Distribution of the class II beta-tubulin in developmental and adult rat tissues

Intrinsic and Extrinsic Factors Affecting Microtubule Dynamics in Normal and Cancer Cells

Microtubules (MTs), highly dynamic structures composed of α- and β-tubulin heterodimers, are involved in cell movement and intracellular traffic and are essential for cell division. Within the cell, MTs are not uniform as they can be composed of different tubulin isotypes that are post-translationally modified and interact with different microtubule-associated proteins (MAPs). These diverse intrinsic factors influence the dynamics of MTs. Extrinsic factors such as microtubule-targeting agents (MTAs) can also affect MT dynamics. MTAs can be divided into two main categories: microtubule-stabilizing agents (MSAs) and microtubule-destabilizing agents (MDAs). Thus, the MT skeleton is an important target for anticancer therapy. This review discusses factors that determine the microtubule dynamics in normal and cancer cells and describes microtubule-MTA interactions, highlighting the importance of tubulin isoform diversity and post-translational modifications in MTA responses and the consequences of such a phenomenon, including drug resistance development.

Expression of Class II β-Tubulin by Proliferative Myoepithelial Cells in Canine Mammary Mixed Tumors

Benign mammary mixed tumors in dogs resemble human salivary pleomorphic adenomas with regard to their histogenesis, including the occurrence of cartilaginous or bony metaplasia as well as the expression pattern of cytoskeletal proteins in proliferative myoepithelial cells. Recently, a monoclonal antibody specific for class II β-tubulin has been developed. The epitope it recognizes was determined to be the hepta-peptide Glu-Glu-Glu-Glu-Gly-Glu-Asp, which is the common sequence found among the canine, rat, mouse, and human class II β-tubulin-specific regions. We carried out immunohistochemical studies on mammary mixed tumors obtained from three female dogs using this the monoclonal antibody. The antibody to class II β-tubulin reacted intensely with proliferative myoepithelial cells in canine mammary mixed tumors, whereas staining was barely detectable in normal myoepithelial cells surrounding alveoli and alveolar ducts within the tumor and adjacent normal tissue. Proliferative myoepithelial cells also expressed vimentin, but α-smooth muscle actin (αSMA) staining was barely detectable. Immunoblot analysis showed that class II β-tubulin and vimentin were expressed in myoepithelial cell lines prepared from the three mammary mixed tumors. On the other hand, only one cell line, which was negative for αSMA, produced cartilage-specific type II collagen. These results suggest that class II β-tubulin could be a new molecular marker of proliferating myoepithelial cells in canine mammary mixed tumors and that differential expression of cytoskeletal components is associated with cartilaginous metaplasia of proliferative myoepithelial cells in mixed mammary tumors.

Microtubule-associated protein tau promotes neuronal class II β-tubulin microtubule formation and axon elongation in embryonic Xenopus laevis

Compared with its roles in neurodegeneration, much less is known about microtubule-associated protein tau's normal functions in vivo, especially during development. The external development and ease of manipulating gene expression of Xenopus laevis embryos make them especially useful for studying gene function during early development. To study tau's functions in axon outgrowth, we characterized the most prominent tau isoforms of Xenopus embryos and manipulated their expression. None of these four isoforms were strictly analogous to those commonly studied in mammals, as all constitutively contained exon 10, which is preferentially removed from mammalian fetal tau isoforms, as well as exon 8, which in mammals is rare. Nonetheless, like mammalian tau, Xenopus tau exhibited alternative splicing of exon 4a, which in mammals distinguishes 'big' tau of peripheral neurons, and exon 6. Strongly suppressing tau expression with antisense morpholino oligonucleotides only modestly compromised peripheral nerve outgrowth of intact tadpoles, but severely disrupted neuronal microtubules containing class II β-tubulins while leaving other microtubules largely unperturbed. Thus, the relatively mild dependence of axon development on tau likely resulted from having only a single class of microtubules disrupted by its loss. Also, consistent with its greater expression in long peripheral axons, boosting expression of 'big' tau increased neurite outgrowth significantly and enhanced tubulin acetylation more so than did the smaller isoform. These data demonstrate the utility of Xenopus as a tool to gain new insights into tau's functions in vivo.

AP-1-mediated expression of brain-specific class IVa β-tubulin in P19 embryonal carcinoma cells

Expression of brain-specific phenotypes increased in all trans retinoic acid (ATRA)-induced neural differentiation of mouse P19 embryonal carcinoma cells. Among these phenotypes, expression of class IVa β-tubulin isotype (TUBB4a) was particularly enhanced in neural differentiation. Transient transfection assays employing a reporter construct found that ATRA-mediated regulatory region of the TUBB4a gene lay in the region from −83 nt to +137 nt relative to the +1 transcription start site. Site-directed mutagenesis in the AP-1 binding site at −29/−17 suggested that the AP-1 binding site was a critical region for ATRA-mediated TUBB4a expression. Chromatin immunoprecipitation experiments suggested participation of JunD and activating transcription factor-2 (ATF2) in TUBB4a expression. Additionally, exogenous induction of the dominant-negative (dn) type of JunD canceled ATRA-induced upregulation of TUBB4a, and the dn type of ATF2 suppressed even the basal activity. Further immunoblot study revealed an ATRA-mediated increase in JunD protein, while a significant amount of ATF2 protein was constantly produced. These results suggest that differentiation-mediated activation of JunD results in enhanced TUBB4a expression.

Drugs that target dynamic microtubules: a new molecular perspective

Microtubules have long been considered an ideal target for anticancer drugs because of the essential role they play in mitosis, forming the dynamic spindle apparatus. As such, there is a wide variety of compounds currently in clinical use and in development that act as antimitotic agents by altering microtubule dynamics. Although these diverse molecules are known to affect microtubule dynamics upon binding to one of the three established drug domains (taxane, vinca alkaloid, or colchicine site), the exact mechanism by which each drug works is still an area of intense speculation and research. In this study, we review the effects of microtubule-binding chemotherapeutic agents from a new perspective, considering how their mode of binding induces conformational changes and alters biological function relative to the molecular vectors of microtubule assembly or disassembly. These "biological vectors" can thus be used as a spatiotemporal context to describe molecular mechanisms by which microtubule-targeting drugs work.

Chondroid chordoma of the skull base: immunohistochemical and ultrastructural study of two cases with special reference to microtubules within rough-surfaced endoplasmic reticulum

Two cases of skull base chordoma (case 1, a 57-year-old woman; case 2, a 69-year-old woman) were investigated immunohistochemically and ultrastructurally. The tumors showed histopathological features typical of chondroid chordoma and contained both classical chordomatous and hyaline cartilaginous components. Tumor cells were immunoreactive for cytokeratin, vimentin, and S-100 protein, but negative for microtubule-associated protein 2 and class III beta-tubulin (tub-B3). Tumor cells of case 2 were immunoreactive for tau-protein and class II beta-tubulin (tub-B2), whereas those of case 1 were negative. Ultrastructurally, tumor cells in both cases showed the presence of abundant glycogen granules, well-developed intracellular organelles, and desmosome-like junctions. In case 2, several microtubules were closely packed and ran parallel or in random directions within the dilated cisterns of rough-surfaced endoplasmic reticulum (rough ER). "Microtubules within rough ER" has been described in several neoplasms, including classical and chondroid chordomas. Although previous reports documented the tub-B3 immunoreactivity in chordomas, our results suggested that, in our case 2, the predominant isoform of beta-tubulin in microtubules within rough ER was not tub-B3 but tub-B2.

Tumoral and tissue-specific expression of the major human beta-tubulin isotypes

The beta-tubulins are microtubule components encoded by a multigene family, which produces slightly different proteins with complex expression patterns. Several widely used anticancer drugs base their activity on beta-tubulin binding, microtubule dynamics alteration, and cell division blockage. The expression of these drug targets in tumoral and normal cells could be of crucial importance for therapy outcome, unfortunately, the complex beta-tubulin expression patterns have been poorly characterized in human. In this study, we developed a quantitative RT-PCR technique that accurately determines the mRNA expression of the eight human beta-tubulin isotypes, encoding class I, IIa, IIb, III, IVa, IVb, V, and VI and applied it to 21 nontumoral tissues and 79 tumor samples belonging to seven cancer types. In the nontumoral tissues, we found that, overall, TUBB (I), TUBB2C (IVb), and TUBB6 (V) were ubiquitous, TUBB1(VI) was hematopoietic cell-specific, and TUBB2A (IIa), TUBB2B (IIb), TUBB3 (III), and TUBB4 (IVa) had high expression in brain; however, the contribution of the different isotypes to the total beta-tubulin content varied for each tissue and had a complex pattern. In tumoral tissues, most isotypes exhibited an altered expression in specific tumor types or related to tumoral characteristics. In general, TUBB3 showed a great increase in expression while TUBB6 expression was largely decreased in most tumors. Thus, normal tissues showed a complex beta-tubulin isotype distribution, which could contribute to the toxicity profile of the microtubule-binding drugs. In addition, the specific isotypes significantly altered in tumors might represent markers for drug response.

Characterization of anti-beta-tubulin antibodies

Tubulin antibodies are among the most extensively used immunological reagents in basic and applied cell and molecular biology. In this chapter, we provide a brief overview of the practices and reagents developed in our laboratory during the past 25 years for characterizing anti-beta-tubulin antibodies.

Regulation of Class II β-Tubulin Expression by Tumor Suppressor p53 Protein in Mouse Melanoma Cells in Response toVincaAlkaloid

The continuous exposure of antimicrotubule drugs to tumors often results in the emergence of drug-resistant tumor cells with altered expression of several beta-tubulin isotypes. We found that Vinca alkaloid enhanced expression of class II beta-tubulin isotype (mTUBB2) in mouse B16F10 melanoma cells via alteration of the tumor suppressor p53 protein. Vincristine treatment stimulated an increase in mTUBB2 mRNA expression and promoted accumulation of this isotype around the nuclei. Transient transfection assays employing a reporter construct, together with site-directed mutagenesis studies, suggested that the p53-binding site found in the first intron was a critical region for mTUBB2 expression. Electrophoretic mobility shift assay and associated antibody supershift experiments showed that vincristine promoted release of p53 protein from the binding site. In addition, exogenous induction of TAp63gamma (p51A), a homologue of p53, canceled the effect of vincristine on mTUBB2 expression. These results suggest that p53 protein may function as a suppressor of mTUBB2 expression and vincristine-mediated inhibition of p53 binding results in enhanced mTUBB2 expression. This phenomenon could be related with the emergence of drug-resistant tumor cells induced by Vinca alkaloid and may participate in determining the fate of these cells.

Expression of tubulin beta II in neuroepithelial tumors: reflection of architectural changes in the developing human brain

Tubulin beta II (Tub-II) is widely distributed in the developing neuronal axons and dendrites. Recent studies have demonstrated that Tub-II is also important in the early development of the human brain, and Tub-II represents a marker for progenitor and neural stem cells. To elucidate the correlation between the developing brain and neuroepithelial tumors (NETs), the present study assessed Tub-II expression by NETs and normal brain tissue using immunohistochemical and immunoblot analyses. In the gliomas, decreased numbers and staining intensities of Tub-II-positive cells tended to be associated with increased differentiation. Conversely, neuronal neoplasms displayed high percentages and strong staining intensities among the Tub-II-positive cells, irrespective of differentiation. In neuronal neoplasms and neoplasms with neuronal differentiation, Tub-II staining was far more intense and more homogeneous than Tub-II staining in gliomas. These results indicate that the expression of Tub-II in NETs may reflect architectural changes in the developing brain and may support the hypothesis that neuroepithelial tumors originate from glioneuronal progenitor cells capable of generating astrocytic, and neuronal cell types.

Immunohistochemical distribution of tubulin beta II in human normal and neoplastic tissues

Tubulin is the major constituent protein of microtubules. In mammals, there are seven beta-tubulins and six alpha-tubulins. Each beta-tubulin isotype has a unique tissue distribution. The purpose of this study was to describe the distribution of tubulin beta II in normal and neoplastic human tissues with immunohistochemical techniques. We obtained normal tissues from 33 cases (8 fetuses, 17 neonates, 3 children and 5 adults) and 121 samples of neoplastic tissue from surgical specimens or at autopsy. Immunohistochemical staining for tubulin beta II was performed using a monoclonal antibody, KNY379 developed in our laboratory. Tubulin beta II was detected in various normal tissues, particularly in fetal and neonatal tissues, such as the nervous system, pulmonary alveoli, bronchioles and bronchi, colon, pancreatic ducts and acini, renal convoluted tubuli, skin epidermis, body cavity mesothelial cells, smooth muscle and thymus. In the adult, broad expression was also observed; however, the immunoreactivity was weaker and the extent of its distribution decreased with age. In neoplastic tissues, tubulin beta II immunoreactivity was detected in various nervous system neoplasms and other neoplasms such as pancreatic solid cystic carcinoma, pleomorphic adenoma, Warthin's tumor, nephroblastoma, basal cell carcinoma and malignant mesothelioma. We conclude that our monoclonal antibody, KNY379, may be useful as a marker of nervous system neoplasm, pancreatic solid cystic carcinoma, pleomorphic adenoma, Warthin's tumor, nephroblastoma, basal cell carcinoma and malignant mesothelioma.

Morphological characterization of skin ganglion-like cells in Djungarian hamsters (Phodopus sungorus)

Characteristic ganglion-like cell proliferation observed in the skin of Djungarian hamsters was investigated using 24 male and 24 female hamsters, 1-6 months of age, to examine the anatomic location of these ganglion-like cells and their morphologic features. One abdominal skin tumor composed of these cells and resembling proliferative fasciitis in humans was also examined. Skin ganglion-like cells were rarely observed in young animals but increased in number and extent with age, especially in males. These cells were frequently seen in the ventral and medial regions of the trunk and legs rather than in the dorsal and lateral regions. Light microscopic examination of these ganglion-like cells revealed abundant vesicular basophilic cytoplasm with delicate intracytoplasmic silver stain-positive fibrils. Ultrastructurally, these cells contained abundant rough endoplasmic reticulum and Golgi complexes with dilated cisternae; intracellular collagen fibrils were present within these cisternae. Heat shock protein 47, beta-tubulin, and androgen receptor were expressed in these cells. The morphologic features of cells of one tumor resembling human proliferative fasciitis were identical to those observed in ganglion-like cells. The results of the present study suggest that these ganglion-like cells are derived from intrinsic undifferentiated mesenchymal cells in the dermis or subcutaneous adipose tissue and that any tumor-like lesion they form should be regarded as an abnormal proliferative lesion of skin ganglion-like cells rather than as proliferative fasciitis or fibroma.