Differential expression and cellular distribution of gamma-tubulin and betaIII-tubulin in medulloblastomas and human medulloblastoma cell lines

Abstract

In previous studies, we have shown overexpression and ectopic subcellular distribution of gamma-tubulin and betaIII-tubulin in human glioblastomas and glioblastoma cell lines (Katsetos et al., 2006, J Neuropathol Exp Neurol 65:455-467; Katsetos et al., 2007, Neurochem Res 32:1387-1398). Here we determined the expression of gamma-tubulin in surgically excised medulloblastomas (n = 20) and in the human medulloblastoma cell lines D283 Med and DAOY. In clinical tissue samples, the immunohistochemical distribution of gamma-tubulin labeling was pervasive and inversely related to neuritogenesis. Overexpression of gamma-tubulin was widespread in poorly differentiated, proliferating tumor cells but was significantly diminished in quiescent differentiating tumor cells undergoing neuritogenesis, highlighted by betaIII-tubulin immunolabeling. By quantitative real-time PCR, gamma-tubulin transcripts for TUBG1, TUBG2, and TUBB3 genes were detected in both cell lines but expression was less prominent when compared with the human glioblastoma cell lines. Immunoblotting revealed comparable amounts of gamma-tubulin and betaIII-tubulin in different phases of cell cycle; however, a larger amount of gamma-tubulin was detected in D283 Med when compared with DAOY cells. Interphase D283 Med cells exhibited predominantly diffuse cytoplasmic gamma-tubulin localization, in addition to the expected centrosome-associated distribution. Robust betaIII-tubulin immunoreactivity was detected in mitotic spindles of DAOY cells. Our data indicate that overexpression of gamma-tubulin may be linked to phenotypic dedifferentiation (anaplasia) and tumor progression in medulloblastomas and may potentially serve as a promising tumor marker.