This suggests that the loss of p15(INK4B) may explain, in part, the selective loss of growth inhibition by TGF-β in gliomas to form a more aggressive tumor phenotype.

Original languageEnglish (US)
Pages (from-to)35053-35058
Number of pages6
JournalJournal of Biological Chemistry
Volume274
Issue number49
DOIs
StatePublished - Dec 3 1999

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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