One hypothesis is that CpG island hypermethylation of TSGs is driven by a mechanism involving unknown DNA binding factors that selectively recruit DNMT1 to the promoters of TSGs which will lead to pathological hypermethylation and subsequently to unpaired apoptosis. Many evidences of the crosstalk between DNA methylation and histone modifications have been reported [24, 25]. The most important histones modifications, having effects on gene expression, are
located on histone H3 and histone H4 . One of them, that is known to have a gene silencing role and to have a strong relationship Adriamycin with DNA methylation, is the di- or tri-methylation of lysine 9 of histone 3 (H3K9me2 or H3K9me3). But methylation on the same histone on lysine 4 (H3K4me) is related to gene activation. All
these modifications are catalysed by a broad variety of HDAC inhibitor specific enzymes, some of which can catalyse the same reaction but at different location in the nucleus, i.e., heterochromatin or euchromatin . Histones undergo specific changes in their acetylation and methylation degrees during cancerogenesis . Both deacetylation of H4K16 and accumulation of H3K9me2 are found on many repressed genes, including TSGs [27, 28]. These modifications are mediated by HDACs (histone deacetylases) and G9a (histone 3 methyltransferase) respectively. HDACs are often over-expressed in various types of cancer such as renal cancer  or gastric cancer  and have become essential targets for anticancer therapy. G9a is co-localized near the methylated promoters of numerous genes in cancer cells . Interestingly, it has been found that the inhibition of G9a is sufficient to induce a reactivation
of TSGs . Therefore, over-expression of enzymes catalysing histone modifications (epigenetic writers), might be one explanation for the occurrence of altered epigenetic marks found in cancer. There is increasing evidence that Ubiquitin-like Pembrolizumab containing PHD Ring Finger 1 (UHRF1, also known as ICBP90 or Np95) plays a fundamental role in these processes by being involved in DNA methylation, histone methylation, histone acetylation, cell proliferation and apoptosis. This is due to the fact that UHRF1 possesses several domains (Figure 1) able to read both DNA methylation and histone methylation, thus, physically linking these two epigenetic marks [26, 33, 34]. Figure 1 Schematic representation of UHRF1 with the structural domains facing either DNA or histones. Abbreviation: UBL, Ubiquitin-like domain; TTD, cryptic Tandem Tudor Domain; PHD, Plant Homeo Domain; SRA, Set and Ring Associated; RING, Really Interesting New Gene. The major partners of UHRF1, namely Tat-Interactive Protein of 60 kDA (Tip60), DNA methyltransferase 1 (DNMT1), histone methyltransferase G9a (G9a) and Histone DeAcetylase (HDAC1) are also depicted. 3.