Apoptotic pathways depend on the target enzymatic activity and not on the triggering agent

Multiple roles of matrix metalloproteinases during apoptosis

Structural, molecular and biochemical approaches have contributed to piecing together the puzzle of how matrix metalloproteinases (MMPs) work and contribute to various disease processes. However, MMPs have many unexpected substrates other than components of the extracellular matrix which profoundly influence cell behaviour, survival and death. With the current understanding of diverse/novel roles of matrix metalloproteinases--particularly their direct or indirect relevance for the early steps during programmed cell death--some seemingly contrasting results seem less surprising. To better target MMPs an appreciation of their many extracellular, intracellular and intranuclear functions, often acting in opposing directions with paradoxical roles in cell death, is carefully required.

Using CTLL-2 and CTLL-2 bcl2 cells to avoid interference by apoptosis in the in vitro micronucleus test

In vitro assays for chromosome aberrations (i.e., in vitro micronucleus and in vitro metaphase analysis tests) frequently produce false-positive or exaggerated-positive results. Our previous work suggested that apoptosis interferes with these tests, producing misleading results. These previous studies were conducted by performing the in vitro micronucleus test in CTLL-2 cells and a CTLL-2 cell derivative stably transfected with the apoptosis inhibitor gene bcl2. In the present study, these previous observations were extended by examining micronucleus induction with a larger number of compounds in both CTLL-2 and CTLL-2 bcl2 cells and measuring apoptosis with annexin V-FITC. Both cell lines were treated with different classes of compounds that were anticipated to be exclusively apoptosis inducers, or compounds known to be clastogens or aneugens, some of which were anticipated to be both genotoxic and apoptotic. We were able to confirm that compounds that are only apoptogenic induced micronuclei in CTLL-2 but not CTLL-2 bcl2 cells, indicating that the positive responses are due to apoptosis in CTLL-2 cells. Some genotoxins (clastogens and aneugens) did not produce apoptosis by the annexin V assay and gave similar responses in CTLL-2 and CTLL-2 bcl2 cells. Finally, higher responses were induced in CTLL-2 cells compared to CTLL-2 bcl2 cells that were treated with aneugens or clastogens that were also apoptosis inducers, suggesting that the greater response in CTLL-2 cells is a consequence of both genotoxicity and apoptosis. Finally, it was demonstrated that just eliminating CTLL-2 cells having three or more micronuclei from scoring was not adequate for correctly evaluating agents that only produce apoptosis. The results indicate that coupling the in vitro micronucleus test in both CTLL-2 and CTLL-2 bcl2 cells with the measurement of apoptosis is able to distinguish the genotoxic effects of a test compound from its apoptotic potential and is able to avoid interference from apoptosis in the in vitro micronucleus test. These observations may provide the basis for a useful genotoxicity assay.