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

Abstract

Tumour drug-resistant ABCB1 gene expression is regulated at the chromatin level through epigenetic mechanisms. We examined the effects of the histone deacetylase inhibitor trichostatin A (TSA) on ABCB1 gene expression in small cell lung carcinoma (SCLC) drugsensitive (H69WT) or etoposide-resistant (H69VP) cells. We found that TSA induced an increase in ABCB1 expression in drugsensitive cells, but strongly decreased it in drug-resistant cells. These up-and downregulations occurred at the transcriptional level. Protein synthesis inhibition reduced these modulations, but did not completely suppress them. Differential temporal patterns of histone acetylation were observed at the ABCB1 promoter: increase in H4 acetylation in both cell lines, but different H3 acetylation with a progressive increase in H69WT cells but a transient one in H69VP cells. ABCB1 regulations were not related with the methylation status of the promoter À50GC, À110GC, and Inr sites, and did not result in further changes to these methylation profiles. Trichostatin A treatment did not modify MBD1 binding to the ABCB1 promoter and similarly increased PCAF binding in both H69 cell lines. Our results suggest that in H69 drug-resistant SCLC cell line TSA induces downregulation of ABCB1 expression through a transcriptional mechanism, independently of promoter methylation, and MBD1 or PCAF recruitment.

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).…”

“…It appears that, at the levels of the -50 and -100 GC boxes, ABCB1 promoter display an unmethylated profile in 8226 drug-sensitive cells. This promoter hypomethylation in 8226 cells suggest that ABCB1 repression in drug-sensitive cells could be independent of its promoter methylation, a phenomenon previously reported in H69 and SW620 cells (10,17). On the contrary, 8226-Dox40 drug-resistant cell promoter GC boxes were fully methylated.…”

“…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.…”

“…Histone acid extraction and immunoblotting analysis were performed as described previously (10). Antibodies (Upstate Biotechnology, Lake Placid, NY) were used at the following dilutions: antiacetylated histone H3 (1:20000), anti-acetylated histone H4 (1:2000), and peroxidase-conjugated anti-rabbit secondary antibody (1:2000).…”

“…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.…”