Characterization of nuclear β_II‐tubulin in tumor cells: A possible novel target for taxol

Abstract

As the subunits of microtubules, alpha- and beta-tubulins have been thought to only exist in the cytoplasm where they are incorporated into microtubules. However, the beta(II) isotype of tubulin has recently been observed in the nuclei of rat kidney mesangial cells [Walss et al., 1999: Cell Motil. Cytoskeleton 42:274-284]. In this study, we detected nuclear beta(II)-tubulin in rat C6 glioma cells, human T98G glioma cells, human MCF-7 breast carcinoma cells, human MDA-MB-435 breast carcinoma cells, and human Hela cervix carcinoma cells. In addition, nuclear beta(II)-tubulin in these cells was found to exist as alphabeta(II) dimers instead of assembled microtubules and appeared to be particularly concentrated in the nucleoli. Several anti-tubulin drugs were used to treat C6 cells to determine their influence on nuclear beta(II)-tubulin. Taxol, a tubulin drug with higher specificity for beta(II)-tubulin than for other beta-tubulin isotypes, irreversibly decreased nuclear beta(II) content in a concentration-dependent manner in C6 cells. Meanwhile, cells were found to be apoptotic as was suggested by the presence of multiple micronuclei and DNA fragmentation. On the other hand, no depletion of nuclear beta(II)-tubulin was observed when C6 cells were incubated with colchicine or nocodazole, two anti-tubulin drugs with higher specificity for the alphabeta(IV) isotype, supporting the hypothesis that drugs with higher specificity for beta(II)-tubulin deplete nuclear beta(II)-tubulin.

Cytoskeleton and paclitaxel sensitivity in breast cancer: The role of β‐tubulins

“…11,21,22 We verified this hypothesis analyzing a panel of cell lines and a series of patients treated with taxol.…”

Hsp70 dynamics in vivo: effect of heat shock and protein aggregation

“…might be indirectly involved in the immobilization of the GFPHsp70(K71E). We found nocodazole increased the mobility of the GFP-Hsp70(K71E) in the cytosol and surprisingly also increased its mobility in the nucleus (data not shown), even though polymerized microtubules are thought not to be present in the nucleoplasm (Walss-Bass et al, 2002;Walss-Bass et al, 2001;Xu and Luduena, 2002). We also found that treatment of heat-shocked cells expressing GFP-Hsp70(K71E) with DTT caused a significant decrease in the amount of immobilized GFP-Hsp70(K71E) in about 25% of the cells (data not shown).…”

Chromatin maintenance by a molecular motor protein

“…move along. While there is some evidence for tubulin and short, possibly, branched, networks of actin 36,37 in the nucleus, it remains to be determined whether KIF4 interacts with these structures. Since KIF4 physically interacts with lamin A, an intriguing, yet untested, possibility is that KIF4 uses the lamins as a track.…”