Promoter epigenetics of APC gene and its implication in sporadic breast cancer patients from South Indian population

Methylation analysis of histone 4-related gene HIST1H4F and its effect on gene expression in bladder cancer

Recently, aberrant DNA methylation of the HIST1H4F gene (encodes Histone 4 protein) has been shown in many types of cancer, which may serve as a promising biomarker for early cancer diagnosis. However, the correlation between DNA methylation of the HIST1H4F gene and its role in gene expression is unclear in bladder cancer. Therefore, the first objective of this study is to explore the DNA methylation pattern of the HIST1H4F gene and then further elucidate its effects on HIST1H4F mRNA expression in bladder cancer. To this end, the methylation pattern of the HIST1H4F gene was analyzed by pyrosequencing and the effects of the methylation profiles of this gene on HIST1H4F mRNA expression in bladder cancer were examined by qRT-PCR. Sequencing analysis revealed significantly higher methylation frequencies of the HIST1H4F gene in bladder tumor samples compared to normal samples (p < 0,0001). However, when we evaluated the correlations between hypermethylation of HIST1H4F and the clinicopathological parameters (tumor stage, tumor grade, lymph node metastasis, muscle-invasion), no significant difference was found between the groups (p > 0.05). In addition, we examined the role of hypermethylation of the HIST1H4F gene on HIST1H4F mRNA expression. We found that hypermethylation of HIST1H4F in the exon have no effect HIST1H4F mRNA expression in bladder cancer (p > 0.05). We also confirmed our finding in cultured T24 cell line which HIST1H4F gene is hypermethylated. Our results suggest that hypermethylation of the HIST1H4F seems to be a promising early diagnostic biomarker in bladder cancer patients. However, further studies are needed to determine the role of HIST1H4F hypermethylation in tumorigenesis.

Homologous Recombination Deficiency in Ovarian, Breast, Colorectal, Pancreatic, Non-Small Cell Lung and Prostate Cancers, and the Mechanisms of Resistance to PARP Inhibitors

Homologous recombination (HR) is a highly conserved DNA repair mechanism that protects cells from exogenous and endogenous DNA damage. Breast cancer 1 (BRCA1) and breast cancer 2 (BRCA2) play an important role in the HR repair pathway by interacting with other DNA repair proteins such as Fanconi anemia (FA) proteins, ATM, RAD51, PALB2, MRE11A, RAD50, and NBN. These pathways are frequently aberrant in cancer, leading to the accumulation of DNA damage and genomic instability known as homologous recombination deficiency (HRD). HRD can be caused by chromosomal and subchromosomal aberrations, as well as by epigenetic inactivation of tumor suppressor gene promoters. Deficiency in one or more HR genes increases the risk of many malignancies. Another conserved mechanism involved in the repair of DNA single-strand breaks (SSBs) is base excision repair, in which poly (ADP-ribose) polymerase (PARP) enzymes play an important role. PARP inhibitors (PARPIs) convert SSBs to more cytotoxic double-strand breaks, which are repaired in HR-proficient cells, but remain unrepaired in HRD. The blockade of both HR and base excision repair pathways is the basis of PARPI therapy. The use of PARPIs can be expanded to sporadic cancers displaying the “BRCAness” phenotype. Although PARPIs are effective in many cancers, their efficacy is limited by the development of resistance. In this review, we summarize the prevalence of HRD due to mutation, loss of heterozygosity, and promoter hypermethylation of 35 DNA repair genes in ovarian, breast, colorectal, pancreatic, non-small cell lung cancer, and prostate cancer. The underlying mechanisms and strategies to overcome PARPI resistance are also discussed.