The mitotic kinase Aurora--a promotes distant metastases by inducing epithelial-to-mesenchymal transition in ERα(+) breast cancer cells.

In this study, we demonstrate that constitutive activation of Raf-1 oncogenic signaling induces stabilization and accumulation of Aurora-A mitotic kinase that ultimately drives the transition from an epithelial to a highly invasive mesenchymal phenotype in estrogen receptor α-positive (ERα(+)) breast cancer cells. The transition from an epithelial- to a mesenchymal-like phenotype was characterized by reduced expression of ERα, HER-2/Neu overexpression and loss of CD24 surface receptor (CD24(-/low)). Importantly, expression of key epithelial-to-mesenchymal transition (EMT) markers and upregulation of the stemness gene SOX2 was linked to acquisition of stem cell-like properties such as the ability to form mammospheres in vitro and tumor self-renewal in vivo. Moreover, aberrant Aurora-A kinase activity induced phosphorylation and nuclear translocation of SMAD5, indicating a novel interplay between Aurora-A and SMAD5 signaling pathways in the development of EMT, stemness and ultimately tumor progression. Importantly, pharmacological and molecular inhibition of Aurora-A kinase activity restored a CD24(+) epithelial phenotype that was coupled to ERα expression, downregulation of HER-2/Neu, inhibition of EMT and impaired self-renewal ability, resulting in the suppression of distant metastases. Taken together, our findings show for the first time the causal role of Aurora-A kinase in the activation of EMT pathway responsible for the development of distant metastases in ERα(+) breast cancer cells. Moreover, this study has important translational implications because it highlights the mitotic kinase Aurora-A as a novel promising therapeutic target to selectively eliminate highly invasive cancer cells and improve the disease-free and overall survival of ERα(+) breast cancer patients resistant to conventional endocrine therapy.

Phase I trial of autologous hematopoietic SCT with escalating doses of topotecan combined with CY and carboplatin in patients with relapsed or persistent ovarian or primary peritoneal carcinoma.

We designed a phase I clinical trial of escalating doses of topotecan with CY and carboplatin in combination with autologous hematopoietic SCT (AHSCT) for the treatment of relapsed or persistent platinum sensitive ovarian or primary peritoneal carcinoma. After stem cell collection, 16 patients received topotecan at 1.5, 2.5, 3.5, 4.5 or 6.0 mg/m(2)/d combined with CY 1.5 g/m(2)/d and carboplatin 200 mg/m(2)/d, all by 4-day continuous infusion. Steady state pharmacokinetics of topotecan and carboplatin were examined. Pre-treatment biopsies were examined for the expression of topoisomerase (topo) I, Ki67 and Bcl-2 family members by immunohistochemistry. One of six patients at a topotecan dose of 4.5 mg/m(2)/d and two of three patients at 6.0 mg/m(2)/d had dose-limiting toxicity of grade 3 stomatitis lasting >2 weeks. There was no treatment-related mortality. As topotecan clearance was constant over the dose range examined, topotecan steady state plasma concentrations increased with dose. Median progression-free survival and overall survival were 6.5 months and 2.7 years, respectively. Shorter progression-free survival was observed in tumors with low topo expression (P=0.04). Topotecan can safely be dose escalated to 4.5 mg/m(2)/d in combination with CY, carboplatin and AHSCT. This trial is registered at ClinicalTrials.gov as NCT00652691.

Methods for the analysis of centrosome reproduction in cancer cells.

The assay described here allows a direct comparison of centrosome function (i.e., MT nucleation capacity) between normal and tumor tissues. It can be applied to samples such as human tissues in which the materials are limited. The assay is rapid and uses equipment commonly available. Comparison of the ability of individual centrosomes to nucleate microtubules within the context of tissues can provide novel insight into the disease process itself. In the example shown here, tumor tissues nucleate significantly greater numbers of microtubules from single or amplified centrosomes in comparison to normal tissue. The increased microtubule nucleation capacity from multiple centrosomes seen in tumors may be related to the increased frequency of mitotic aberrations and to the loss of cell and tissue architecture that is seen in cancer. This assay can also be used to characterize the microtubule nucleation capacity of normal tissues, during development and aging, and in disease states other than cancer where microtubule dynamics may play an important role.

The mitotic checkpoint protein hBUB3 and the mRNA export factor hRAE1 interact with GLE2p-binding sequence (GLEBS)-containing proteins.

The mRNA export factor RAE1 (also called GLE2) and the mitotic checkpoint protein BUB3 share extensive sequence homology in yeast as well as higher eukaryotes, although the biological relevance of their similarity is unclear. Previous work in HeLa cells has shown that human (h)RAE1 binds the nuclear pore complex protein hNUP98 via a short NUP98 motif called GLEBS (for GLE2p-binding sequence). Here we report that the two known binding partners of hBUB3, the mitotic checkpoint proteins hBUB1 and hBUBR1, both carry a region with remarkable similarity to the GLEBS motif of hNUP98. We show that the GLEBS-like motifs of mouse (m)BUB1 and mBUBR1 are sufficient for mBUB3 binding. mBUB3 lacks affinity for the hNUP98 GLEBS, demonstrating its binding specificity for GLEBS motifs of mitotic checkpoint proteins. Interestingly, mRAE1 does not exclusively bind to the GLEBS motif of hNUP98 and can cross-interact with the mBUB1 GLEBS. We show that full-length RAE1 and BUB1 proteins interact in mammalian cells and accumulate both at the kinetochores of prometaphase chromosomes. Our findings demonstrate that GLEBS motifs reside in mammalian nucleoporins and mitotic checkpoint proteins and apparently serve as specific binding sites for either BUB3, RAE1, or both.

Phosphorylation of centrin during the cell cycle and its role in centriole separation preceding centrosome duplication.

Once during each cell cycle, mitotic spindle poles arise by separation of newly duplicated centrosomes. We report here the involvement of phosphorylation of the centrosomal protein centrin in this process. We show that centrin is phosphorylated at serine residue 170 during the G(2)/M phase of the cell cycle. Indirect immunofluorescence staining of HeLa cells using a phosphocentrin-specific antibody reveals intense labeling of mitotic spindle poles during prophase and metaphase of the cell division cycle, with diminished staining of anaphase and no staining of telophase and interphase centrosomes. Cultured cells undergo a dramatic increase in centrin phosphorylation following the experimental elevation of PKA activity, suggesting that this kinase can phosphorylate centrin in vivo. Surprisingly, elevated PKA activity also resulted intense phosphocentrin antibody labeling of interphase centrosomes and in the concurrent movement of individual centrioles apart from one another. Taken together, these results suggest that centrin phosphorylation signals the separation of centrosomes at prophase and implicates centrin phosphorylation in centriole separation that normally precedes centrosome duplication.

Altered centrosome structure is associated with abnormal mitoses in human breast tumors.

Centrosomes are the major microtubule organizing center in mammalian cells and establish the spindle poles during mitosis. Centrosome defects have been implicated in disease and tumor progression and have been associated with nullizygosity of the p53 tumor suppressor gene. In the present ultrastructural analysis of 31 human breast tumors, we found that centrosomes of most tumors had significant alterations compared to centrosomes of normal breast tissue. These alterations in included 1) supernumerary centrioles, 2) excess pericentriolar material, 3) disrupted centriole barrel structure, 4) unincorporated microtubule complexes, 5) centrioles of unusual length, 6) centrioles functioning as ciliary basal bodies, and 7) mispositioned centrosomes. These alterations are associated with changes in cell polarity, changes in cell and tissue differentiation, and chromosome missegregation through multipolar mitoses. Significantly, the presence of excess pericentriolar material was associated with the highest frequency of abnormal mitoses. Centrosome abnormalities may confer a mutator phenotype to tumors, occasionally yielding cells with a selective advantage that emerge and thrive, thus leading the tumor to a more aggressive state.

Centrosomes and cancer.

The centrosome functions as the major microtubule organizing center (MTOC) of the cell and as such it determines the number, polarity, and organization of interphase and mitotic microtubules. Cytoplasmic organization, cell polarity and the equal partition of chromosomes into daughter cells at the time of cell division are all dependent on the normal function of the centrosome and on its orderly duplication, once and only once, in each cell cycle. Malignant tumor cells show characteristic defects in cell and tissue architecture and in chromosome number that can be attributed to inappropriate centrosome behavior during tumor progression. In this review, we will summarize recent observations linking centrosome defects to disruption of normal cell and tissue organization and to chromosomal instability found in malignant tumors.

Microtubule nucleating capacity of centrosomes in tissue sections.

We used a novel adaptation of methods for microtubule polymerization in vitro to assess the MTOC activity of centrosomes in frozen-sectioned tissues. Remarkably, centrosomes of tissue sections retain the ability to nucleate microtubules even after several years of storage as frozen tissue blocks. Adaptations of these methods allow accurate counts of microtubules from individual cells and the quantitative estimation the MTOC activity of the intact tissue. These methods can be utilized to characterize MTOC activity in normal and diseased tissues and in particular tissues at different stages of development. (J Histochem Cytochem 47:1265-1273, 1999)

Centrosome hypertrophy in human breast tumors: implications for genomic stability and cell polarity.

The centrosome plays an important role in maintenance of cell polarity and in progression through the cell cycle by determining the number, polarity, and organization of interphase and mitotic microtubules. By examining a set of 35 high grade human breast tumors, we show that centrosomes of adenocarcinoma cells generally display abnormal structure, aberrant protein phosphorylation, and increased microtubule nucleating capacity in comparison to centrosomes of normal breast epithelial and stromal tissues. These structural and functional centrosome defects have important implications for understanding the mechanisms by which genomic instability and loss of cell polarity develop in solid tumors.

A novel immediate early response gene, IEX-1, is induced by ultraviolet radiation in human keratinocytes.

Skin cancer is the most common human malignancy and is strongly associated with exposure to ultraviolet radiation (UVR). Several mechanisms including an increase in immediate early gene activation have been postulated to be involved in UVR-mediated carcinogenesis. We show that in a dose-dependent manner, UVR induces the expression of messenger RNA of a novel immediate early response gene, IEX-1, in human keratinocytes. Human keratinocytes and mouse fibroblasts transfected with an expression plasmid for IEX-1 grow at a faster rate than keratinocytes transfected with a similar plasmid that does not contain the IEX-1 sequence. IEX-1 protein is localized predominantly in the nucleus of keratinocytes by fluorescent antibody methods and by examination of the location of a green fluorescence IEX-1 fusion protein. Epidermal growth factor (EGF), a major mitogen of keratinocytes, and a tumor-promoting phorbol ester increase IEX-1 mRNA expression. IEX-1 may play a role in keratinocyte proliferation especially following UVR.

A transformation-associated complex involving tyrosine kinase signal adapter proteins and caldesmon links v-erbB signaling to actin stress fiber disassembly.

The avian erythroblastosis viral oncogene (v-erbB) encodes a receptor tyrosine kinase that possesses sarcomagenic and leukemogenic potential. We have expressed transforming and nontransforming mutants of v-erbB in fibroblasts to detect transformation-associated signal transduction events. Coimmunoprecipitation and affinity chromatography have been used to identify a transformation-associated, tyrosine phosphorylated, multiprotein complex. This complex consists of Src homologous collagen protein (Shc), growth factor receptor binding protein 2 (Grb2), son of sevenless (Sos), and a novel tyrosine phosphorylated form of the cytoskeletal regulatory protein caldesmon. Immunofluorescence localization studies further reveal that, in contrast to the distribution of caldesmon along actin stress fibers in normal fibroblasts, caldesmon colocalizes with Shc in plasma membrane blebs in transformed fibroblasts. This colocalization of caldesmon and Shc correlates with actin stress fiber disassembly and v-erbB-mediated transformation. The tyrosine phosphorylation of caldesmon, and its association with the Shc-Grb2-Sos signaling complex directly links tyrosine kinase oncogenic signaling events with cytoskeletal regulatory processes, and may define one mechanism regulating actin stress fiber disassembly in transformed cells.

Centrin and the cytoskeleton of the protist Holomastigotoides.

The cytoskeleton of the parabasalid protozoan Holomastigotoides was investigated by epifluorescence, scanning confocal, and transmission electron microscopy using antibodies to centrin, tubulin, and MPM-2 epitopes. Previous microscopic analysis of Holomastigotoides spp. has shown that up to 10,000 flagella are arranged in 2-8 spiral bands encircling the cell. Spindle poles are associated with two flagellar bands. Sheets of cytoplasmic microtubules (MTs) called axostyles originate in the cell apex and extend to the cell base. Antibodies to centrin, a member of the EF-hand family of calcium-binding proteins, labeled a number of structures in Holomastigotoides, namely axostyles, the mitotic spindle, and portions of flagellar bands. The identity of these structures was confirmed by transmission electron microscopy and by immunofluorescence microscopy using antibodies to tubulin and MPM-2 epitopes. Antibodies to tubulin labeled MTs in basal bodies, flagella, axostyles, and the mitotic spindle. MPM-2 antibodies labeled spindle poles and short segments of flagellar bands to which the spindle poles are attached. Centrin is known to show calcium-sensitive contractile behavior. The pattern of flagellar band staining by antibodies to centrin was affected by [Ca2+]. In detergent-extracted cell fragments, the centrin staining pattern could be changed by changing [Ca2+]. This Ca2+ effect was modulated by a monoclonal antibody to centrin (20H5), indicating that centrin plays a role in altering flagellar band structure. These results show that centrin is located in key positions for maintaining cell polarity and directing cell movement through interactions with other cytoskeletal elements. Calcium may regulate the morphology of centrin-containing structures.

Lignocellulolysis by ascomycetes (fungi) of a saltmarsh grass (smooth cordgrass).

Lignocellulose (LC) makes up greater than 70% of the mature shoots of the prodigiously photosynthetically productive saltmarsh grass Spartina alterniflora. Naturally decaying shoots of this cordgrass were examined by transmission electron microscopy (after high-pressure freezing and freeze-substitution) as a means of directly detecting lysis of the LC-rich tissues. Portions of the cordgrass were selected that contained ascomata (sexual reproductive structures) of only one of each of four species of fungi (Kingdom Fungi; Subdivision Ascomycotina): Phaeosphaeria spartinicola and Buergenerula spartinae from leaf blades, Phaeosphaeria spartinae from leaf sheaths, and Passeriniella obiones from naked stems. All four of the ascomycetes were LC-lytic. Phaeosphaeria spartinicola caused both thinning of LC-rich secondary walls of fiber cells from cell lumina outwards (type 2 soft rot, akin to white rot) and digestion extending from hyphae within longitudinal cavities in the secondary walls (type 1 soft rot). The other three species caused either one or the other type of soft rot. Bacterial erosion of cordgrass cells was found only in the samples of naked stems. Ascomycetous decomposers of standing-dead grasses may have potential for biotechnological applications involving alterations of lignocellulose or toxic polyphenolic substances.

Cellular Concentrations and Uniformity of Cell-Type Accumulation of Two Lea Proteins in Cotton Embryos.

The levels and cell-type distribution of late embryogenesis abundant (Lea) proteins D-7 and D-113 have been determined in mature cotton embryos by immunochemical methods. The two proteins were expressed in and purified from Escherichia coli and utilized for antibody production in rabbits. The antiserum to each protein was found to interact with all members of each protein family in cotton extracts by protein gel blotting. Using these antibodies in quantitative "rocket" immunoelectrophoreses, D-7 proteins were found to accumulate to ~8 x 1015 molecules per embryo, which is equivalent to ~109 molecules per "average cell." D-113 proteins accumulate to ~1016 molecules per embryo, which equates to ~1.3 x 109 molecules per average cell. These values calculate to concentrations of about 226 and 283 [mu]M, respectively, in the cell aqueous phase immediately prior to seed desiccation. In immunocytochemical studies using the fluorophor rhodamine linked to the secondary antibody, both proteins appeared to be evenly present in the cytosol of all cell types present in the embryo, including both cotyledon and axis epidermal cells. Thus, their function does not appear related to unique functions of specific cell or tissue types. The very high molar concentrations of the two proteins, coupled with their unusual predicted structure and their cytosol location, would seem to reduce the number of their conceivable functions.

Regulatable endogenous production of cytokinins up to 'toxic' levels in transgenic plants and plant tissues.

The effects of expressing a chimeric gene consisting of a soybean heat shock gene promoter and a sequence that encodes an enzyme catalyzing the synthesis of a potent phytohormone, the cytokinin iPMP, have been analyzed in transgenic tobacco plants. The production of cytokinin endogenously produced several effects previously undocumented. The differentiation of shoots independent of exogenous cytokinin from heat-treated transgenic plant leaf explants demonstrates that long-term heat treatments do not interfere with complex developmental processes. This extends the potential usefulness of heat shock gene promoters to conditionally express genes during windows of development that span several weeks.

Visualization of bioluminescence as a marker of gene expression in rhizobium-infected soybean root nodules.

The linked structural genes lux A and lux B, encoding bacterial luciferase of a marine bacterium Vibrio harveyi, were fused with the nitrogenase nifD promoter from Bradyrhizobium japonicum and with the P1 promoter of pBR322. Both fusions were integrated into the B. japonicum chromosome by site-specific recombination. Soybean roots infected with the two types of rhizobium transconjugants formed nitrogen-fixing nodules that produced bright blue-green light. Cells containing the P1 promoter/lux AB fusion resulted in continuously expressed bioluminescence in both free-living rhizobium and in nodule bacteriods. However, when under control of the nifD promoter, luciferase activity was found only in introgen-fixing nodules. Light emission from bacteroids allowed us to visualize and to photograph nodules expressing this marker gene fusion in vivo at various levels of resolution, including within single, living plant cells. Localization of host cells containing nitrogen-fixing bacteroids within nodule tissue was accomplished using low-light video microscopy aided by realtime image processing techniques developed specifically to enhance extreme low-level luminescent images.