ABSTRACT2-Methoxyestradiol (2ME), an endogenous metabolite of 17β-estradiol, has been reported to play an active role in the induction of apoptosis in both proliferating endothelial and cancer cells. Since it has been indicated that an increased ratio of pro-apoptotic Bax protein to anti-apoptotic Bcl-2 protein expression can be associated with apoptosis, and since the exact action mechanism of 2ME is still not clearly defined and appears to vary according to cell type, the influence of 1 μM 2ME was investigated on Bax and Bcl-2 expression levels in squamous esophageal carcinoma cells. 2ME exposure led to statistically significant decreases (0.69 over DMSO controls) in Bcl-2 expression levels. In contrast, no statistically significant effects were observed on Bax expression levels after exposure to 2ME. The Bax/Bcl-2 ratio for 2ME-exposed cells was 1.45, normalised against Bcl-2 levels. Although the exact mechanisms of apoptosis induction in squamous esophageal cancer cells require further investigation, the present study suggests that this altered ratio in favor of Bax could lead to the induction of apoptosis in these cells.2-Methoxyestradiol (2ME), once considered an inactive end-metabolite of 17β-estradiol, has been reported to contain antiproliferative effects on various tumor cell lines regardless of the cell's hormone receptor status (10). Early research on 2ME's biological activity stated its effect on mitotic spindles and cell cycle progression. 2ME caused mitotic accumulation and abnormal mitotic spindle formation in both estrogen receptor (ER) positive-and ER negative cells (12). Furthermore, 2ME targeted proliferating endothelial cells as well as tumor cells, culminating into the initiation of apoptosis. As a consequence, this endogenous estradiol metabolite has emerged as a promising anticancer agent (9).New evidence with regard to 2ME's action mechanism implicates the involvement of both the extrinsic and intrinsic pathways of apoptosis induction. However, the exact mechanism of 2ME is still not clearly defined and appears to vary according to cell type (11). In addition, we have previously shown that degree of differentiation of esophageal carcinoma cells influences the susceptibility of tumor cells to the anti-mitogenic effects of prostaglandinA 2 , another endogenous metabolite playing an active role in the induction of apoptosis. More pronounced effects were observed in less differentiated squamous esophageal cancer cell lines, while more differentiated and normal cells appeared to be less affected (5).Dose-dependent studies revealed that 10 −6 M 2ME was most inhibitory to WHCO3 cell proliferation and decreased cell numbers by almost 60% (13). Light microscopy as well as electron microscopy demonstrated hallmarks of apoptosis in WHCO3 cells. These hallmarks included cell shrinkage,
The effects of 20 μg/mL exogenous prostaglandin A 2 (PGA 2 ) were determined on Bax, Bcl-2 and proliferating cell nuclear antigen (PCNA) expression levels in MCF-7 cells. Flow cytometric analysis indicated a pronounced increase in the S phase and a decrease in the G 1 phase, whereas a significant increase in the DNA content preceding the G 0 /G 1 peak was also observed after 48 h of exposure to PGA 2 . Confirmation of apoptosis was determined after 12 h, 36 h and 48 h of PGA 2 exposure employing the mitosensor reagent that detects potential changes in the mitochondrial membrane. Twenty-eight percent of PGA 2 -exposed cells were in apoptosis when compared to the 7.1% vehicle-treated cells after 48 h. PGA 2 exposure led to statistically significant increase (1.25-fold) over vehicle-treated controls in Bax expression levels. Decreases in Bcl-2 (0.79-fold), as well as PCNA (0.69-fold) expression levels over vehicle-treated controls were observed. The Bax/Bcl-2 ratio for PGA 2 -exposed cells was 2.7. The present study suggests that an accumulation in the S phase, a decrease in expression levels of PCNA, as well as an altered ratio in favor of Bax, could lead to the induction of apoptosis in these cells.Research has shown that prostaglandin A 2 (PGA 2 ), a cyclopentenone and endogenous metabolite derived from arachidonic acid, exhibits potent anti-proliferative activity in vivo (5,14,20,22) and in vitro (1, 17-19, 21, 23). Concentration-dependent studies from previous research (12) revealed that 20 μg/mL results in optimal growth inhibition in vitro. This was confirmed in our laboratory where IC 50 = 20 μg/ mL was determined (results not shown). PGA 2 inhibited proliferation of tumor cells depending on dose, duration of exposure and cell type (12). In addition, we have demonstrated that the breast adenocarcinoma cells, MCF-7, were more susceptible to the anti-mitogenic effects of PGA 2 when compared to human epithelial cervix carcinoma (HeLa) cells (11). Furthermore, degree of differentiation of oesophageal carcinoma cells was also shown to influence tumor cell susceptibility to the anti-mitogenic effects of PGA 2 . More differentiated and normal cells appeared to be less affected, while more pronounced effects were observed in less differentiated cell lines (12).Since PGA 2 targets active proliferating cells and plays an active role in the induction of apoptosis, especially in cells that present with carcinogenic properties (12,25), the aim of this study was to confirm the anti-mitogenic effects of PGA 2 and to investigate the influence of PGA 2 on Bax, Bcl-2 and PCNA expression in MCF-7 cells in order to suggest a possible mechanism for induction of apoptosis.
This study describes the isolation of a 11 kDa paralysis toxin from crude larval extracts of Argas (Persicargas) walkerae by exploiting the cross-reactivity of a monoclonal antibody (4B12), directed against the paralysis toxin of Rhipicephalus evertsi evertsi. This low molecular mass is in contrast to previous findings of a 60-70 kDa toxin for A. (P.) walkerae, but is similar to neurotoxins isolated from venomous forms of the class Arachnida, which comprise the orders Araneae (spiders). Scorpionida (Scorpions) and Acari (ticks and mites). Since numerous antigenic bands, ranging between 11 and 115 kDa, were detected by the monoclonal antibody 4B12, the possibility of toxin-complex formation and the effect of pH on the latter were investigated by means of HPLC and ammonium sulphate precipitation. The results suggest that physiological conditions, with respect to pH and ionic strength, promote the formation of heterogeneous toxin-complexes while an acidic pH favours the formation of a more homogeneous toxin-containing complex. Furthermore, the effect of partially purified toxin on neurotransmitter release from crude rat brain synaptosomes was investigated, since tick paralysis toxins are hypothesised to inhibit neurotransmitter release from the presynaptic terminal. Both calcium-dependent, as well as calcium-independent release was inhibited by the toxin-containing sample.
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