Abstract: While cancer is a genetic disease, the cancerous cellular state is associated with multiple epigenetic alterations including aberrant DNA methylation and histone modification patterns. A significant challenge in cancer biology is to elucidate the precise order of epigenetic alterations during tumor initiation and progression and their contributions to the transformed phenotype. To meet this challenge, one requires a model of cellular transformation that is temporally traceable from a normal to a malignant state. Cancer cell lines are not necessarily good models as they have already accumulated hundreds to thousands of genetic and epigenetic alterations. Here I propose to study the oncogenic transformation of normal human cells by viral oncoproteins as a model to determine the precise epigenetic reprogramming events occurring along the path of neoplastic transformation. Viral oncoproteins such as the Adenovirus small e1a or Papilloma virus E7 have been extraordinarily useful in delineating the central molecular players that regulate cell proliferation such as the retinoblastoma (RB) and p53 tumor suppressors. Our work has recently elucidated a defined global epigenetic reprogramming by one viral oncoprotein, e1a, that forces normal cells to escape quiescence-a hallmark of cancer. Importantly, e1a directly implements a precise and coordinated mechanism of regulation of thousands of host cell genes leading to cellular transformation by interacting and rearranging specific epigenetic modifiers across the whole genome in a time-dependent manner. This provides a powerful model that is amenable to time-series measurements with phenotypically defined endpoints, enabling one to delineate the successive order of epigenetic alterations that contribute to oncogenic transformation. By understanding how e1a orchestrates a specific sequence of epigenetic alterations for cellular transformation, we should learn greatly about the functions and mechanisms of fundamental epigenetic processes in normal biology and human disease, especially cancer. Public Health Relevance: Cancer cells depend on multiple alterations in various molecular pathways to overcome normal defense mechanisms against uncontrolled cell replication. However, how these changes cooperate in time to transform a normal cell to a cancerous one is not very well understood. Certain viruses encode proteins, such as the Adenovirus e1a, that can force a normal cell to overcome its defense mechanism and to replicate-a hallmark of cancer-so that more viral progenies are produced. Because viruses use the cell's own machinery, they have been extraordinarily revealing about processes that must be altered for cancer to arise. We have discovered that the e1a protein displays a highly coordinated program of binding to different sets of host genes at different times after infection. Through such temporally-ordered pattern of binding, the e1a protein rearranges a specific set of gene regulatory enzymes so as to promote cell growth and replication and to repress antiviral responses and molecular pathways that would normally stop the cell from dividing. This is akin to rearranging the furniture in the host's house to serve the guest's sinister purposes. This proposal aims to use e1a-mediated cellular transformation to generate a blueprint for the successive order of events that must occur in a precise manner for cancer to develop. This work may provide fundamental insights into the initial molecular events that lead to cancer development, enabling us to design better therapeutics and/or develop diagnostic and prognostic assays that may aid in personalization of therapy.
| McBrian, Matthew A; Behbahan, Iman Saramipoor; Ferrari, Roberto et al. (2013) Histone acetylation regulates intracellular pH. Mol Cell 49:310-21 |
