Altered Cellular Distribution and Subcellular Sorting of γ-Tubulin in Diffuse Astrocytic Gliomas and Human Glioblastoma Cell Lines

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Abstract

Centrosome amplification is a pivotal mechanism underlying tumorigenesis but its role in gliomas is underinvestigated. The present study specifically examines the expression and distribution of the centrosome-associated cytoskeletal protein γ-tubulin in 56 primary diffuse astrocytic gliomas (grades II-IV) and in 4 human glioblastoma cell lines (U87MG, U118MG, U138MG, and T98G). Monoclonal anti-peptide antibodies recognizing epitopes in C-terminal or N-terminal domains of the γ-tubulin molecule were used in immunohistochemical, immunofluorescence, and immunoblotting studies. In tumors in adults (n = 46), varying degrees of localization were detected in all tumor grades, but immunoreactivity was significantly increased in high-grade anaplastic astrocytomas and glioblastomas multiforme as compared to low-grade diffuse astrocytomas (p = 0.0001). A similar trend was noted in diffuse gliomas in children but the sample of cases was too small as to be statistically meaningful. Two overlapping patterns of ectopic cellular localization were identified in both primary tumors and glioblastoma cell lines: A punctate pattern, in which γ-tubulin was partially co-distributed with pericentrin in the pericentriolar region, and a diffuse pattern, independent of pericentrin staining, denoting a soluble pool of γ-tubulin. Cellular γ-tubulin was detected in both soluble and insoluble (nocodazole-resistant) fractions of glioblastoma cells. Divergent localizations of γ-tubulin and pericentrin suggest a differential distribution of these 2 centrosome-associated proteins in glioblastoma cell lines. Our results indicate that overexpression and ectopic cellular distribution of γ-tubulin in astrocytic gliomas may be significant in the context of centrosome protein amplification and may be linked to tumor progression and anaplastic potential.

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