Overexpression of γ-tubulin in non-small cell lung cancer

Abstract

We and others have previously shown that increased expression and altered compartmentalization of γ-tubulin may contribute to tumorigenesis and tumor progression (J. Cell Physiol. 2009;223:519-529; Cancer Biol. Ther. 2010;9:66-76). Here we have determined by immunohistochemistry the localization and cellular distribution of γ-tubulin in clinical tissue samples from 109 non-small cell lung cancer (NSCLC) cases. The expression and distribution of γ-tubulin protein and transcripts was also determined in the NSCLC tumor cell lines NCI-H460 (HTB-177) and NCI-H69 (HTB-119) by immunocytochemistry, quantitative immunoblotting and reverse transcription quantitative real-time PCR (RT-qPCR). Polyclonal and monoclonal anti-peptide antibodies recognizing epitopes in the C- or N-terminal domains of γ-tubulins and human gene-specific primers for γ-tubulins 1 (TUBG1) and 2 (TUBG2) were used. In non-neoplastic cells of the airway epithelium in situ, γ-tubulin exhibited predominantly apical surface and pericentriolar localizations. In contrast, markedly increased, albeit heterogeneous and variously prominent γ-tubulin immunoreactivity was detected in clinical tumor specimens and in the NCI-H460 and NCI-H69 cell lines, where tumor cells exhibited overlapping multi-punctate and diffuse patterns of localization. Co-expression of γ-tubulin and Ki-67 (MIB-1) was detected in a population of proliferating tumor cells. A statistically significant increase of γ-tubulin expression was found in Stage III compared to lesser stage tumors (p<0.001 v. Stages I/II) regardless of histological subtype or grade. By quantitative immunoblotting NCI-H460 and NCI-H69 cells expressed higher levels of γ-tubulin protein compared to small airway epithelial cells (SAEC). In both tumor cell lines increase in TUBG1 and TUBG2 transcripts was detected by RT-qPCR. Our results reveal for the first time an increased expression of γ-tubulin in lung cancer