Basic Biology I
One important aspect of regenerative medicine is the ability to introduce functional stem cells into patients to restore tissue function. This type of therapeutic approach will not be commonly used until several major potential problems have been addressed, including immune rejection and the risk of developing cancer. Induced pluripotent stem cells (iPSCs) hold great promise in regenerative medicine: these cells are similar to embryonic stem cells (ESCs) but can be derived upon “reprogramming” of any mature cell type isolated from a patient. Thus, tissue-specific stem cells derived from iPSCs and re-injected into the same patient may not trigger immune rejection. However, before the full potential of iPSCs is achieved, we need to learn how to better generate these cells, control their maturation into tissue-specific stem cells and progenitors, and harness their tumorigenic potential. Interestingly, ESCs and iPSCs share many characteristics of cancer cells, including their unlimited proliferation potential, and emerging evidence suggests that the mechanisms underlying the infinite proliferation of cancer cells and ESCs are intimately intertwined. Similarly, the progressions stages of tumorigenesis and cellular reprogramming to iPSCs share several characteristics, including changes in the packaging of the chromosomes. Based on these observations, we propose to directly study the function of a major cancer pathway, the RB pathway, in cellular reprogramming and iPSCs. RB is a key tumor suppressor in humans. RB acts as a cellular brake that restricts cell division but has several other cellular functions, including in the control of cellular maturation. When RB is mutated, cells divide faster and become more immature, two features of cancer cells, but also of cells undergoing reprogramming. We hypothesize that RB is an important regulator of cellular reprogramming and will test this idea using mouse and human cell types in culture. We believe that these experiments may identify novel and safer ways to induce the generation of iPSCs from adult cells or to improve existing protocols. Understanding the molecular details of the reprogramming process may lead to the development of small molecule compounds that can target precise proteins and/or transcription machinery involved in reprogramming. These experiments may also provide novel insights into the differences and similarities between tumor cells and iPSCs, providing new ways to suppress the tumorigenic potential of iPSCs and ESCs. Finally, better knowledge of the mode of action of RB family members may also allow for a better control of the differentiation of hESCs and iPSCs into tissue-specific stem cell populations.
Statement of Benefit to California:
Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) hold the promise of treatments and cures for human diseases that affect millions of people. However, before these cells can be used in the clinic, a better understanding of the mechanisms controlling their proliferation and their capacity to produce a functional progeny is critically required. Our work on how the RB tumor suppressor gene may control the reprogramming of somatic cells into iPSCs may identify novel means to manipulate hESCs, to control the fate of these cells when transplanted into patients. Because hESCs have the capacity to form any type of cell in the human body, these experiments will be relevant to a large number of human diseases. Despite significant decreases in the incidence and mortality rates of cancers in California over the past decade, nearly one out of every two Californians born today will still develop cancer at some point in their lives, and it is likely that one in five persons will die of the disease. Overall, in 2009, more than 50,000 people will die of cancer in California. These statistics underscore the need for the development of novel approaches to detect and treat human cancers. Given the similarities between tumor cells and embryonic cells, our work on the role of the RB tumor suppressor in hESCs and iPSCs may provide novel insights into the mode of action of RB in human cancer cells and may identify novel means to detect and treat cancer patients. Thus, the proposed research may benefit a broad range of patients, from young children to senior citizens, in California and elsewhere.
The goal of this proposal is to understand mechanisms by which the retinoblastoma (Rb) gene family regulates stem cell pluripotency, self-renewal, and tumorigenesis. Rb acts as a cellular brake that restricts cell division, but the protein has several other cellular functions including the control of cellular maturation. The first aim is to investigate the role of the Rb gene family during cellular reprogramming leading to the production of induced pluripotent stem cells (iPSCs). The second specific aim focuses on determining the mechanism of action of Rb family members in the reprogramming process. Reviewers believed that this proposal was significant and addresses a major unsolved problem in stem cell biology. Reviewer enthusiasm was heightened by their expectation that the project will yield novel insights into the oncogenic potential of stem cells, since mechanisms associated with the generation of iPSCs share prominent similarities with oncogenic activation and epigenetic changes that occur during the process of tumorigenesis. The project is concerned with a novel area of investigation, and a key strength of the proposal is its focus on molecular and cellular mechanisms that underlie the role of Rb in reprogramming. Reviewers were highly enthusiastic about the proposal’s experimental design and feasibility. The experiments are carefully designed to yield meaningful results. Reviewers felt that the proposed experiments would reveal the relationship between Rb and the known reprogramming factors and should allow for the identification of other relevant genes controlled by Rb. The thorough description of the experimental plan, logical project rationale, and appropriate and achievable goals were major strengths of the application. There was some concern that a few aspects of the project, such as the high throughput sequencing to directly determine the targets of Rb and analysis of posttranslational effects of Rb, were overly ambitious and unnecessary to achieve the central goals of the study. However, the proposal is supported by some compelling preliminary data, and reviewers expressed high expectations for the project’s success. The PI is a young investigator with excellent training who has made substantial and significant contributions to an understanding of Rb gene family. The PI’s commitment of a high percent effort to the proposed research heightens prospects for the project’s success. The research team possesses the appropriate experience to carryout the proposed study. Additionally, the research environment is outstanding. In summary, the overarching goal of this proposal is to understand mechanisms controlling the balance between stem cell pluripotency, self-renewal, and tumorigenesis and to elucidate the role of the RB gene family in coordinating these processes. This proposal presents a detailed experimental plan with strong emphasis on mechanism. The project is innovative and focused on an important problem in stem cell biology.