From Gametogenesis to Oncogenesis: The Many Roles of DDX1

• Author / Creator

  Germain, Devon Roy

• DEAD box proteins are a family of RNA helicases implicated in every aspect of RNA biogenesis and metabolism. Modification of RNA secondary structure by DEAD box proteins has widespread effects on numerous cellular processes due to the ubiquitous nature of RNA. While the biochemical activity of several DEAD box proteins has been described, there is limited information into the biological functions of most family members. DEAD box 1 (DDX1) is over-expressed in some cancers, and has in vitro RNA/RNA and RNA/DNA unwinding activity. In vivo analyses have implicated DDX1 in RNA maturation, double-stranded DNA damage response and viral maturation. To date, there have been no reported DDX1-negative cell lines, with neuronal and germline cells showing the highest DDX1 levels. Here, we describe three novel facets of DDX1 biology and function. First, we report that DDX1 is a novel and independent prognostic indicator in breast cancer. Both increased DDX1 mRNA levels and cytoplasmic DDX1 protein localization are negative prognostic markers. Analysis of treatment-specific subgroups revealed that this effect is elevated in patients who receive adjuvant therapy, indicating that DDX1 may be predictive of patient response to treatment. Second, we report the generation of a novel Ddx1-null allele in Drosophila melanogaster. Ddx1-null flies are viable, but have phenotypes consistent with reduced metabolism and display aberrant gametogenesis. We also describe an interaction between Ddx1 and Sirup mRNA, which may underlie the metabolic disruption observed in mutant Ddx1 flies. Third, we have found that Ddx1-/- mice die at the pre-blastocyst stage. We also observed that mice carrying one Ddx1- allele display transgenerational inheritance, with heterozygous Ddx1 mice generated from heterozygous intercrosses producing significantly fewer wild-type progeny than expected. We attribute this to a novel modification of the wild-type allele in heterozygous mice and demonstrate that transgenerational inheritance of Ddx1 is distinct from previously described cases of transgenerational epigenetic inheritance. These combined studies address different aspects of DDX1 function, providing new insight into the spectrum of biological roles associated with DDX1. DDX1 appears to be under strict regulation, as evidenced by the fact that Ddx1 levels in mice do not vary between heterozygous and wild-type animals. Strict regulation of DDX1 levels may explain why prognostic effects are observed when DDX1 levels are elevated in breast cancer. Although we did not attempt to determine why high levels of DDX1 are associated with early recurrence, the phenotypes observed in our Ddx1-null flies suggest a role for Ddx1 in regulating metabolism. We propose that DDX1 is an integral regulator of metabolism and growth, and is itself tightly regulated. As such, deregulation of DDX1 can either promote tumourigenesis (when over-expressed) or death (when absent). This model of DDX1 action indicates that it may be possible to target DDX1 to improve patient outcome in those cancer patients with mis-expressed DDX1.

• Subjects / Keywords

  • Oncogenesis
  • Gametogenesis
  • DDX1
  • Transgenerational epigenetics

• Graduation date

  Fall 2015

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3KP7TW9M

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.