Tumorigenesis requires cells to bypass or escape two discrete and distinctive anti-proliferative barriers: replicative senescence and crisis. Senescence is a permanent cell cycle arrest, activated as a primary response to telomere deprotection and involves stimulation of the tumor suppressor pathways p53-p21WAF1 and/or p16INK4A- Rb. Disruption of cell-cycle checkpoints renders cells capable of bypassing senescence and continuing proliferation, while telomeres shorten further. Eventually such cells initiate a terminal response called replicative crisis, during which critically short telomeres become subject to end-to-end fusions, resulting in massive cell death. On rare occasion, a small group of cells will emerge spontaneously from crisis and evolve towards malignancy, yet the mechanisms underlying cell death in crisis and crisis escape are not defined. Dr. Joe Nassour has recently discovered an unrecognized function for macroautophagy (hereafter autophagy) in the elimination of cells during crisis. Autophagy is therefore an essential component of the crisis response required for the removal of cells at risk for malignant transformation. This suggests that autophagy defects can be the molecular basis for tumorigenesis. In his Pathway to Independence Award (K99/R00) proposal, Dr. Nassour, together with his Mentor Dr. Jan Karlseder, and his Co-Mentors Dr. Reuben Shaw, Dr. Martin Hetzer, and Dr. Peter Adams, designed a dedicated training plan and proposed a research project that sets out to dissect the molecular basis of mammalian autophagy and its potential therapeutic role in the earliest stages of human cancer. In particular, Dr. Nassour will focus on deciphering the mechanism of autophagy-dependent cell death in crisis (Aim 1), elucidating the interplay between autophagy and genome stability (Aim 2), and evaluating the role of autophagy in neoplastic transformation through crisis escape (Aim 3). The in vivo relevance of Aim 3 will be examined by employing knockout and transgenic mouse models susceptible to telomere dysfunction-driven carcinogenesis. The occurrence of cellular crisis in tissues and the impact of autophagy on tumor incidence will be examined. This research will provide new insights into the function of autophagy in cancer biology, and should provide a rationale for developing autophagy modulation approaches to ameliorate the efficacy of cancer therapy. Dr. Nassour?s training plan will provide all the necessary professional development to direct an independent laboratory using next-generation sequencing (NGS)-based ?omics? approaches and transgenic mouse models to define the mechanisms and function of autophagy in cancer. Training modules in this award include: Computational analysis and bioinformatics for NGS data, methods for handling and restraint in the mouse, transgenic mouse technology, and mentorship skills such as teaching and grant writing; which will all be necessary for the success following the transition to independence.
Proposed studies will characterize the autophagy-dependent mechanism(s) that regulate a cell's ability to escape from replicative crisis and initiate a tumor. This research will increase our understanding about the molecular basis of autophagy and its implication in cell death, genome stability, and early stages of malignant transformation. In addition to these fundamental advances, this project has translational potential because it will provide new insights into the roles of autophagy in cancer biology and will enhance the efficacy of existing autophagy manipulation methods.