Differential modulation of nuclear texture, histone acetylation, and MDR1 gene expression in human drug-sensitive and -resistant OV1 cell lines

Abstract

Abstract. Image cytometric study of pathological specimens or cell lines has suggested that epigenetic mechanisms are likely to play a major role in determining chromatin patterns evaluable through nuclear texture analysis. We previously reported that nuclear textural changes observed in the OV1-VCR etoposide-resistant ovarian carcinoma cell line were associated with an increased acetylated histone H4 level. In this study we analyzed the effects of treatments with the HDAC inhibitor trichostatin A (TSA) or with nickel subsulfide on histone H4 acetylation, nuclear texture, and MDR1 gene expression in drug-sensitive IGROV1 and drug-resistant OV1-VCR cell lines. In IGROV1 cells, TSA induced an increase in acetylated H4 level associated with a chromatin textural decondensation and an increase in MDR1 gene expression. In OV1-VCR cells, a similar increase in H4 acetylation was observed, but nuclear texture or MDR1 gene expression remained unchanged. ChIP analysis revealed that MDR1 gene expression remained stable in TSA-treated OV1-VCR cells despite a localized increase in H4 acetylation at the promoter level. Analysis of the methylation status of MDR1 promoter showed an increase in DNA methylation at 3 specific sites in OV1-VCR cells, that could participate to TSA low responsiveness in these cells. Treatment with nickel subsulfide induced a decrease in H4 acetylation without any effect on nuclear texture characteristics in both cell lines. In OV1-VCR cells, nickel subsulfide induced a significant down-regulation of the MDR1 gene expression. These results indicate that modulation of histone H4 acetylation level can be associated with up-or down-regulation of the MDR1 gene in OV1 cells. However, this modulation does not always result in chromatin pattern alterations and these data emphasize the complexity of chromatin texture regulation in tumor cells.

Thalidomide alters nuclear architecture without ABCB1 gene modulation in drug-resistant myeloma cells

“…Considerable experimental evidence suggests that histone acetylation and DNA methylation are involved in this control (16)(17)(18)(19). Consistent with these and other previous studies we also observed that treatments which modulate nuclear architecture could result in ABCB1 up-or down-regulations in various tumour cell lines (3,10,11).…”

“…In this context, we reported previously that histone deacetylases inhibitor TSA could induce chromatin texture changes in tumour cell lines (H69, OV1) and that this effect could, in some cases, be associated with ABCB1 gene expression regulations (10,11). Previous studies indicate that thalidomide could also play a role on drug-resistance.…”

“…The cell spots were air-dried and fixed in alcohol-formalin mixture (95% ethanol, 3% formaldehyde in saline: 3:1) for 10 min. After acid hydrolysis with 5 M HCl for 30 min, they were stained by the Feulgen method as previously described (11). Image cytometry was performed with an image analysis system (SAMBA 2005, Samba Technologies, Meylan, France) coupled to a color 3CCD camera (XC-007P, Sony Corp., Japan) and a microscope (Axioscop, Karl Zeiss, Oberkochen, Germany).…”

“…The mechanisms underlying this decrease remain unclear but could include some epigenetic control of the ABCB1 gene expression. We showed previously that inhibition of histone deacetylases led to ABCB1 gene modulation, both in drug-sensitive and -resistant cells, a phenomenon associated with chromatin structure modifications (3,10,11). Considerable efforts have been made recently towards the definition of the regulatory mechanisms that control the expression of ABCB1 gene in tumour cells (reviewed in ref.…”

The histone deacetylase inhibitor trichostatin A downregulates human MDR1 (ABCB1) gene expression by a transcription-dependent mechanism in a drug-resistant small cell lung carcinoma cell line model

“…However, ABCB1 promoter of H69VP cells is constitutively strongly hypomethylated, and the downregulation of ABCB1 expression by HDAC inhibition could require such low level of DNA methylation in ABCB1 promoter. Indeed, we have previously shown that ABCB1 expression remains unchanged after TSA treatment of the multidrug-resistant human ovarian adenocarcinoma cell line OV1/VCR, in which ABCB1 promoter is slightly hypermethylated compared to its sensitive IGROV1 counterpart (Yatouji et al, 2007). Further methylation analysis on different cell lines and clinical samples is required to clarify the relevancy of basal methylation status of ABCB1 promoter on ABCB1 repression by HDAC inhibitors.…”