Characterization of the Human Dead-Box RNA Helicase DDX5
Gene expression in eukaryotes is highly complex. The central player in gene expression is the messenger RNA (mRNA). After transcription, the mRNA is bound by numerous RNA binding proteins to form a messenger ribonucleoprotein complex (mRNP) that dictates the function and fate of the messengers. Proper mRNP formation is critical for gene expression. DEAD-box proteins are the largest class of RNA helicases that play fundamental roles in RNA and RNP structure remodeling. However, the precise biological roles of the vast majority of them are not well described. To fill in this gap, my research focused on the characterization of the DDX5/Dbp2 subfamily of DEAD-box proteins in gene expression, cellular metabolism, and carcinogenesis. My research revealed that DDX5 is an active helicase in vitro. DDX5 has higher RNA unwinding activities as compared to Dbp2, consistent with longer RNAs and more complex RNA structures in mammalian cells. Distinct from Dbp2, DDX5 lacks duplex annealing activities in vitro, which may contribute to faster unwinding. Despite differences in enzymatic activities, DDX5 complements the growth defects and cryptic transcription of the dbp2Δ Saccharomyces cerevisiae strain, indicating that DDX5 and Dbp2 are funcitonally conserved. Interestingly, Dbp2 and DDX5 are both involved in glucose metabolism. dbp2Δ yeast displays reduced glucose uptake and increased respiration. Consistent with this, depletion of DDX5 in the hepatocyte cell line AML12 leads to downregulation of glycolysis and upregulation of respiration, indicating that DDX5 is a positive regulator of glycolysis in mammalian cells. Glycolysis is a key process to maintain cellular energy homeostasis and is elevated in cancer cells (i.e. the Warburg effect). Furthermore, DDX5 is frequently overexpressed in cancers. Therefore, DDX5 may function to fulfill the energy requirement of cancer cells. Future research will examine this hypothesis.
Tran, Purdue University.
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