Proteomic identification of glutamine synthetase as a differential marker for oligodendrogliomas and astrocytomas
Laboratory investigation
Object
Astrocytomas and oligodendrogliomas are primary CNS tumors that remain a challenge to differentiate histologically because of their morphological variability and because there is a lack of reliable differential diagnostic markers. To identify proteins that are differentially expressed between astrocytomas and oligodendrogliomas, the authors analyzed the proteomic expression patterns and identified uniquely expressed proteins in these neoplasms.
Methods
Proteomes of astrocytomas and oligodendrogliomas were analyzed using 2D gel electrophoresis and subsequent computerized gel analysis to detect differentially expressed proteins. The proteins were identified using high-performance liquid chromatography accompanied by tandem mass spectrometry. To determine the role of the differentially expressed proteins in astrocytes, undifferentiated glial cell cultures were treated with dibutyryl–cyclic adenosine monophosphate (cAMP).
Results
Two-dimensional gel electrophoresis revealed that glutamine synthetase was differentially expressed in astrocytomas and oligodendrogliomas. Western blot and immunohistochemical analyses confirmed the increased expression of glutamine synthetase in astrocytomas compared with oligodendrogliomas. Whereas glutamine synthetase expression was demonstrated across all grades of astrocytomas (Grade II–IV [15 tumors]) and oligoastrocytomas (4 tumors), it was expressed in only 1 oligodendroglioma (6% [16 tumors]). Treatment of undifferentiated glial cell cultures with dibutyryl-cAMP resulted in astrocyte differentiation that was associated with increased levels of glial fibrillary acidic protein and glutamine synthetase.
Conclusions
These data indicate that glutamine synthetase expression can be used to distinguish astrocytic from oligodendroglial tumors and may play a role in the pathogenesis of astrocytomas.
Abbreviations used in this paper:
cAMP = cyclic adenosine monophosphate; GFAP = glial fibrillary acidic protein; HPLC = high-performance liquid chromatography; PAGE = polyacrylamide gel electrophoresis; SDS = sodium dodecyl sulfate.
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