Direct measurement of the mechanical properties of a chromatin analog and the epigenetic effects of para-sulphonato-calix[4]arene

International audienceBy means of Silicon Nano Tweezers (SNTs) the effects on the mechanical properties of λ-phage DNA during interaction with calf thymus nucleosome to form an artificial chromatin analog were measured. At a concentration of 100 nM, a nucleosome solution induced a strong stiffening effect on DNA (1.1 N m −1). This can be compared to the effects of the histone proteins, H1, H2A, H3 where no changes in the mechanical properties of DNA were observed and the complex of the H3/H4 proteins where a smaller increase in the stiffness is observed (0.2 N m −1). Para-sulphonato-calix[4]arene, SC4, known for epigenetic activity by interacting specifically with the lysine groups of histone proteins, was studied for its effect on an artificial chromatin. Using a microfluidic SNT device, SC4 was titrated against the artificial chromatin, at a concentration of 1 mM in SC4 a considerable increase in stiffness, 15 N m −1 , was observed. Simultaneously optical microscopy showed a physical change in the DNA structure between the tips of the SNT device. Electronic and Atomic Force microscopy confirmed this structural rearrangement. Negative control experiments confirmed that these mechanical and physical effects were induced neither by the acidity of SC4 nor through nonspecific interactions of SC4 on DNA. With the recent and better knowledge on how gene regulation occurs and after intense debate in the academic community 1 , epigenetics has been commonly defined as "the study of changes in gene function that are mitoti-cally and/or meiotically heritable and that do not entail a change in DNA sequence" 2. Over the past years, epigenetics has been shown to play a central role in many different key functions at the cellular level, including differentiation, replication, and gene transcription 3. In a larger context, its contribution in physiological disorders has been revealed in cardio vascular illnesses, mental disorders and various cancers 4. Despite its inheritable character, epigenetics paradoxically possesses a reversible nature 5 that can be illustrated through its two main covalent modifications either directly on DNA with the methylation of cytosine nucleic bases or indirectly with various post translational modifications on proteins interacting with DNA such as histone proteins or other proteins called writers, erasers or readers 6. New therapeutic treatments are expected to target and reverse these modifications by inactivating the enzymes responsible for the deregulation of specific genes 7. Some inhibitors have been already approved by FDA, such as Azacitidine and Decitabine as DNA methyltrans-ferase inhibitors for the treatment of myelodysplastic syndrome 8 and Vorinostat and Romidepsin as inhibitors of histone deacetylase for the treatment of peripheral T-cell lymphoma 9. A new class of DNA artificial binders that directly block the methyllysine reading functions of reader enzymes in charge of conveying the methylation signal downstream has recently arisen as promising epigenetic drugs 10