Drugs affecting microtubule dynamics increase alpha-tubulin mRNA accumulation via transcription in Tetrahymena thermophila

Alpha-Tubulin Acetylation in Trypanosoma cruzi: A Dynamic Instability of Microtubules Is Required for Replication and Cell Cycle Progression

Trypanosomatids have a cytoskeleton arrangement that is simpler than what is found in most eukaryotic cells. However, it is precisely organized and constituted by stable microtubules. Such microtubules compose the mitotic spindle during mitosis, the basal body, the flagellar axoneme and the subpellicular microtubules, which are connected to each other and also to the plasma membrane forming a helical arrangement along the central axis of the parasite cell body. Subpellicular, mitotic and axonemal microtubules are extensively acetylated in Trypanosoma cruzi. Acetylation on lysine (K) 40 of α-tubulin is conserved from lower eukaryotes to mammals and is associated with microtubule stability. It is also known that K40 acetylation occurs significantly on flagella, centrioles, cilia, basal body and the mitotic spindle in eukaryotes. Several tubulin posttranslational modifications, including acetylation of K40, have been cataloged in trypanosomatids, but the functional importance of these modifications for microtubule dynamics and parasite biology remains largely undefined. The primary tubulin acetyltransferase was recently identified in several eukaryotes as Mec-17/ATAT, a Gcn5-related N-acetyltransferase. Here, we report that T. cruzi ATAT acetylates α-tubulin in vivo and is capable of auto-acetylation. TcATAT is located in the cytoskeleton and flagella of epimastigotes and colocalizes with acetylated α-tubulin in these structures. We have expressed TcATAT with an HA tag using the inducible vector pTcINDEX-GW in T. cruzi. Over-expression of TcATAT causes increased levels of the alpha tubulin acetylated species, induces morphological and ultrastructural defects, especially in the mitochondrion, and causes a halt in the cell cycle progression of epimastigotes, which is related to an impairment of the kinetoplast division. Finally, as a result of TcATAT over-expression we observed that parasites became more resistant to microtubule depolymerizing drugs. These results support the idea that α-tubulin acetylation levels are finely regulated for the normal progression of T. cruzi cell cycle.

Selectively high efficacy of eribulin against high-grade invasive recurrent and/or metastatic squamous cell carcinoma of the head and neck

Patients with recurrent and/or metastatic squamous cell carcinoma of the head and neck (R/M SCCHN) have a poor prognosis. Over the past decade, a major development in the first-line treatment of R/M SCCHN was the introduction of cetuximab in combination with platinum plus 5-fluorouracil chemotherapy. Currently, a promising novel treatment option in R/M SCCHN has emerged, termed immune checkpoint inhibitors. However, only a few patients presenting with R/M SCCHN have exhibited meaningful tumor regression with these agents. Therefore, novel agents are required to order improve the overall survival of patients with R/M SCCHN. Recently, we demonstrated that R/M SCCHN cells are highly sensitive to eribulin. In the present study, the effects of eribulin, paclitaxel and vinblastine were investigated in R/M SCCHN (OLC-01 and OSC-19) and locally advanced SCCHN (OSC-20) cells. Tumour-inhibitory activities of eribulin against R/M SCCHN were evaluated in orthotopic xenograft models. The data revealed that eribulin has sub-nM growth inhibitory activities in vitro against OLC-01 cells, and that it is more potent than paclitaxel and vinblastine. The reduced expression of Tubulin Beta 3 Class III (TUBB3) following treatment was correlated with a high sensitivity to eribulin. Histological analysis of OLC-01 cells in NOD-SCID mice demonstrated that they had a higher invasiveness in the tissue around the alveolar cancer when compared with the histology of OSC-19 cells, which has been reported in our previous study. Treatment with eribulin revealed marked inhibitory activities in vivo at 0.125 mg/kg against OLC-01 cells orthotopic xenografts. In conclusion, the results highlight the existence of invasive-type heterogeneity in R/M SCCHN with respect to eribulin sensitivity. Eribulin is already an approved clinical agent; therefore, the continued investigation of its preclinical antitumor attributes may contribute significantly to the future process of identifying novel uses of eribulin against R/M SCCHN.

Gene expression profiling reveals epithelial mesenchymal transition (EMT) genes can selectively differentiate eribulin sensitive breast cancer cells

OBJECTIVES

Eribulin mesylate is a synthetic macrocyclic ketone analog of the marine sponge natural product halichondrin B. Eribulin is a mechanistically unique inhibitor of microtubule dynamics. In this study, we investigated whether selective signal pathways were associated with eribulin activity compared to paclitaxel, which stabilizes microtubules, based on gene expression profiling of cell line panels of breast, endometrial, and ovarian cancer in vitro.

RESULTS

We determined the sets of genes that were differentially altered between eribulin and paclitaxel treatment in breast, endometrial, and ovarian cancer cell line panels. Our unsupervised clustering analyses revealed that expression profiles of gene sets altered with treatments were correlated with the in vitro antiproliferative activities of the drugs. Several tubulin isotypes had significantly lower expression in cell lines treated with eribulin compared to paclitaxel. Pathway enrichment analyses of gene sets revealed that the common pathways altered between treatments in the 3 cancer panels were related to cytoskeleton remodeling and cell cycle regulation. The epithelial-mesenchymal transition (EMT) pathway was enriched in genes with significantly altered expression between the two drugs for breast and endometrial cancers, but not for ovarian cancer. Expression of genes from the EMT pathway correlated with eribulin sensitivity in breast cancer and with paclitaxel sensitivity in endometrial cancer. Alteration of expression profiles of EMT genes between sensitive and resistant cell lines allowed us to predict drug sensitivity for breast and endometrial cancers.

CONCLUSION

Gene expression analysis showed that gene sets that were altered between eribulin and paclitaxel correlated with drug in vitro antiproliferative activities in breast and endometrial cancer cell line panels. Among the panels, breast cancer provided the strongest differentiation between eribulin and paclitaxel sensitivities based on gene expression. In addition, EMT genes were predictive of eribulin sensitivity in the breast and endometrial cancer panels.

Mechanistic studies of semicarbazone triapine targeting human ribonucleotide reductase in vitro and in mammalian cells: tyrosyl radical quenching not involving reactive oxygen species

Triapine® (3-aminopyridine-2-carboxaldehyde thiosemicarbazone (3-AP)) is a drug in Phase II trials. One of its established cellular targets is the β(2) subunit of ribonucleotide reductase that requires a diferric-tyrosyl-radical [(Fe(III)(2)-Y·)(Fe(III)(2))] cofactor for de novo DNA biosynthesis. Several mechanisms for 3-AP inhibition of β(2) have been proposed; one involves direct iron chelation from β(2), whereas a second involves Y· destruction by reactive oxygen species formed in situ in the presence of O(2) and reductant by Fe(II)-(3-AP). Inactivation of β(2) can thus arise from cofactor destruction by loss of iron or Y·. In vitro kinetic data on the rates of (55)Fe and Y· loss from [((55)Fe(III)(2)-Y·)((55)Fe(III)(2))]-β(2) under aerobic and anaerobic conditions reveal that Y· loss alone is sufficient for rapid β(2) inactivation. Oxyblot(TM) and mass spectrometric analyses of trypsin-digested inhibited β(2), and lack of Y· loss from H(2)O(2) and O(2)(•) treatment together preclude reactive oxygen species involvement in Y· loss. Three mammalian cell lines treated with 5 μm 3-AP reveal Y· loss and β(2) inactivation within 30-min of 3-AP-exposure, analyzed by whole-cell EPR and lysate assays, respectively. Selective degradation of apo- over [(Fe(III)(2)-Y·)(Fe(III)(2))]-β(2) in lysates, similar iron-content in β(2) immunoprecipitated from 3-AP-treated and untreated [(55)Fe]-prelabeled cells, and prolonged (12 h) stability of the inhibited β(2) are most consistent with Y· loss being the predominant mode of inhibition, with β(2) remaining iron-loaded and stable. A model consistent with in vitro and cell-based biochemical studies is presented in which Fe(II)-(3-AP), which can be cycled with reductant, directly reduces Y· of the [(Fe(III)(2)-Y·)(Fe(III)(2))] cofactor of β(2).

Microtubule-interacting drugs induce moderate and reversible damage to human bone marrow mesenchymal stem cells

OBJECTIVES

This study aimed to investigate molecular and cellular changes induced in human bone marrow mesenchymal stem cells (hMSCs) after treatment with microtubule-interacting agents and to estimate damage to the bone marrow microenvironment caused by chemotherapy.

MATERIALS AND METHODS

Using an in vitro hMSC culture system and biochemical and morphological approaches, we studied the effect of nocodazole and taxol(R) on microtubule and nuclear envelope organization, tubulin and p53 synthesis, cell cycle progression and proliferation and death of hMSCs isolated from healthy donors.

RESULTS AND CONCLUSIONS

Both nocodazole and taxol reduced hMSC proliferation and induced changes in the microtubular network and nuclear envelope morphology and organization. However, they exhibited only a moderate effect on cell death and partial arrest of hMSCs at G(2) but not at M phase of the cell cycle. Both agents induced expression of p53, exclusively localized in abnormally shaped nuclei, while taxol, but not nocodazole, increased synthesis of beta-tubulin isoforms. Cell growth rates and microtubule and nuclear envelope organization gradually normalized after transfer, in drug-free medium. Our data indicate that microtubule-interacting drugs reversibly inhibit proliferation of hMSCs; additionally, their cytotoxic action and effect on microtubule and nuclear envelope organization are moderate and reversible. We conclude that alterations in human bone marrow cells of patients under taxol chemotherapy are transient and reversible.

Katanin regulates dynamics of microtubules and biogenesis of motile cilia

The in vivo significance of microtubule severing and the mechanisms governing its spatial regulation are not well understood. In Tetrahymena, a cell type with elaborate microtubule arrays, we engineered null mutations in subunits of the microtubule-severing complex, katanin. We show that katanin activity is essential. The net effect of katanin on the polymer mass depends on the microtubule type and location. Although katanin reduces the polymer mass and destabilizes the internal network of microtubules, its activity increases the mass of ciliary microtubules. We also show that katanin reduces the levels of several types of post-translational modifications on tubulin of internal and cortical microtubules. Furthermore, katanin deficiencies phenocopy a mutation of β-tubulin that prevents deposition of polymodifications (glutamylation and glycylation) on microtubules. We propose that katanin preferentially severs older, post-translationally modified segments of microtubules.

Gene-specific signal transduction between microtubules and tubulin genes in Tetrahymena thermophila

Mammalian cells regulate tubulin mRNA abundance by a posttranscriptional mechanism dependent on the concentration of tubulin monomer. Treatment of mammalian cells with microtubule-depolymerizing drugs and microtubule-polymerizing drugs causes decreases and increases in tubulin mRNA, respectively (D. W. Cleveland, Curr. Opin. Cell Biol. 1:10-14, 1989). In striking contrast to the case with mammalian cells, perturbation of microtubules in Tetrahymena thermophila by microtubule-depolymerizing or -polymerizing drugs increases the level of the single alpha-tubulin gene message by increasing transcription (L. A. Stargell, D. P. Heruth, J. Gaertig, and M. A. Gorovsky, Mol. Cell. Biol. 12:1443-1450, 1992). In this report we show that antimicrotubule drugs preferentially induce the expression of one of two beta-tubulin genes (BTU1) in T. thermophila. In contrast, deciliation induces expression of both beta-tubulin genes. Tubulin gene expression was examined in a mutant strain created by transformation with an in vitro-mutagenized beta-tubulin gene that conferred resistance to microtubule-depolymerizing drugs and sensitivity to the polymerizing drug taxol and in a strain containing a nitrosoguanidine-induced mutation in the single alpha-tubulin gene that conferred the same pattern of drug sensitivities. In both cases the levels of tubulin mRNA expression from the drug-inducible BTU1 gene in the mutant cells paralleled the altered growth sensitivities to microtubule drugs. These studies demonstrate that T. thermophila has distinct, gene-specific mechanisms for modulating tubulin gene expression depending on whether ciliary or cytoplasmic microtubules are involved. They also show that the cytoplasmic microtubule cytoskeleton itself participates in a signal transduction pathway that regulates specific tubulin gene transcription in T. thermophila.

Structure-function analysis of antimicrotubule dinitroanilines against promastigotes of the parasitic protozoan Leishmania mexicana

Although leishmaniasis is a major tropical disease, the currently available drugs are toxic and inadequate. We show that the antimicrotubule herbicide trifluralin has antileishmania activity. The present study aimed at deducing the relationship between the structure of the molecule and its antiprotozoan activity. Nine dinitroanilines, all of which were analogs of trifluralin, were compared. We found that pendimethalin was 2.5-fold more potent than trifluralin, and the higher efficacy may be correlated with molecular structural features that increase the accessibility to one nitro group. This association was further supported by molecular modeling. Moreover, trifluralin samples from two sources differed in their activities by more than threefold, and gas column chromatography showed that impurities were present in the more potent sample.