Measurement of DNA synthesis by flow cytometry

XB130 mediates cancer cell proliferation and survival through multiple signaling events downstream of Akt

XB130, a novel adaptor protein, mediates RET/PTC chromosome rearrangement-related thyroid cancer cell proliferation and survival through phosphatidyl-inositol-3-kinase (PI3K)/Akt pathway. Recently, XB130 was found in different cancer cells in the absence of RET/PTC. To determine whether RET/PTC is required of XB130-related cancer cell proliferation and survival, WRO thyroid cancer cells (with RET/PTC mutation) and A549 lung cancer cells (without RET/PTC) were treated with XB130 siRNA, and multiple Akt down-stream signals were examined. Knocking-down of XB130 inhibited G₁-S phase progression, and induced spontaneous apoptosis and enhanced intrinsic and extrinsic apoptotic stimulus-induced cell death. Knocking-down of XB130 reduced phosphorylation of p21Cip1/WAF1, p27Kip1, FOXO3a and GSK3β, increased p21Cip1/WAF1protein levels and cleavages of caspase-8 and-9. However, the phosphorylation of FOXO1 and the protein levels of p53 were not affected by XB130 siRNA. We also found XB130 can be phosphorylated by multiple protein tyrosine kinases. These results indicate that XB130 is a substrate of multiple protein tyrosine kinases, and it can regulate cell proliferation and survival through modulating selected down-stream signals of PI3K/Akt pathway. XB130 could be involved in growth and survival of different cancer cells.

XB130, a novel adaptor protein, promotes thyroid tumor growth

Adaptor proteins with multimodular structures can participate in the regulation of various cellular functions. We have cloned a novel adaptor protein, XB130, which binds the p85α subunit of phosphatidyl inositol 3-kinase and subsequently mediates signaling through RET/PTC in TPC-1 thyroid cancer cells. In the present study, we sought to determine the role of XB130 in the tumorigenesis in vivo and in related molecular mechanisms. In WRO thyroid cancer cells, knockdown of XB130 using small interfering RNA inhibited G(1)-S phase progression, induced spontaneous apoptosis, and enhanced intrinsic and extrinsic apoptotic stimulus-induced cell death. Growth of tumors in nude mice formed from XB130 shRNA stably transfected WRO cells were significantly reduced, with decreased cell proliferation and increased apoptosis. Microarray analysis identified 246 genes significantly changed in XB130 shRNA transfected cells. Among them, 57 genes are related to cell proliferation or survival, including many transcription regulators. Ingenuity Pathway Analysis showed that the top-ranked disease related to XB130 is cancer, and the top molecular and cellular functions are cellular growth and proliferation and cell cycle. A human thyroid tissue microarray study identified expression of XB130 in normal thyroid tissue as well as in human thyroid carcinomas. These observations suggest that the expression of XB130 in these cancer cells may affect cell proliferation and survival by controlling the expression of multiple genes, especially transcription regulators.

Transcriptional regulation of differentiation, selective toxicity and ATGCAAAT binding of bisbenzimidazole derivatives in human melanoma cells

To study the relationship between the structure of minor groove ligands and their affinity for specific DNA sequences that regulate gene transcription, three analogues of the A-T-specific DNA minor groove ligands Hoechst 33258 and Hoechst 33342 were synthesized with 5, 8 or 12 carbons in an aliphatic chain attached to the phenolic oxygen of the molecule. There was a striking bimodal relationship between toxicity to HeLa cells and the lipophilicity of the five analogues, toxicity being low for the compounds with a free hydroxyl (Hoechst 33258) or a 12-carbon substituent, yet high for the 5-carbon analogue. Selective killing of human melanoma cells compared with normal fibroblasts was observed for the Hoechst analogue with a 12-carbon chain attached. Hoechst 33258 itself was selectively toxic for the MM96E melanoma cell line compared with other cell lines, induced a highly dendritic morphology, increased tyrosinase activity and tyrosinase mRNA but decreased the level of gp75 (TRP-1) mRNA; message for a third pigment gene, Pmel-17, was unchanged. Tyrosinase activity was decreased in the resistant A2058 melanoma cell line and transcription was affected to a lesser extent than in MM96E. Expression of gp75 protein and two intermediate filament proteins was inhibited by Hoechst 33258 in MM96E cells. There was no major difference in the amount of 125I-Hoechst 33258 taken up by sensitive and resistant cells. Of the five derivatives studied, the parent drug Hoechst 33258 and the 2-carbon analogue (Hoechst 33342) were found to have the most inhibitory effect on affinity of octamer binding proteins for the ATGCAAAT consensus sequence found in the promoter region of certain genes associated with proliferation and differentiation. In contrast to Distamycin A (also an A-T-specific minor groove ligand), Hoechst 33258 displaced proteins already bound to the octamer motif. The G-C ligand chromomycin A3 exhibited a different spectrum of cell toxicity and tyrosinase stimulation compared with Hoechst 33258. Chromomycin A3 but not Hoechst 33258, strongly inhibited the zinc-dependent transcriptional activity of the sheep metallothionein-Ia promoter in reporter gene assays of transfected cells. Since the six metal-responsive elements of the promoter are GC-rich, this provides independent evidence for the sequence-specificity of transcriptional inactivation by one of these drugs in melanoma cells. Overall, the results suggest that Hoechst 33258 acts by inhibiting the transcription of specific genes, cell lines evidently differing in the accessibility to drugs of certain A-T-rich sequences.

Method for kinetic analysis of drug-induced cell cycle perturbations

A method is described for quantitative study of the flux of cells through the cell cycle phases in in vitro systems perturbed by chemicals, such as chemotherapeutic agents. The method utilizes cell count and the flow cytometric technique of bromodeoxyuridine (BrdUrd) labeling, according to an optimized strategy. Cells are exposed to BrdUrd during the last minutes of drug treatment and fixed for analysis at 0, 1/3Ts, 2/3Ts, Ts, and Tc + TG1 recovery times, where Ts, TG1, Tc are the mean durations of phases S and G1 and of the whole cycle of control cells. As an example of application of the proposed procedure, a kinetic study of the effect of 1-(2-chloroethyl)-1-nitrosourea (CNU) on the L1210 cell cycle is described. Simple data analysis, requiring only a pocket calculator, showed that cells in phases G1 and G2M at the end of a 1 h treatment with 1 microgram/ml CNU were fully able to leave these phases but were destined to remain blocked in the following G2M phase (G1 for a minority of them). We also found that cells initially in S phase were slightly delayed in completing their S phase and that 50% of them remained temporarily blocked in the subsequent G2M phase, irrespective of their position in the S phase.

BrdU-Hoechst flow cytometry: a unique tool for quantitative cell cycle analysis

Unlike other techniques, flow cytometric analysis of BrdU-quenched 33258 Hoechst fluorescence may be used to measure cell activation and the G1, S, and G2/M compartment distributions in each of three successive cell cycles after growth stimulation of human peripheral blood lymphocytes. Cell cycle kinetic curves can be constructed from the BrdU-Hoechst flow data which allow the simultaneous assessment of growth fraction, lag-time, compartment exit rate, compartment duration, and compartment arrest. Applications of this new versatile technique include the evaluation of drug and growth factor effects, cell aging, and diagnosis in medicine and immunology.

Effect of 5-fluoro-2'-deoxyuridine (FdUrd) on 5-bromo-2'-deoxyuridine (BrdUrd) incorporation into DNA measured with a monoclonal BrdUrd antibody and by the BrdUrd/Hoechst quenching effect

The purpose of this study was to improve the application of bromodeoxyuridine (BrdUrd) for the flow cytometric analysis of cell kinetics. In order to obtain a quantitative measure of the DNA synthesis rate (or the number of divided cells), BrdUrd should replace thymidine (dThd) completely in the newly synthesized DNA strands. The de novo synthesis of dThd monophosphate competing with BrdUrd incorporation was stopped by fluorodeoxyuridine (FdUrd). Cells of a human leukemic cell line (REH) were exposed to BrdUrd for either 20 min, 8 h, or 24 h. Bromodeoxyuridine incorporation was determined by a monoclonal antibody as well as by the BrdUrd/Hoechst (H) technique. Counterstaining of the DNA was performed with propidium iodide or ethidium bromide. DNA fluorescence was measured in both techniques with a two-parameter flow cytometer, the histograms being analyzed by computer. It was found that FdUrd is required in the BrdUrd/H technique for replacement of dThd at low BrdUrd concentrations and long incubation times. With short incubation periods, as used for detection by the monoclonal anti-BrdUrd antibody, FdUrd increases the incorporated BrdUrd amount when BrdUrd concentrations of 10 microM or less are applied.

Photosensitizing dyes and fluorochromes as substitutes for 33258 Hoechst in the fluorescence-plus-Giemsa (FPG) chromosome technique

Using Allium cepa chromosomes after 5-bromo, 2'-deoxyuridine (BrdU) incorporation, we studied several acid and basic dyes and fluorochromes for their potential as substitutes for 33258 Hoechst in the fluorescence-plus-Giemsa (FPG) technique. All of the dyes and fluorochromes investigated showed a photosensitizing capacity which was slightly lower than 33258 Hoechst in the cases of daunomycin, phloxin, fluorescein, thioflavine T and nuclear fast red, and somewhat higher in the case of eosin Y. Observation and cytophotometric analysis of differentially Giemsa-stained sister chromatids when eosin Y was used as the photosensitizing agent revealed the unsubstituted chromatid to be reddish violet in colour (absorption maximum, 550 nm), while the BrdU-substituted chromatid was blue or pale violet blue (absorption maximum, 580 nm). These results indicate that eosin Y is a useful photosensitizing dye which could be used as a substitute for 33258 Hoechst in the FPG staining technique.

The use of flow cytometry and cell sorting in a human colon carcinoma model

We investigated the growth characteristics of a human colon carcinoma cell line, WiDr, grown in culture flasks and on chick embryonic skin (CES). WiDr cells labeled in vitro with bromodeoxyuridine (BrdU) and analyzed by combined propidium iodide/Hoechst 33258 fluorescence showed evidence of more BrdU incorporation in early S phase as compared to late S phase. When inoculated on the CES, WiDr cells multiplied and invaded the underlying skin. Morphologic examination showed that with extended culture WiDr cells on the CES undergo progressive structural organization with the development of acini and basal lamina, structures similar to those in in vivo tumors. WiDr cells were labeled with monoclonal antibody to carcinoembryonic antigen (CEA) and the brightest 2% of the population was sorted. When subsequently grown on the CES, the sorted cells formed significantly more acinar structures at 3 and 6 days of culture than an unsorted population grown for a comparable time.

Multistation multiparameter flow cytometry: a critical review and rationale

The capacity for fluorescence excitation by beams of different wavelengths at separate points along the sample stream, and the capacity for computer analysis of multiparameter data thus obtained, are now available in flow cytometer/sorter systems from commercial producers. It is now readily apparent to most experienced users of flow cytometers that such multiparameter analysis offers the most convenient solution to the problem of characterizing subpopulations of cells within a mixed population. The use of multiple beams facilitates resolution of fluorescence signals from several probes within or upon a single cell and widens the range of analytical alternatives available to experimenters. This critical review discusses the history of the instrumentation, the parameters now measurable and the probes used for their measurement, and the methods for data analysis. Required sensitivity and precision are discussed, leading to the conclusion that many of the advantages of multistation, multiparameter flow cytometry can be made available in less complex and less costly instruments using less powerful sources and less elaborate computer hardware than are presently incorporated in commercial apparatus.

UV dose-dependent increase in the Hoechst fluorescence intensity of both normal and BrdU-DNA

If the DNA nucleoside thymidine is replaced by bromodeoxyuridine, the fluorescence of the nuclei of Hoechst-stained cells is quenched. The decrease of fluorescence intensity determined by flow cytometry and fluorometry is neutralized independent of the degree of BrdU substitution by an UV-exposure with a dose of 5-10 kJ/m2 to the unfiltered spectrum of a 100 W mercury high-pressure lamp. This dose is equivalent to that obtained in fluorescence microscopy after exposure for about 1 s. We suppose that this approximate matching of the intensities both of normal and BrdU in the DNA resulting in no further quenching. However, the fluorescence intensity of normal Hoechst-stained DNA also is increased by a previous exposure to UV light. We explain the time pattern of the Hoechst fluorescence in the course of an exposure with constant dose rate, by the superimposition of the well-known bleaching by an additional increase of the fluorescence intensity. Our results suggest that the UV-exposure of Hoechst dye creates a brightly fluorescing photoproduct which differs spectroscopically from the original dye. This product is stable in the dark and seems to fluorochrome DNA only if it is formed when the Hoechst dye is bound to DNA, thus increasing the nuclear fluorescence. Phosphorescence was not found.

Flow cytometry and cell proliferation kinetics

Flow cytometric techniques are presented which allow to determine parameters of cell proliferation kinetics by means of histogram sequences after special manipulations of the cell culture under investigation: (a) In the stathmokinetic method metaphase blocking agents are applied which allow the cells of the population to continue progression through interphase and accumulate at 4C DNA content. The development of DNA specific histograms during this process is analysed as to the G1 phase duration and the fraction of nonproliferating cells. (b) In the BUdR/Hoechst method the suppression of Hoechst fluorescence after BUdR incorporation during S phase is taken as a means for inducing a temporal change of histogram shapes without perturbing the cell cycle progression of the population. This temporal development of histogram shapes is analysed as to phase duration, whole cycle time and fraction of nonproliferating cells. (c) By combining the BUdR/Hoechst technique with a simultanous DNA specific stain and analysing with a two-parametrical flow cytometer, more information is obtained from each histogram after BUdR incorporation: The location of cells in the cycle at the beginning of the experiment, the cycle stage at cell harvest, and from this the distance and velocity of progression through the cycle during drug incubation. By introduction of these dynamic methods flow cytometry has become a powerful tool for the study of cell proliferation kinetics in culture.

Flow cytometric analysis of chromosomes and cells using a modified BrdU-Hoechst method

Chromosomes and interphase cells were harvested from cultures of the Chinese hamster line B14 F28 grown in medium containing BrdU up to four cell cycles and stained with the fluorescent dye 33342 Hoechst for flow cytometry. The newly synthetized BrdU-DNA is not stainable by the Hoechst dye which is highly specific for thymidine. The temporal development of the DNA fluorescence after addition of BrdU to the growth medium has been investigated. The chromosomal fluorescence intensity is reduced one step per generation. The extent of the intensity decrease by BrdU incorporation is proportional to the amount of new DNA and it is realized by repeated measurement following an UV-exposure. This UV-illumination stops the quenching by BrdU of the Hoechst stain induced DNA fluorescence. Therefore, the entire DNA content of these chromosomes now becomes measurable. The obtained intensity gain serves as a measure of the extent of the previous BrdU caused intensity shift. In this way we could establish 3 successive mitoses. Principally, this method is suitable also for measurement of whole cells in order to obtain both the number of generations in the experimental period and the phase distribution of the cell cycle.