No abstract

Nuclear β-dystroglycan (β-DG) is involved in the maintenance of nuclear architecture and function. Nonetheless, its relevance in defined nuclear processes remains to be determined. In this study we generated a C2C12 cell-based DG-null model using CRISPR-Cas9 technology to provide insights into the role of β-DG on nuclear processes. Since DG-null cells exhibited decreased levels of lamin B1, we aimed to elucidate the contribution of DG to senescence, owing to the central role of lamin B1 in this pathway. Remarkably, the lack of DG enables C2C12 cells to acquire senescent features, including cell-cycle arrest, increased senescence-associated-β-galactosidase activity, heterochromatin loss, aberrant nuclear morphology and nucleolar disruption. We demonstrated that genomic instability is one driving cause of the senescent phenotype in DG-null cells via the activation of a DNA-damage response associated with mitotic failure, as shown by the presence of multipolar mitotic spindles, which in turn induced the formation of micronuclei and γH2AX foci (DNA-damage marker), telomere shortening and p53/p21 upregulation. Altogether, these events might ultimately lead to premature senescence, impeding the replication of the damaged genome. In summary, we present evidence supporting a role for DG in protecting against senescence, through the maintenance of proper lamin B1 expression/localization and proper mitotic spindle organization.

The association between the downregulation of genes and DNA methylation in their CpG islands has been extensively studied as a mechanism that favors carcinogenesis. The objective of this study was to analyze the methylation of a set of genes selected based on their microarray expression profiles during the process of hepatocarcinogenesis. Rats were euthanized at: 24 h, 7, 11, 16 and 30 days and 5, 9, 12 and 18 months post-treatment. We evaluated the methylation status in the CpG islands of four deregulated genes (Casp3, Cldn1, Pex11a and Nox4) using methylation-sensitive high-resolution melting technology for the samples obtained from different stages of hepatocarcinogenesis. We did not observe methylation in Casp3, Cldn1 or Pex11a. However, Nox4 exhibited altered methylation patterns, reaching a maximum of 10%, even during the early stages of hepatocarcinogenesis. We observed downregulation of mRNA and protein of Nox4 (97.5% and 40%, respectively) after the first carcinogenic stimulus relative to the untreated samples. Our results suggest that Nox4 downregulation is associated with DNA methylation of the CpG island in its promoter. We propose that methylation is a mechanism that can silence the expression of Nox4, which could contribute to the acquisition of neoplastic characteristics during hepatocarcinogenesis in rats.

No abstract

The most important mutation associated with Multiple Endocrine Neoplasia type 2B (MEN 2B) is the change of thymine to cytosine in codon 918 of exon 16 in the RET oncogene (ATG → ACG). The aim of this work was to develop a single oligoarray by using tandem hybridization to detect the T918C/RET mutation for MEN 2B patients. Two genetically non-related families were studied; each family had a member affected by MEN2B. Both patients presented the T918C/RET mutation in a heterozygous fashion. None of the relatives was positive for this mutation; thus, these cases arose de novo. The proper mutation was confirmed by with different tools, PCR-Fok I endonuclease, direct sequencing, and also using our oligoarray. In this case, it is suitable to use a DNA target smaller than 150 bases with single- or double-stranded DNA and short probes of 7-mer. It was also possible to detect the mutation by employing different sources of DNA, fresh or paraffin-embedded tissues. Therefore, the present oligoarray can identify the most common M918T mutation of RET oncogene from a variety of DNA sources with good specificity and be a good alternative in the molecular diagnosis for MEN 2B cases.