Human embryonic stem cells (hESCs) have the remarkable capacity of limitless self-renewal. This property is known to be controlled by signaling of a growth factor called Wnt. This proposal investigates the molecular mechanism by which Wnt causes self-renewal. Current conversational wisdom is that Wnt only prolongs the half-life of a protein called β-Catenin.
Here we propose the hypothesis that Wnt regulates the stability of a multitude of proteins, all of them characterized by receiving phosphates from an enzyme called Glycogen Synthase Kinase 3 (GSK3). In this view, Wnt would be a general metabolic signal that instructs cells to slow down protein degradation by inhibiting GSK3 activity.
How is GSK3 inhibition achieved? This is a key unanswered question in the Wnt signaling field. We propose a new cellular mechanism by which the GSK3 enzyme is sequestered inside intracellular vesicular organelles (called multivesicular bodies) after Wnt signaling. If this GSK3 sequestration hypothesis can be proven, it would constitute an important contribution to stem cell research.
Human embryonic stem cells are essential for these investigations because they naturally have very high levels of Wnt signaling. In addition, they have asymmetric mitotic divisions. We will develop methods to investigate why some hESCs differentiate, losing their astonishing self-renewal potential. The experiments proposed will help understand how Wnt signaling maintains the pluripotent state in hESCs.
By investigating the hypothesis that Wnt signaling functions as a general regulator of protein stability, we hope to significantly advance the field of human embryonic stem cell research and regenerative medicine.
The State of California benefits from the proposed basic research by strengthening its leadership role in worldwide stem cell research. This project would provide employment for five full-time researchers, who will obtain training in cutting-edge molecular and cell biology research.
It has been our experience that trainees leave our laboratory always for better high-tech jobs. Many go into the biotech industry and others into teaching at the college level. Funding this project will benefit California by producing an improved and highly trained workforce. It will also strengthen our already excellent university research system.