Statement of Benefit to California:
Year 1Human embryonic stem cells (hESCs) hold promise for treating a broad range of human diseases. However, at the time when we submitted this proposal, there was a striking paucity of published studies on how the fate of hESCs is controlled. For instance, we know that hESCs can form tumors upon transplantation, but the mechanisms governing cell division in these cells were still largely unknown. Given the central role of the retinoblastoma (RB) family of genes at the interface between proliferation and differentiation, our goal was to study the function of RB and its family members p107 and p130 in human embryonic stem cells (hESCs). In the last two years, we have examined the consequences of altering the function of RB, p107, and p130 for the proliferation, self-renewal, and differentiation potential of hESCs.
We have found that overexpression of RB results in cell cycle arrest in hESC populations, indicating that the RB pathway can be functionally activated in these cells. We have also found that loss of RB function does not result in significant changes in the biology of hESCs. In contrast, inactivation of several RB family members at the same time leads to self-renewal, proliferation, and differentiation defects.
Together, these studies indicate that the level of activity of the RB family is critical in hESCs: too much or too little RB family function results in loss of proliferative potential.
Our future goal is to precisely manipulate the levels of RB family genes to determine if we can identify conditions to manipulate the fate of hESCs, reducing their ability to proliferate (suppressing cancer) while allowing them to differentiate into specific lineages.