FIGURE 4.

Cell cycle phase-specific down-regulation of α- and β-tubulin by WA treatment. A, representative flow histograms depicting cell cycle phase-specific expression of α-tubulin in MCF-7 cells treated with DMSO or 2 μm WA (24-h treatment). B, cell cycle phase-specific quantitation of α-tubulin is shown in the bar graph. C, representative flow histograms depicting cell cycle phase-specific expression of β-tubulin in MCF-7 cells treated with DMSO or 2 μm WA (24-h treatment). D, cell cycle phase-specific quantitation of β-tubulin is shown in the bar graph. Data represent means ± S.D. (n = 3). Statistical significance was determined by Student's t test. E, real-time quantitative RT-PCR for mRNA levels of α- and β₁-tubulin (upper and lower panels, respectively) in MCF-7 and SUM159 cells after a 24-h treatment with DMSO or the indicated concentrations of WA. Data represent means ± S.D. (n = 3). **, significantly different (p < 0.01) compared with the DMSO-treated control by one-way analysis of variance, followed by Dunnett's test. F, Western blotting for α- and β-tubulin using lysates from MCF-7 cells treated for 24 h with WA and/or MG132 (2-h pretreatment). The numbers on top of the bands represent the change in protein levels relative to the DMSO-treated control. Each experiment was repeated with comparable results.