Histone methyltransferases regulate the transcriptional expression of ERα and the proliferation of tamoxifen-resistant breast cancer cells

Abstract

Purpose Although tamoxifen remains the frontline treatment for ERα-positive breast cancers, resistance to this drug limits its clinical efficacy. Most tamoxifen-resistant patients retain ERα expression which may support growth and progression of breast cancers. Therefore, we investigated epigenetic regulation of ERα that may provide a rationale for targeting ERα in these patients. Methods Expression levels of the mixed-lineage leukemia (MLL) family of proteins in tamoxifen-resistant breast cancer cells and publicly available breast cancer patient data sets were analyzed. Histone methylation levels in ERα promoter regions were assessed using chromatin immunoprecipitation. Expression levels of ERα and its target gene were analyzed using western blotting and real-time qPCR. Cell-cycle was analyzed by flow cytometry. Results The expression of MLL3 and SET-domain-containing 1A (SET1A) were increased in tamoxifen-resistant breast cancers. An MLL3 chromatin immunoprecipitation-sequencing data analysis and chromatin immunoprecipitation experiments for MLL3 and SET1A suggested that these proteins bound to enhancer or intron regions of the ESR1 gene and regulated histone H3K4 methylation status. Depletion of MLL3 or SET1A downregulated the expression level of ERα and inhibited the growth of tamoxifen-resistant breast cancer cells. Additional treatment with fulvestrant resulted in a synergistic reduction of ERα levels and the growth of the cells. Conclusions The enhanced expression of MLL3 and SET1A in tamoxifen-resistant breast cancer cells supported the ERαdependent growth of these cells by increasing ERα expression. Our results suggest that targeting these histone methyltransferases might provide an attractive strategy to overcome endocrine resistance.

<p>Breast Cancer and Tamoxifen: A Nigerian Perspective to Effective Personalised Therapy</p>

“…A recent report detailed the crucial role of lysine N-methyltransferase 2C (KMT2C/MLL3) and -2F (KMT2F/SET1A) in the regulatory methylation of ERα promoter/enhancer region. 28 This report further confirmed that a knockout of the MLL3 and SET1A genes resulted in a decrease in ERα protein and mRNA level in breast cancer tissues and cell lines. While the epigenetic role of these proteins suggests that they might be useful targets in the development of drugs aimed at reversing decreased hormone-sensitivity in breast tumour, the impact of several mutations and polymorphisms 47 already identified in these genes remain to be elucidated.…”

“…39 While the detailed mechanism underlying tamoxifen resistance is still unclear, the repression of estrogenreceptor-α (ERα, the biotarget of tamoxifen) gene due to epigenetic modification in its promoter region and those of accessory cellular machinery has been reported. 28,[40][41][42] This epigenetic phenotype appears to involve the aberrant methylation of CpG islands (CGIs), deacetylation at N-terminal lysine residue in histones, increased methylation at histone-H3-lysine-4 (H3K4) sites, and altered expression of relevant mRNA levels. 28,43,44 While the complex web of interactions and changes in the activities of coactivators, corepressors, and transcriptional factors involved in the expression and normal physiological functions of ERα is being explored, 39 the intrinsic genomic diversity characteristic of Nigerian populations poses an intriguing perspective.…”

“…28,[40][41][42] This epigenetic phenotype appears to involve the aberrant methylation of CpG islands (CGIs), deacetylation at N-terminal lysine residue in histones, increased methylation at histone-H3-lysine-4 (H3K4) sites, and altered expression of relevant mRNA levels. 28,43,44 While the complex web of interactions and changes in the activities of coactivators, corepressors, and transcriptional factors involved in the expression and normal physiological functions of ERα is being explored, 39 the intrinsic genomic diversity characteristic of Nigerian populations poses an intriguing perspective. Examples are the single nucleotide polymorphisms (SNPs) in DNMT1, the maintenance methylase implicated in the aberrant methylation of CGIs.…”

The MLL3/4 H3K4 methyltransferase complex in establishing an active enhancer landscape

“…Kim et al found that MLL3 could regulate ERα expression through enhancer activation and thereby promote the proliferation of tamoxifen-resistant breast cancer cells. Depletion of MLL3 greatly enhanced the sensitivity of tamoxifen-resistant cells to fulvestrant-based endocrine therapy [ 112 ]. In addition, Gala et al [ 113 ] revealed that depletion of MLL3 causes a significant loss of H3K4me1 and H3K27ac on selected ERα enhancers, as well as downregulation of estrogen-dependent gene expression, which suppresses the proliferation of ER-positive breast cancer cells.…”

Analyzing the impact of CFP1 mutational landscape on epigenetic signaling

“…82 Upregulation of SETD1A increases estrogen receptor α (ERα) expression and activates tamoxifen-resistant breast cancer cells. 83 Similarly, elevated levels of SETD1A are observed in human colorectal cancer cells and patient samples, and are known to activate Wnt target gene expression which ultimately promote tumor growth. 84 Overexpression of a long non-coding RNA, encoded by UCA1 (urothelial cancer associated 1), activates SETD1A methyltransferase activity to deposit H3K4me3 at the promoter regions of TRF2 (telomeric repeat-binding factor 2); leading to its overexpression, nonspecific binding to telomeres and accelerating hepatocytelike stem cells' malignant transformation.…”