Causes and consequences of altered microRNA levels. Regulation of microRNA and identification of microRNA-155 target genes

PhD ceremony: Ms. I.H. Slezak-Prochazka, 10.15 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: Causes and consequences of altered microRNA levels. Regulation of microRNA and identification of microRNA-155 target genes

Promotor(s): prof. J.H.M. van den Berg

Faculty: Medical Sciences

MiRNAs are effective gene expression regulators that play crucial roles in most cellular processes. Altered miRNA levels are observed in almost all types of B-cell lymphoma. The aim of this thesis is to investigate possible causes of altered miRNA levels and the consequences of altered miRNA-155 levels in B-cell lymphoma. We present an overview of established mechanisms to regulate miRNA processing. We next studied processing of a relatively small group of miRNAs that are located in exons of noncoding RNAs. Based on subcellular location and overexpression experiments we concluded that miRNAs are processed predominantly from the unspliced transcripts that almost completely reside in the nucleus. We studied processing of the oncogenic miR-17~92 cluster in normal B cell subsets and in four B-cell non-Hodgkin lymphoma (NHL) subtypes. We observed marked differences between the levels of the six miRNAs in the B cell subsets and the NHL subtype. In comparison to their normal counterparts, all lymphoma subtypes showed a marked induction of miR-19b. We describe a straight-forward method to generate viral miRNA sponge constructs that can be used to inhibit miRNA functioning. Finally, we studied the consequences of altered miR-155 expression levels in B-cell lymphoma. Induction of miR-155 revealed a significant growth advantage of the tumor cells. Using Ago2-RIP-Chip and phenotype copy experiments we showed that TBRG1 is one of the miR-155 targets. Inhibition of TBRG1 also induced a growth advantage similar to the miR-155 effect.