Eukaryotic gene expression is a fundamental cellular activity that is critical for cellular identity, function, and physiology. During gene expression, a messenger RNA (mRNA) is generated by transcription and undergoes a number of different steps, including splicing and nuclear processing, nucleocytoplasmic export and localization, translation, and decay (Figure 1). These steps result in dynamic changes to the RNA sequence, structure, and the cohort of proteins bound to the mRNA. Furthermore, these changes need to occur with the proper timing and in the correct sequence to avoid aberrant expression. Therefore elaborate regulation of mRNP dynamics is required for proper gene expression.

At virtually every step in gene expression, members of a highly conserved protein family called the DEAD-box proteins are required for facilitating mRNP transitions by acting as RNA helicases and ribonucleoprotein (RNP) remodeling enzymes. Therefore, DEAD-box helicases function as master regulators of RNA and RNA-protein interactions during gene expression (and other RNA-dependent cellular processes), exerting overarching control of RNP dynamics. However, how they control different subsets of mRNAs, particularly in response to different cellular conditions, is still largely unclear.

We and others have described a novel role for Ded1 in regulating translation during cellular stresses such as lack of nutrients, extreme temperatures, or oxidative stress. Interestingly, Ded1 represses translation in stress, unlike its stimulatory role in pro-growth conditions (Figure 3). We have shown that Ded1 causes dissociation of its binding partner eIF4G1 from translation complexes, leading to degradation of both eIF4G1 and Ded1. We are currently examining the effects of Ded1 on other parts of the translation machinery in stress. Furthermore, we have recently begun identifying the translational targets of Ded1 during stress responses and how these may differ between different kinds of stresses.

Many cellular pathways and processes are involved in responding to stress conditions. In order to examine how translation regulation is connected to these other pathways, we performed a genome-wide screen for interactions with DED1 during stress conditions (Figure 4). Among other results,  we identified stress-dependent genetic interactions with genes that regulate the cell cycle, suggesting a functional link between translation and the cell cycle during stress. We are currently working to follow up these results as well as other candidates from the screen in order to better understand the cellular stress response.

Genome sequencing studies have found frequent mutations in DDX3X in medulloblastoma, the most common pediatric brain cancer. Dysregulation of translation has the potential to greatly enhance cancer progression; however, it remains largely unclear how the DDX3X mutations contribute to cancer. We have analyzed the effects of a large set of the mutants, and have found that they cause mRNA-specific changes in translation, upregulating some while downregulating others. We propose that these alterations allow cancer cells to bypass normal stress responses and continue growing in adverse conditions. We are now moving to medulloblastoma cell lines to examine the phenotypes we observed in that system.