Epigenetic mechanisms and regulatory aspects of human cancer and neural progenitor cells : implications for diagnosis and therapy

Abstract: Epigenetic is defined as heritable modification or properties of the functional genome that are not directly embedded in the DNA sequence. Epigenetic changes include DNA methylation, histone modifications and RNA-mediated gene silencing. Genomic imprinting is a mechanism of allele-specific epigenetic control of gene expression according to parent of origin. Alteration of genomic imprinting is associated with tumorigenesis. This thesis is aimed to study epigenetic aspects of human cancer like adrenocortical carcinoma, human cancer cell line, Hep3B and JEG-3 and neural progenitor cells. In study I we have investigated the effect of histone deacetylase inhibitor (HDACi), 4- PB on the gap junctional communication between neuronal progenitor cells (NPC) and glioblastoma multiforme (GBM) cells involving connexin 43 (Cx43). 4-PB increased Cx43 in-vitro, and NPCs may be used as a delivery vehicle for enzyme prodrug therapy for GBM. The purpose of study II was to explore the regulation of neural stem cell differentiation by 4-PB involving de novo DNA methyltransferase DNMT3B. For this study we used human embryonic stem cells, NGC-407. Treatment of the human embryonic stem cells, NGC-407 with 4-PB, suppressed astrocytic and neuronal differentiation along with DNMT3B immunoreactivity. This suggests that 4-PB preserve the immature phenotype of NGC-407 by involving epigenetic mechanism of de novo methylation. In study III we examined the role of transcription factor PLAG1 on IGF2 P3 promoter regulation in human cancer cell lines Hep3B and JEG-3. We also studied the ability of PLAG1 to override the insulator effect of the H19 Imprinting Control Region (ICR) in a GFP reporter construct. We conclude that PLAG1 binding to the IGF2 P3 promoter is cell line specific and PLAG1 acts as a transcriptional facilitator to partially override the insulation at H19 ICR. In study IV we identified associations of proteomic profiles with aberration of H19/IGF2 locus in adrenocortical malignancy. Proteomic profiles were acquired from ACAs and ACCs. We revealed that IGF2, along with miR-483-3P and miR-483-5P overexpression in ACCs, is associated with tumor-type specific proteome profiles. We have shown a positive correlation between IGF2 and its miR-483-3P and miR-483-5P along with H19 and its miR-675. We suggest that specific proteomes associated with microRNAs in the H19/IGF2 locus in ACCs may be used as therapeutic markers and patient follow-up.