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In diseases such as cancer, cells need to degrade the extracellular matrix (ECM) and therefore require high protease levels. Thus, aberrant tissue degradation is associated to matrix metalloproteinases (MMPs) overexpression resulting from different mechanisms including epigenetic events. One of the most characterized epigenetic mechanisms is DNA methylation causing changes in chromatin conformation, thereby decreasing the accessibility to the transcriptional machinery and resulting in a robust gene silencing. Modulation of DNA methylation by DNA hypomethylating agents such as 5-aza-2'-deoxycytidine (5-azadC) is widely used in epigenetic anticancer treatments. Here, we focus on the effects of this drug on the expression level of MMP-1, -2, and -9 in human HT1080 fibrosarcoma cells. We demonstrate that 5-azadC increases MMP expression at both mRNA and protein levels, and promotes invasion potential of HT1080 cells. Using broad-spectrum and specific MMP inhibitors, we establish that MMP-1, but not MMP-2 and -9, plays a key role in 5-azadC-enhanced cell invasion. We show that 5-azadC induces MMP-1 expression through a transcriptional mechanism without affecting MMP-1 promoter methylation status. Finally, we demonstrate that 5-azadC treatment increases the nuclear levels of Sp1 and Sp3 transcription factors, and modulates their recruitment to the MMP-1 promoter, resulting in chromatin remodeling associated to 5-azadC-induced MMP-1 expression. All together, our data indicate that the hypomethylating agent 5-azadC modulates, mainly via Sp1 recruitment, MMP-1 expression resulting in an increased invasive potential of HT1080 cells.

Melanoma is the most severe skin cancer characterized by a bad prognosis at metastatic stages due to resistance to most classical chemotherapies. Invasion of melanoma cells into the surrounding microenvironment locally and at distance of the primary tumour, is facilitated by expression of proteases that degrade the extracellular matrix. Matrix metalloproteinases (MMP) have been long thought as potential therapeutic targets as they are involved in several steps of tumour progression. However, based on this general concept, broad spectrum MMP inhibitors showed weak anticancer potential. Furthermore, MMPs are also expressed by stroma and infiltrating cells. Although, inflammatory conditions lead to uncontrolled expression of MMPs leading to massive matrix destruction, these enzymes are also essential for immune cells to migrate towards the tumour site, and hence mount an anti-tumoral response. During stromal reaction, MMPs also act as non-matrix deteriorating enzymes, and thus modulating the inflammatory response through limited proteolysis of cytokines and chemokines. MMPs contribution to these processes depends on their activity and their expression. Besides the classic control level of transcription by a variety of growth factors and cytokines, the contribution of epigenetic mechanisms on MMPs expression was demonstrated of great importance to extend our knowledge about the role of these enzymes in a specific context such as melanoma progression. Understanding MMPs regulation by epigenetic drugs in melanoma and infiltrated cells will provide a new platform to develop efficient therapies. The therapeutic implication of epigenetic mechanisms to switch a pro-tumoral inflammatory towards an immune anti-tumoral response will be an exciting challenge in which MMPs expression could play a major role.

Aims: Classical biochemical and molecular methods for discerning cells with epigenetic modifications are often biologically perturbing or even destructive. We wondered whether the noninvasive laser tweezer Raman spectroscopy technique allowed the discrimination of single living human cells undergoing epigenetic modifications. Materials & methods: Human Jurkat leukemic cells were treated with inhibitors of histone deacetylases (trichostatin A and MS-275). Epigenetic changes were monitored through histone electrophoresis, nuclear image cytometry and laser tweezer Raman spectroscopy. Results: Treatment of Jurkat cells with histone deacetylase inhibitors increased histone acetylation and induced chromatin organization changes. Characteristic vibrations, issued from laser tweezer Raman spectroscopy analyses, mostly assigned to DNA and proteins allowed discerning histone deacetylase inhibitor-treated cells from control with high confidence. Statistical processing of laser tweezer Raman spectroscopy data led to the definition of specific biomolecular fingerprints of each cell group. Conclusion: This original study shows that laser tweezer Raman spectroscopy is a label-free rapid tool to identify living cells that underwent epigenetic changes.

ABCB1 gene overexpression has been described as an important mechanism for resistance to conventional chemotherapy in multiple myelomas. In the refractory multiple myelomas, other drug regimens have been successfully applied, including thalidomide treatments. Besides its well-documented anti-angiogenic effects, thalidomide therapy could result in a decrease in ABCB1 gene expression. In this study, we analysed the effects of a 24-h short-term treatment by thalidomide or its active metabolite phthaloyl glutamic acid (PGA) on nuclear chromatin higher-order organisation and ABCB1 gene expression in drug-sensitive and drug-resistant 8226 human myeloma cells. As compared to sensitive cells, 8226-Dox40 drug-resistant cells exhibited an increase in chromatin texture condensation and ABCB1 gene over-expression. At this gene promoter level, the -50 and -100 GC boxes displayed an unmethylated profile in drug-sensitive cells whereas drug-resistant cell promoter GC boxes were fully methylated. Thalidomide and PGA induced significant chromatin textural changes in 8226-Dox40 drug-resistant cells only with neither alteration in ABCB1 gene expression nor methylation profile of its promoter. Conversely thalidomide and PGA induced down-regulation of VEGF gene expression in both drug-sensitive and -resistant myeloma cells. These data suggest that short-term treatments by thalidomide or PGA do not induce any significant change on ABCB1 gene expression though they modulate chromatin supra-organisation in drug-resistant 8226 human myeloma cells.

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.