Article
Inhibition of the EGFR/MAPK pathway in glioblastoma cell lines at different points of application – inhibition of EGFR's tyrosine kinase via gefitinib causes a depression of PTPIP51
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Authors
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M. Petri
- Institute of Anatomy and Cell Biology, Justus-Liebig-University, Giessen, Germany
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J. Planz
- Institute of Anatomy and Cell Biology, Justus-Liebig-University, Giessen, Germany
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U. Nestler
- Department of Neurosurgery, Justus-Liebig-University, Giessen, Germany
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A. Stenzinger
- Institute of Pathology, University Hospital, Heidelberg, Germany
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A. Paradowska
- Department of Urology and Pediatric Urology, Justus-Liebig-University, Giessen, Germany
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M. Wimmer
- Institute of Anatomy and Cell Biology, Justus-Liebig-University, Giessen, Germany
| Published: | April 28, 2011 |
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Outline
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Objective: Protein tyrosine phosphatase interacting protein 51 (PTPIP51) is an interaction partner of 14-3-3β, which correlates with the grade of malignancy in gliomas. PTPIP51 expression is described in various carcinomas. Its overexpression was shown to enhance apoptosis in HeLa cells. The EGFR is overexpressed in about 40 to 50% of cases of glioblastoma multiforme (GBM), and almost half of these co-express the mutant receptor subtype EGFRvIII. In this study PTPIP51 and its correlation with the EGFR/MAPK pathway by 14-3-3β was investigated in cell lines of GBM.
Methods: Cell lines from five GBM patients and U87 were treated by gefitinib, cetuximab and PD98059 with different times and concentrations. To compare different mRNA expression levels of PTPIP51 and 14-3-3β after inhibition of the EGFR/MAPK pathway, quantitative RT-PCR was used. The metabolism rate of the tumor cells during examination was probed by the Alamar blue test with ELISA. We measured the changes in the expression profiles and determined the co-localization of 14-3-3β and PTPIP51 with the interacting partners PTP1B, c-Src and Raf-1 pathway by immunohistochemistry.
Results: The inhibition of the EGFR tyrosine kinase by gefitinib led to a decreased mRNA expression of PTPIP51 and 14-3-3β, which was correlated to their lower protein levels as observed by immunostaining. The cell number and cell metabolism were reduced. Inhibition of EGFR and EGFRvIII by cetuximab as well as the inhibition of the MAP kinase by PD98059 did not lead to significant changes in PTPIP51 mRNA expression levels in all cell lines.
Conclusions: The EGFR signalling cascade via the MAPK pathway is modulated by PTP1B through c-Src and by 14-3-3β through Raf-1, both interacting partners of PTPIP51 and co-localized with PTPIP51 in GBM. However, in GBM cell lines, the inhibition of the EGFR’s intracellular tyrosine kinase does have a decreasing effect on PTPIP51 expression. Further studies should explore the prognostic relevance of PTPIP51 in therapeutic decisions concerning EGFR targeting drugs in GBM.
