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Antagonist effect of insulin-like growth
factor I on protein kinase inhibitor-mediated apoptosis in human glioblastoma
cells in association with bcl-2 and bcl-xL
Toms SA, Hercbergs A, Liu J, Kondo S, Haqqi T, Casey G, Iwasaki K, Barnett
GH, Barna BP
Department of Neurological Surgery, The Cleveland Clinic
Foundation, Ohio, USA
Object. Tamoxifen (TAM) has been found to be effective in inhibiting
proliferation of glioblastoma cells in vitro, but clinical studies have been
disappointing.
The purpose of this study was to determine whether insulin-like growth factor I
(IGF-I), a potential autocrine/paracrine mitogen produced by glioblastomas,
interferes with the antimitogenic actions of TAM.
Methods. Human glioblastoma cells were treated with or
without TAM and/or IGF-I in vitro and evaluated for: viability by the
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenol tetrazolium bromide cleavage assay;
apoptosis by histochemical analysis of nuclear morphology and 3'-OH DNA
fragments; and expression of the IGF-I receptor, and the bcl-2, bcl-xL, and bax
proteins by immunoblot analysis.
In addition, p53 status was determined by DNA sequencing and by transient
transfection with luciferase reporter plasmids containing wild-type or mutant
p53.
Results indicated that after 72 hours of exposure to 2 mg/ml TAM in vitro, 56.3%
of WITG3 and 43.8% of U87-MG glioblastoma cells contained apoptotic nuclei (p
< 0.01 compared with untreated cells).
Apoptosis was independent of the presence of p53 because the WITG3 cells, in
contrast to the U87-MG cells, expressed a mutant, nonfunctional p53.
The WITG3 cells expressed IGF-I receptor proteins and demonstrated IGF-I
binding.
Exogenous IGF-I stimulated WITG3 cell proliferation and significantly (p <
0.05) antagonized the cytotoxic effects of TAM in a dose-dependent fashion;
IGF-I, but not TAM, enhanced expression of bcl-2 and bcl-xL proteins; however,
bax protein expression was unchanged by either treatment.
Conclusions. Because many gliomas secrete large amounts
of IGF-I in autocrine/paracrine growth pathways, these data may, in part,
explain the failure of TAM to achieve clinical results as dramatic as those in
vitro.
PMID: 9576258 [PubMed - indexed for MEDLINE]
Source: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=9576258&dopt=Abstract
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