New Study Sheds Light On Cellular Reprogramming
The transcription factor Oct4 is a protein that binds to DNA and controls the genes involved in reprogramming the cells. The team at EMBL Hamburg has now been able to resolve the crystal structure of Oct4 using high-intensity X-ray beams. In particular, their analysis focused on a previously unexplored linker sequence between two DNA binding elements of the protein. "The uniqueness of the linker has caught our attention for more than a decade and, thus, we are extremely pleased to see it for the first time, helping us rationalize its function in reprogramming cells to pluripotency" says Matthias Wilmanns who led the work in Hamburg.
The authors suggest that the linker recruits key partners to the Oct4 target genes, without whom the process of reprogramming cannot be completed. Colleagues at the Max Planck Institute for Molecular Biomedicine led by Hans Schöler supported these findings with studies on the modifications of the linker. They showed that changes in the sequence of the linker led to the loss of Oct4's reprogramming activity, and that a single residue mutation has major effects on the protein interface and thus affects the recruiting of key partners.
"Our work shows how unique the Oct4 interface is and how crucial it is for reprogramming to pluripotency. These are vital steps forward in our understanding of cell reprogramming and could lead us to new applications in the fields of drug discovery and tissue engineering" said Hans Schöler.
Ongoing research will help determine an integrated picture on how Oct4 acts in the context of many other protein components in stem cell pluripotency.
Terminally differentiated cells can be reprogrammed to pluripotency by the forced expression of Oct4, Sox2, Klf4, and c-Myc1-2. However, it remains unknown how this leads to the multitude of epigenetic changes observed during the reprogramming process. Interestingly, Oct4 is the only factor that cannot be replaced by other members of the same family to induce pluripotency3-5. To understand the unique role of Oct4 in reprogramming, we determined the structure of its POU domain bound to DNA. We show that the linker between the two DNAbinding domains is structured as an -helix and exposed to the protein's surface, in contrast to the unstructured linker of Oct1. Point mutations in this -helix alter or abolish the reprogramming activity of Oct4, but do not affect its other fundamental properties. Based on mass spectrometry studies of the interactome of wild-type and mutant Oct4, we propose that the linker functions as a protein-protein interaction interface and plays a crucial role during reprogramming by recruiting key epigenetic players to Oct4 target genes. Thus, we provide molecular insights to explain how Oct4 contributes to the reprogramming process.