Interphase and M-phase oral KB carcinoma cells are targetted in staurosporine-induced apoptosis

Photochemical Synthesis of Indolocarbazoles through Tandem Indolization/Dimerization/Mannich Cyclization from Allenes

Indolocarbazole alkaloids and their derivatives were discovered to have potent protein kinase and topoisomerase I inhibitory activities. Disclosed herein is the photochemical synthesis of the indolocarbazole ring system from N-allenyl-2-iodoanilines. The tandem protocol included visible-light-mediated 5-exo-trig radical cyclization and subsequent radical dimerization, followed by acid-promoted deprotection and intramolecular Mannich cyclization. This strategy showed exceptional functional group tolerance and was successfully applied in the concise synthesis of natural products tjipanazoles B and D.

Staurosporine induces apoptosis in human papillomavirus positive oral cancer cells at G2/M phase by disrupting mitochondrial membrane potential and modulation of cell cytoskeleton

Our study demonstrates that staurosporine (STS), a protein kinase inhibitor from Streptomyces sp., induces apoptosis in human papillomavirus positive oral carcinoma cells (KB) in a dose dependent manner. Growth inhibition studies revealed an IC(50) value of approximately 100 nM. STS induced marked nuclear fragmentation and inter-nucleosomal cleavage compared to untreated cells. It also caused dose dependent disruption of mitochondrial membrane potential and activation of caspase-3, indicating involvement of mitochondria-mediated cell death signaling in KB cell apoptosis. We found time-dependent arrest of the KB cells at G2/M phase of cell cycle. Using fluorescence microscopy, we have further shown that STS treatment disrupts microtubules and reorganizes F-actin after 6h exposure. Taken together, our results suggest that STS induces mitochondria-mediated KB cell apoptosis at G2/M phase by altering cell cytoskeletal network.

Effect of sulphur mustard on human skin cell lines with differential agent sensitivity

The ability of sulphur mustard (HD) to induce DNA damage places limits on the efficacy of approaches aimed at protecting human cells from the cytotoxic effects of HD using a variety of protective agents such as thiol-containing esters and protease inhibitors. In the present study, potential alternative strategies were investigated by examining the differential effects of HD on G361, SVK14, HaCaT and NCTC 2544 human skin cells. The G361 cell line was more resistant to the cytotoxic effects of HD than the NCTC, HaCaT and SVK14 cell lines at HD doses of >3 and <100 microM HD as determined by the MTT assay. At 72 h after exposure to 60 microM HD there was up to an 8.8-fold difference (P < 0.0001) between G361 and SVK14 cell culture viability. Buthionine sulphoximine (BSO) pretreatment increased the sensitivity of all four cell lines to HD. A substantial proportion of the resistance of G361 cells to HD was attributable to BSO-mediated effects on antioxidant-mediated metabolism, although G361 cultures still retained a high degree of viability at 30 microM HD following BSO pretreatment. Cell cycle analysis confirmed that SVK14 cells were relatively more sensitive to HD, as shown by the 2.1-fold reduction (P < 0.0001) in the percentage of cells in G0/G1 phase 24 h after HD exposure compared with control cultures. This compared well with a 1.2-fold increase (P < 0.05) in the percentage of G361 cells in G0/G1 phase following HD exposure, suggesting the existence of a more efficient G0/G1 checkpoint control mechanism in this cell line. Manipulation of the cell cycle using various modulating agents did not increase the resistance of cell lines to the cytotoxic effects of HD.

Inducing the cell cycle arrest and apoptosis of oral KB carcinoma cells by hydroxychavicol: roles of glutathione and reactive oxygen species

Hydroxychavicol (HC; 10 - 50 microM), a betel leaf component, was found to suppress the 2% H(2)O(2)-induced lucigenin chemiluminescence for 53 - 75%. HC (0.02 - 2 microM) was also able to trap superoxide radicals generated by a xanthine/xanthine oxidase system with 38 - 94% of inhibition. Hydroxyl radicals-induced PUC18 plasmid DNA breaks was prevented by HC (1.6 - 16 microM). A 24-h exposure of KB cells to HC (0.5, 1 mM) resulted in 54 - 74% cell death as analysed by a 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide (MTT) assay. HC (10, 50 microM) further suppressed the growth of KB cells (15 and 76%, respectively). Long-term colony formation of KB cells was inhibited by 51% with 10 microM HC. Pretreatment of KB cells with 100 microM HC inhibited the attachment of KB cells to type I collagen and fibronectin by 59 and 29%, respectively. Exposure of KB cells to 0.1 mM HC for 24 h resulted in cell cycle arrest at late S and G2/M phase. Increasing the HC concentration to 0.25 and 0.5 mM led to apoptosis as revealed by detection of sub-G(0)/G(1) peaks with a concomitant decrease in the number of cells residing in late S and G(2)/M phase. Inducing the apoptosis of KB cells by HC was accompanied by marked depletion in reduced form of GSH (>0.2 mM) and the increasing of reactive oxygen species production (>0.1 mM) as analysed by CMF- and DCF-single cell fluorescence flow cytometry. These results indicate that HC exerts antioxidant property at low concentration. HC also inhibits the growth, adhesion and cell cycle progression of KB cells, whereas its induction of KB cell apoptosis (HC>0.1 mM) was accompanied by cellular redox changes.

Fas-mediated apoptosis of proliferating, transiently growth-arrested, and senescent normal human fibroblasts

Previous studies suggest that apoptotic signaling may require proteins that are critical to cellular proliferation and cell cycle regulation. To further examine this question, proliferating, transiently growth-arrested, and senescent normal human fibroblasts were induced to undergo apoptosis in response to two distinct mediators of apoptosis-Fas (APO-1/CD95) death receptor and staurosporine. Ligation of the Fas receptor in the presence of cycloheximide or actinomycin D resulted in apoptosis of proliferating cells, cells transiently growth arrested by gamma-irradiation or serum starvation (i.e., G(0) arrest), and permanently growth-arrested senescent fibroblasts. Proliferating and G(0)-arrested cells were also susceptible to staurosporine-mediated apoptosis. Surprisingly, gamma-irradiated cells did not undergo staurosporine-mediated apoptosis, and remained viable for a prolonged time. Fas-mediated apoptosis of senescent fibroblasts was evidenced by chromosome condensation and by activation of caspase-8 and -3, proteases crucial for the execution of the Fas apoptosis pathway. In addition, ligation of the Fas receptor in G(0)-arrested cells did not result in the activation of p34(cdc2) kinase, arguing that activation of this kinase is not essential in this apoptotic process. From these studies we conclude that proliferating, transiently growth-arrested, and senescent normal human fibroblasts are susceptible to apoptotic signals and that apoptosis is not necessarily dependent upon cell cycle or proliferative state of the cell.

Metallothionein expression and nuclear size in benign, borderline, and malignant serous ovarian tumours

Metallothioneins (MTs) are low-molecular-weight proteins involved in metalloregulatory functions such as cell proliferation, growth, and differentiation. In recent years, MT expression has been linked with carcinogenesis, resistance to cancer therapy, and tumour progression. However, the significance of MT expression in ovarian cancers is at present inadequately documented. In this study, MT immunohistochemistry was performed in 12 benign, 14 borderline, and eight malignant serous tumours of the ovary. The intensity of the immunostaining was evaluated by image analysis. There was a significantly higher number of MT-immunopositive cells in the multilayered epithelial cells of borderline serous tumours (atypical proliferative serous tumours) than in the single layered epithelial cells within the same tumour, and in the single cell layer of benign serous tumours. There was no difference in the expression of MTs in the single layered tumour cells of benign and borderline serous tumours. Significantly higher numbers of MT-immunopositive cells were observed in both the single and the multilayered epithelial cells of serous carcinomas, the highest number being observed in the multiple layers of serous carcinomas. The positively stained malignant tumour cells in both single and multiple layers were larger than the negatively stained cells in benign, borderline, and malignant serous ovarian tumours. There was moderate to intense staining. These findings indicate that there is increased expression of MTs in the progression of malignancy, which could be used as a marker in grading the three groups of ovarian serous tumours and for determining prognosis.

Screening of five specific cell cycle inhibitors using a T cell lymphoma cell line synchrony/release assay

To obtain different cell populations at specific cell cycle stages, we used a cell culture synchronization protocol. Effects of five different cell cycle inhibitors acting throughout the cell cycle were examined by DNA flow cytometric analysis of a synchrony/release lymphoma cell line (CEM). The screening synchronized protocol showed that staurosporine, mimosine and aphidicolin are reversible G1 phase inhibitors that act at different times. Staurosporine acted in early G1, exhibited the strongest cytotoxic effect, and induced apoptosis. Mimosine and aphidicolin acted in late G1 and at the G1/S boundary, respectively. Hydroxyurea arrested CEM cells in early S phase, but later than the aphidicolin arrest point. Nocodazole synchronized CEM cells in M phase. All the inhibitors examined in this study can be used to synchronize cells at different phases of the cell cycle and were reversible with little toxicity except for staurosporine which is highly toxic. Because the regulatory mechanism of the cell cycle is disrupted by their effects on protein synthesis, however, these drugs must be used with caution.

Lineage-related susceptibility of human hemopoietic cell lines to apoptosis

Apoptosis plays a fundamental role in shaping normal hematopoiesis. We have investigated the relationship existing between susceptibility to apoptosis and lineage commitment in hemopoietic cells. The presence and degree of apoptosis were investigated in myeloid (HL-60 and K562), T (Jurkat and MOLT-4), and B (CESS and Raji) lymphoid cell lines by using a variety of techniques-transmission electron and light microscopy, flow cytometry and DNA gel electrophoresis. The major achievement of this study is that hematopoietic cells respond to different chemical (staurosporin, tiazofurin, camptothecin) and physical (hyperthermia or hypothermia) stimuli by apoptosis in a lineage-related way. Moreover, with respect to the methods used to detect apoptosis, a strong correlation was observed between the presence of the hypodiploid peak determined by flow cytometry and the DNA laddering evaluated by gel electrophoresis, but both techniques failed to demonstrate the presence of apoptosis in some cases. We conclude that cells of different hematopoietic lineages mostly show a lineage-related behaviour in their apoptotic response to different stimuli, suggesting that the lineage commitment and the stage of differentiation can confer different sensitivities to specific apoptotic stimuli. Moreover, morphological techniques still represent the most reliable approach to detect apoptosis in hemopoietic cells.

Alteration of proto-oncogenes during apoptosis in the oral squamous cell carcinoma cell line, SAS, induced by staurosporine

Staurosporine (ST) has been reported to induce apoptosis in many kinds of cultured cells. The pathway of the apoptosis induced by ST is still not clear. Certain proto-oncogene expressions have been shown to be involved in the apoptotic pathway. The present study characterized apoptosis induced by ST in the oral squamous cell carcinoma cell line, SAS, focusing on the alteration of proto-oncogene expression. SAS showed typical apoptotic features upon exposure to ST. We compared the level of gene expression in apoptosis induced by ST with that by withdrawal of serum, which is a common system to induce apoptosis. By RT-PCR analysis, ST-induced apoptosis showed c-fos and c-jun up-regulation, whereas serum withdrawal-induced apoptosis showed c-jun up-regulation and the same levels of p21/waf-1 and c-myc. These results indicate that ST can rapidly induce apoptosis in SAS, possibly via a c-fos and c-jun pathway.

Apoptotic condensations in M-phase cells

BACKGROUND

Apoptosis is a morphologically distinctive form of programmed cell death/cell suicide in which genomic DNA degradation/fragmentation and variegated dense chromatin aggregates are characteristic hallmarks that have never been demonstrated in mitotic cells. Perceptions of mutual exclusivity between apoptosis and mitosis imply that M-phase cells cannot be apoptotic. However, in the present study we show apoptotic morphologies in M-phase cells after an acute oxidative stress and endonuclease digestion.

METHODS

Degradation of genomic DNA in human Chang liver cells (American Type Culture Collection, ATCC CCL13) was demonstrated by flow cytometric cell-by-cell evaluation of (a) propidium iodide intercalative binding to DNA and (b) terminal deoxynucleotidyl transferase (TdT)-mediated 3'OH nick end labeling (TUNEL) of fragmented DNA. Oxidative stress was imposed by a 30-min prepulse with 200 microM vanadyl(4), which produces hydroxyl free radicals (OH*), the most reactive of the free radical species. Oxidative stress in the cells was demonstrated by evaluating glutathione-S-transferase (GST)-mediated monochlorobimane-glutathione adduct fluorescence for glutathione content, the main reducing agent of a cell, and methylene blue redox metachromasia, which is a deep color when oxidized and colorless when reduced. Cells with DNA fragmentation were highlighted by TUNEL. Apoptotic morphologies were visualized by staining with Giemsa and neutral red dyes and by DNA-propidium iodide binding to chromatin. Direct endonuclease induction of apoptotic morphologies in permeabilized M-phase cells was produced by 1 hr incubation (37 degrees C) with 16 units/ml of micrococcal nuclease.

RESULTS

The genomic DNA of proliferative cells, namely in G2/M phase of the cell cycle, was degraded by vanadyl(4) prepulsing and by micrococcal nuclease digestion, concomitantly with DNA fragmentation shown by TUNEL. Cytological profiles showed GSH depletion and M-phase cells with particularly high oxidative reactivity indicated by methylene blue redox metachromasia. DNA fragmentation in M-phase cells was highlighted by TUNEL. Characteristic apoptotic condensations, ranging from single-ball condensations to "pulverized" aggregates of a mitotic catastrophe, buddings, and "apoptotic bodies," were found in prophase, metaphase, anaphase, and telophase mitotic cells. The observed separation of condensed chromatin aggregates from the main chromosome mass in prophase and metaphase cells could explain micronuclei, linking it with apoptosis. Direct endonuclease digestion readily produced apoptotic morphologies in interphase and in M-phase cells.

CONCLUSION

Apoptotic morphologies in M-phase cells can be induced indirectly via oxidative stress or directly via endonuclease activity, which has long been established as a pervading hallmark of apoptosis.