Defense Date


Document Type


Degree Name

Doctor of Philosophy


Human Genetics

First Advisor

Paul B. Fisher


RNA degradation plays a fundamental role in maintaining cellular homeostasis, along with being a part of normal regulatory mechanisms, whether it occurs as a surveillance mechanism eliminating aberrant mRNAs or during RNA processing to generate mature transcripts. 3’-5’ exoribonucleases are essential mediators of RNA decay pathways, and one such evolutionarily conserved enzyme is polynucleotide phosphorylase (PNPase). The human homologue of this fascinating enzymatic protein (hPNPaseold-35) was cloned a decade ago in the context of terminal differentiation and senescence through a novel ‘overlapping pathway screening’ approach. Since then, significant insights have been garnered about this exoribonuclease and its repertoire of expanding functions. hPNPaseold-35 has progressed a long way from being just a 3’-5’ exoribonuclease to a functionally relevant molecule implicated in a multitude of diverse and important biological effects. hPNPaseold-35 plays central roles in diverse physiological processes including growth inhibition, senescence, mtRNA import, mitochondrial homeostasis, and RNA degradation, all while primarily being localized in the mitochondrial IMS (inter membrane space). hPNPaseold-35 also holds immense promise as a therapeutic agent due to its ability to degrade specific miRNA (miR-221) and mRNA (c-myc) species, and this property can be exploited in treating malignancies that are characterized by upregulation of harmful miRNA or mRNA molecules. But apart from these two targets, little is known about any other targets hPNPaseold-35 may degrade. Thus, the primary objective of this dissertation research was to identify targets other than c-myc or miR-221 that hPNPaseold-35 could directly degrade to discover newer and biologically relevant therapeutic targets for the treatment of hPNPaseold-35 –associated disease states. In order to do this we performed extensive microarray analyses following hPNPaseold-35 overexpression and depletion in mammalian cell lines, and were able to identify transcripts that could be potentially regulated by hPNPaseold-35 directly or indirectly. Apart from this we also analyzed the 3’UTR of c-myc in order to identify any specific sequence or secondary structural elements necessary for hPNPaseold-35 mediated degradation. Lastly, we identified certain residues in hPNPaseold-35 that have been under positive natural selection through evolution.


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Is Part Of

VCU University Archives

Is Part Of

VCU Theses and Dissertations

Date of Submission

December 2013