Div. of Medical Oncology Dept. of Internal Medicine Dept. of Pathology GROW-School for Oncology and Developmental Biology Maastricht University Medical Center P.O. Box 616 6200 MD Maastricht The Netherlands
Abstract: Recently, DNA methylation has been suggested as a potential mechanism involved in the transcriptional regulation of SHH gene expression in cancer. However, detailed analyses on the underlying transcriptional mechanisms of SHH expression have not been presented so far and were therefore the focus of this study. We found that the genomic region of SHH contains two different transcriptional start sites and four CpG islands spread from the 5`promoter region to the 3`end of the SHH gene. Based on this CpG island topology we analyzed the influence of DNA methylation within the promoter region as well as in exon 2 and exon 3 on SHH mRNA expression in a large set (n=14) of benign and malignant human cell lines and further elucidated the functionality of the two identified SHH transcription initiation sites. Methylation-specific PCR (MSP) clearly showed that SHH is expressed independently of DNA methylation within exon 2 and exon 3 of its genomic region while methylation of the promoter region is able to abrogate SHH expression. Most interesting, we found activation of the upstream SHH promoter in several breast cancer cell lines, when the downstream SHH promoter is methylated. These observations lead us to propose a transcriptional model for the SHH gene, in which combined mechanisms of DNA methylation and alternative promoter usage coordinate the transcriptional activity of this important developmental gene.
Abstract: Triple-negative breast cancers (TNBC) neither express hormone receptors, nor overexpress HER2. They are associated with poor prognosis, as defined by low five-year survival and high recurrence rates after adjuvant therapy. Overall, TNBC share striking similarities with basal-like breast cancers (BBC), so a number of studies considered them being the same. The purpose of this review is to summarise the latest findings on TNBC concerning its relation and delineation to BBC, discuss the developmental pathways involved and address clinical implications for this complex type of breast cancer.
Abstract: Identification of hypermethylated tumor suppressor genes in body fluids is an appealing strategy for the noninvasive detection of colorectal cancer. Here we examined the role of N-Myc downstream-regulated gene 4 (NDRG4) as a novel tumor suppressor and biomarker in colorectal cancer.
Abstract: Nucleotide excision repair (NER) mainly repairs bulky DNA adducts and helix distorting lesions, but is additionally considered to be a back-up system for base excision repair to remove oxidative stress induced DNA damage. Therefore, it can be speculated that NER is up-regulated or primed by oxidative stress. Exposure of human pulmonary epithelial cells (A549) to non-toxic doses of 100muM H(2)O(2) indeed showed a 2 to 4.5-fold increase in expression of XPA, XPC, ERCC4, and ERCC5, whereas the expression of ERCC1 was 5-fold decreased. Phenotypical assessment of NER capacity (i.e. recognition and incision of benzo[a]pyrene-DNA adducts) showed a significant decrease to less than 50% after H(2)O(2) exposure, which paralleled the effects of H(2)O(2) on ERCC1 expression. To study the possible involvement of glutathione (GSH) in the regulation of NER, cells were pre-incubated with 0.5mM BSO, resulting in total GSH depletion and increased intracellular oxidative stress. In GSH-depleted cells, the down-regulation of ERCC1 expression by H(2)O(2) was completely abolished and the up-regulation of ERCC4 expression was potentiated from 2.5-fold to >10-fold. Similarly, the H(2)O(2)-induced decrease in NER capacity was absent in GSH-depleted cells. Overall, our data suggest that NER capacity as well as the expression of NER related genes can be modulated by oxidative stress. ERCC1 expression and NER capacity correlated strongly (R(2)=0.85, P<0.01) after oxidant exposure, indicating ERCC1 as a specific target for oxidative stress induced modification of NER.
