Nuclear chromatin texture and sensitivity to DNase I in human leukaemic CEM cells incubated with nanomolar okadaic acid

Abstract

It is now known that the analysis of chromatin texture can be used in oncology as a sensitive detection method, either to define diagnostic classifications or to locate a lesion along a defined trend curve. However, the functional significance of these variations in textural features remains sometimes unclear. Several drugs have been shown to be able to modulate chromatin structure. Among them, the phosphatase inhibitor okadaic acid at low concentration can increase accessibility to DNA in chromatin of carcinoma cells. This paper demonstrates that short exposures (0-3 h) to a 10-nM dose of okadaic acid induced an increased sensitivity to DNase I digestion in human CEM leukaemic cell nuclei and that this sensitization was associated to variations of nuclear texture characteristics, as evaluated by image cytometry. CEM cells treated with okadaic acid for 0-3h displayed changes in chromatin supraorganization with a more homogeneous and fine chromatin texture, as compared to control cells. This suggests that the appearance of an open configuration of chromatin structure as evaluated by biochemical methods corresponds to a more decondensed texture of nuclei measured by image cytometry. Longer exposures (6-24h) of CEM cells to 10 nM okadaic acid lead to apoptosis. As reported previously for camptothecin-treated HL60 cells, okadaic acid-treated CEM cells display biphasic nuclear chromatin texture changes, i.e. a decondensation phase followed by the appearance of typical apoptotic cells with a smaller nuclear area and a highly condensed chromatin. Finally, using the multidrug-resistant CEM-VLB cell line, it was confirmed that these multidrug-resistant cells also display cross-resistance to okadaic acid, as this compound was unable to induce either increased DNase I sensitivity, apoptosis, or altered nuclear texture in this particular cell line.

Constitutive expression of ectopic c-Myc delays glucocorticoid-evoked apoptosis of human leukemic CEM-C7 cells

“…To rule out this possibility, we tested the ability of C7-MycER TM cells to respond to agents that have been previously demonstrated to cause apoptotic death of CEM cells. Figure 2c shows that both parental CEM-C7-14 cells and C7-MycER TM cells respond similarly to staurosporine and okadaic acid, agents that are known to evoke apoptotic responses in CEM cells via mechanisms that are distinct from each other and from GC-evoked apoptosis (Bruno et al, 1992;Kiguchi et al, 1994;Yatouji et al, 2000;Yerly-Motta et al, 1999), and are not known to involve c-Myc. These results con®rm our hypothesis that protection from Dex-evoked apoptosis is caused speci®cally by constitutive c-Myc expression rather than via selection for a survival phenotype due to expression of antiapoptotic gene(s).…”

Effects of the histone deacetylase inhibitor trichostatin A on nuclear texture and c‐jun gene expression in drug‐sensitive and drug‐resistant human H69 lung carcinoma cells

“…However, identification of the biological events at the origin of the variations in textural features is sometimes difficult. We previously reported that direct modifications in chromatin structure by okadaic acid induced significant changes in nuclear texture (12). These changes could be of utmost importance because it is obvious that higher‐order chromatin structure plays a major role in gene regulation, whereby actively transcribed genes are mostly characterized by an open chromatin configuration.…”

Nuclear chromatin patterns in 3 glucocorticoid-resistant RPMI 8226 human myeloma cell sub-lines: Correlations with cell growth and immunological phenotype

“…14,15,51 Whether GC-resistant cells display an active SWI/SNF remodeling complex remains to be further elucidated but appears rather likely as (1) CD44 expression is under the control of AP-1 which needs a functional SWI/SNF complex for its transactivating activity, 52 and (2) this complex seems to play a role in the nuclear size maintenance, the presence of mutant remodeling enzyme resulting in nuclear size increase. 53 In conclusion, analysis of nuclear texture detects specific chromatin patterns and distribution in glucocorticoid-resistant RPMI 8226 cell sub-lines.…”