MLL3 is a histone 3-lysine 4 methyltransferase with tumor-suppressor properties that belongs to a family of chromatin regulator genes potentially altered in neoplasia. Mutations in MLL3 were found in a whole genome analysis of colorectal cancer but have not been confirmed by a separate study.
The DNA hypomethylating drug decitabine (DAC) reactivates silenced gene expression in cancer and is approved for the treatment of the myelodysplastic syndrome. Gene reactivation after DAC is variable and incompletely understood. Here, we established a cell line system (YB5) derived from the SW48 colon cancer cell line to study DAC-induced reactivation. YB5 contains a hypermethylated cytomegalovirus promoter driving green fluorescent protein (GFP), and the locus is transcriptionally silent. GFP reexpression can be achieved by DAC treatment, but the expression level of individual cells is heterogeneous. DAC-treated YB5 cells were separated into GFP-positive and GFP-negative subpopulations. By comparing DAC-treated sorted GFP-positive and GFP-negative cells, we found that their methylation levels were similarly decreased but that histone modifications and histone H3 densities were remarkably different. Despite a similar degree of (incomplete) DNA hypomethylation, GFP-positive cells reverted to an active chromatin structure marked by higher H3K9 acetylation, lower H3K27 trimethylation, and lower promoter nucleosome density. GFP-negative cells had histone modifications and promoter nucleosome density, similar to parental cells. On DAC withdrawal, gradual resilencing and remethylation occurred in both GFP-positive and GFP-negative cells, and the resilencing correlated with a gradual increase in nucleosome occupancy in GFP-positive cells. These data show that hypomethylation alone after DAC is insufficient for gene expression induction, and that chromatin resetting to an active state including nucleosome eviction is required for activation of protein expression. Our findings suggest that gene expression is the key in optimizing DAC treatment strategies in the clinic.
There is discordance among studies assessing the impact of race on outcome of patients with Triple Negative Breast Cancer (TNBC). We assessed survival outcomes for African American (AA) versus Caucasian (CA) women with TNBC treated at an urban cancer center in Memphis, TN with a predominant AA patient population.
The current classification systems of myelodysplastic syndromes (MDS), including the International Prognostic Scoring System (IPSS), do not fully reflect the molecular heterogeneity of the disease. Molecular characterization may predict clinical outcome and help stratify patients for targeted therapies. Epigenetic therapy using decitabine, a DNA hypomethylating agent, is clinically effective for the treatment of MDS. Therefore, we investigated the association between DNA methylation and clinical outcome in MDS.
Epigenetic changes have been proposed as mediators of the field defect in colorectal carcinogenesis, which has implications for risk assessment and cancer prevention. As a test of this hypothesis, we evaluated the methylation status of eight genes (MINT1, 2, 31, MLH1, p16, p14, MGMT, and ESR1), as well as BRAF and KRAS mutations, in 57 multiple colorectal neoplasias (M-CRN) and compared these to 69 solitary colorectal cancers (S-CRC). There were no significant differences in methylation between M-CRNs and S-CRCs except for p14 and MGMT that was significantly higher in M-CRNs than S-CRCs (16.1% versus 9.3%; 26.5% versus 17.3%, respectively; P < 0.05). We found significant (P < 0.05) correlations for MINT1 (r = 0.8), p16 (r = 0.8), MLH1 (r = 0.9), and MGMT (r = 0.6) methylation between tumors pairs of the same site (proximal/proximal and distal/distal). KRAS showed no concordance in mutations. BRAF mutation showed concordance in proximal site pairs but was discordant in different site pairs. Histologically, eight of 10 paired cancers with similar locations were concordant for a cribriform glandular configuration. We conclude that synchronous colorectal tumors of the same site are highly concordant for methylation of multiple genes, BRAF mutations, and a cribriform glandular configuration, all consistent with a patient-specific predisposition to particular subtypes of colorectal cancers. Screening for and secondary prevention of colon cancer should take this fact into account.
Aberrant DNA methylation is an early and frequent process in gastric carcinogenesis and could be useful for detection of gastric neoplasia. We hypothesized that methylation analysis of DNA recovered from gastric washes could be used to detect gastric cancer.
Various therapeutic approaches for dysphagia management are based on modifications of bolus properties to change swallowing biomechanics and increase swallowing safety. Limited evidence exists for the effects of carbonation and bolus temperature on swallowing behavior. Here, we investigated the effects of carbonation and temperature on swallowing behavior using a novel automated and complex swallowing reaction time task via pressure signal recordings in the hypopharynx. Healthy participants (n = 39, 27.7±5 years old) were randomized in two different experiments and asked to perform 10 normal-paced swallows, 10 fast-paced swallows, and 10 challenged swallows within a predetermined time-window of carbonated versus still water (experiment 1) and of cold (4 °C) versus hot (45 °C) versus room temperature (21 °C) water (experiment 2). Quantitative measurements of latencies and percentage of successful challenged swallows were collected and analyzed nonparametrically. An increase in successfully performed challenged swallowing task was observed with carbonated water versus still water (P = 0.021), whereas only cold water shortened the latencies of normally paced swallows compared with room (P = 0.001) and hot (P = 0.004) temperatures. Therefore, it appears that chemothermal stimulation with carbonation and cold are most effective at modulating water swallowing, which in part is likely to be driven by central swallowing afferent activity.
DNA methylation is commonly thought of as a "molecular lock" that leads to permanent gene silencing. To investigate this notion, we tested 24 different histone deacetylase inhibitors (HDACi) on colon cancer cells that harbor a GFP locus stably integrated and silenced by a hypermethylated cytomegalovirus (CMV) promoter. We found that HDACi efficiently reactivated expression of GFP and many other endogenous genes silenced by DNA hypermethylation. After treatment, all promoters were marked with active chromatin, yet DNA hypermethylation did not change. Thus, DNA methylation could not prevent gene reactivation by drug-induced resetting of the chromatin state. In evaluating the relative contribution of DNA methylation and histone modifications to stable gene silencing, we followed expression levels of GFP and other genes silenced by DNA hypermethylation over time after treatment with HDACi or DNA-demethylating drugs. Reactivation of methylated loci by HDACi was detectable for only 2 weeks, whereas DNA-demethylating drugs induced permanent epigenetic reprogramming. Therefore, DNA methylation cannot be considered as a lock for gene expression but rather as a memory signal for long-term maintenance of gene silencing. These findings define chromatin as an important druggable target for cancer epigenetic therapy and suggest that removal of DNA methylation signals is required to achieve long-term gene reactivation.
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