Article

The Bcl-2 protein family.

Serono Pharmaceutical Research Institute, 14 chemin des Aulx, Plan-les-Ouates/Geneva, CH-1228, Switzerland.
Experimental Cell Research (Impact Factor: 3.37). 05/2000; 256(1):50-7. DOI: 10.1006/excr.2000.4839
Source: PubMed
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    ABSTRACT: Expression of the anti-apoptotic proteins Bcl-2 and/or Bcl-xL is greatly elevated in many advanced cancers, especially those resistant to standard therapies, such as radiation or chemotherapy. It has been suggested that those two proteins would be attractive targets for the development of new cancer treatments. Photodynamic therapy (PDT) with photosensitizers that localize in or target mitochondria, such as the phthalocyanine Pc 4, specifically attack the anti-apoptotic protein Bcl-2, generating a variety of oxidized, complexed, and cleaved photoproducts. The closely related protein Bcl-xL is also a target of Pc 4-PDT. In a recent study employing transient transfection of an expression vector encoding deletion mutants of Bcl-2, we identified the membrane anchorage regions of the protein that are required to form the photosensitive target. In spite of the demonstrated photodamage to Bcl-2 (and Bcl-xL), how the photodamage translates into changes in the sensitivity of cells to PDT-induced apoptosis or other modes of cell death is not clear, and it also remains unclear how elevated amounts of anti-apoptotic proteins in tumors might make them more or less responsive to PDT. In the present study, we have studied the PDT response of MCF7 human breast cancer cells overexpressing wild-type Bcl-2 or certain deletion mutants either in a transient or stable mode. We show that cells expressing modestly elevated amounts (<10-fold increase) of Bcl-2 and in which the pro-apoptotic protein Bax is not upregulated do not differ from the parental cells with respect to PDT-induced cell killing. In contrast, cells expressing higher amounts (>50-fold increase) of Bcl-2 or certain mutants are made significantly more resistant to the induction of apoptosis and the loss of clonogenicity upon exposure to Pc 4-PDT. In the presence of high levels of Bcl-2, extensive photodamage requires higher PDT doses. We conclude that Pc 4-PDT targets Bcl-2 and Bcl-xL, eliminating one mechanism that protects the tumor cells from other types of therapy. However, it is possible that cells expressing very high levels of the anti-apoptotic proteins might still be resistant to PDT. The data suggest that PDT with a non-vascular-targeting photosensitizer might be effective in a combination treatment in which Bcl-2 and Bcl-xL are first photodamaged before delivery of a second agent.
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    ABSTRACT: Background The important role of WT1 in early folliculogenesis was evident from its restricted expression pattern in immature follicles and from its involvement in transcriptional control of inhibin-¿ and FSH receptor. There is also considerable evidence that WT1 is a potent inhibitor of apoptotic cell death in the developing kidney and male germ cells, suggesting that it could play a role in the regulation of follicle survival. Therefore, we evaluated if WT1 involves in cell survival of granulosa cells (GCs) during the FSH-independent stage.MethodsGCs were obtained from small preantral follicles of immature rat ovary. Bax and bcl-2 mRNA and protein levels in GCs transfected with WT1 (¿KTS) or WT1 (+KTS) were analyzed by Real-time RT-PCR and immune-blotting analysis. Cell viability was measured with MTT assays and apoptosis was analyzed with caspase 3/7 activity and TUNEL assay. The mechanism by which WT1 regulates Bax expression was investigated using Bax promoter-luciferase reporter assay and ChIP assays from GCs.ResultsHere, we showed that WT1 (¿KTS) suppressed endogenous Bax transcript and protein expression, and this inhibition resulted from direct binding of WT1 in the Bax promoter region in vivo. In addition, anti-apoptotic effects of WT1 (¿KTS) were demonstrated based on MTT assays, a sensitive bioluminescence caspase 3/7 assay and TUNEL assays. On the other hand, WT1 has no role on bcl-2 expression in GCs.Conclusion These findings suggest that activation of WT1 is necessary for maintenance of GC survival during early stage of follicles and WT1 can play a role in protecting apoptosis through the regulation of upstream activator (Bax), as well as through regulation of downstream effecter (caspases 3 and 7).
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