Molecular mechanisms connecting signal transduction and RNA processing: Structural studies of the STAR family of protein

Lead Research Organisation: University of Leicester
Department Name: Biochemistry


Post-transcriptional gene regulation is a major regulatory event in cells that allow for protein diversity out of a limited number of genes. These regulations are modulated by extracellular signals through cell signalling. Very little is known about the molecular mechanisms that govern these regulations and modulations. I intend to study at a molecular level a family of proteins, called STAR, which connects cell signalling and post-transcriptional gene regulation. For that I will use a combination of biochemical and biophysical methods, especially NMR spectroscopy. The first main aspect of the project will be to characterize structurally how STAR proteins specifically recognize their target RNAs. The second aspect will involve protein-protein interactions and will be to characterize how cell signalling affects the functions of these proteins in post-transcriptional gene regulation.
Since these proteins play a role in tumour progression and in the life cycle of retroviruses, like HIV-1, these structural studies will provide the molecular basis for developing specific drugs optimized for cancer and retroviral therapies.

Technical Summary

Cellular processes are tightly regulated at different levels by various signaling pathways depending on extracellular stimulations. I aim at better understanding the interplay between signaling pathways and post-transcriptional gene regulation. Post-transcriptional gene regulation consists of major events in cells, such as alternative splicing, RNA export, or translation regulation, that are still not fully understood. The project I intend to develop seeks at unraveling at the molecular level the functional properties of the STAR (Signal Transduction and Activation of RNA) family of protein. These proteins provide a direct connection between cell signaling and post-transcriptional modifications.

The STAR family is involved in many cellular processes such as signal transduction, post-transcriptional gene regulation, tumorigenesis and viral metabolism. All these proteins are involved in the regulation of alternative splicing and RNA export. Importantly, Sam68, the best characterized member of this family, has important roles in post-transcriptional gene regulation that are connected with tumor progression and retroviral life cycle.

STAR proteins contain a STAR domain responsible for RNA binding, several proline and tyrosine rich sequences that promote phosphorylation by diverse kinases, arginine-glycine rich sequences that are methylated by methyltransferase enzymes, and nuclear localization signals allowing the protein to shuttle between the nucleus and the cytoplasm.

There are no structures of a full STAR domain free or in complex with RNA. I therefore plan to solve the NMR structures of STAR domains of different STAR proteins free and in complex with their RNA targets in order to define a general mechanism for RNA recognition by STAR family members. In addition, Sam68 regulate the export of HIV-1 RNAs by binding the viral RNA and the Rev protein. I plan to study biochemically and structurally the trimolecular complex formed between Sam68, Rev and the HIV-1 RNA.

Phosphorylation and arginine methylation of STAR proteins affect their RNA binding capability and therefore their functions in post-transcriptional gene regulation. An aspect of the project will be to study structurally theses domains in complex with signaling molecules to understand how post-translational modifications are achieved in STAR proteins and how these modifications affect the RNA binding capacities.

Summarizing, I will apply my knowledge of molecular biology, biochemistry, NMR, protein/RNA structural biology, and docking to unravel the structural properties of the STAR family. Since STAR proteins play an important role in tumor progression and HIV RNA export, these structural studies will help initiating application for optimized viral and cancer therapies.


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