Each year, well over 150,000 US cancer deaths is linked to deregulated MYC oncogene, which encodes the Myc transcription factor that regulates about 10% of genes. Our genome-wide chromatin immunoprecipitation study of Myc binding sites in neoplastic human P493 B cell model with inducible MYC and our recent genome wide measure of nuclear run-on rates reveal a new link between MYC and E2F, regulation of nucleotide metabolism and cell cycle transit. Among many metabolic pathways that could be influenced by MYC, glucose and nucleotide metabolic gene sets are over-represented among MYC target genes. In addition, we identified a novel enzyme activity for Rcl, encoded by a Myc target gene that we cloned a decade ago. This novel activity converts deoxynucleotide monophosphate to the respective base and deoxyribose, which could stimulate angiogenesis or used as an energy source. These findings suggest that Myc influences nucleotide metabolism for nucleic acid synthesis as well as potentially connecting nucleotide biosynthesis with energy metabolism. We propose studies that will delineate the role of Myc in regulating both pyrimidine and purine biosynthesis as well as RCL. We will use small molecular inhibitors of these pathways and Rcl to determine the influence of loss-of-function on tumorigenesis. We also uncovered a connection between MYC and a potent previously unsuspected modifier, the hypoxia inducible factor 1 (HIF-1), of MYC tumorigenic function in vivo. HIF-1 is a potent modulator of glucose metabolism, which is also regulated by Myc. We previously hypothesized that anti- oxidants, such as N-acetylcysteine or vitamin C, decrease tumorigenesis by interfering with genomic instability by squelching reactive oxygen specifes induced by Myc. Our data not only indicate that tumorigenesis of the Myc-dependent P493 cells is not associated with chromosomal instability, but they also indicate that anti-oxidants inhibit tumorigenesis through enhancing the degradation of HIF-1. These observations reveal the interplay between Myc and E2F in influencing the regulation of nucleotide metabolism, and Myc and HIF-1 in influencing energy metabolism and angiogenesis. To reach our goal of understanding the link between Myc, nucleotide metabolism, energy regulation and angiogenesis, we set the following specific aims:
Aim 1. To determine the role of Myc and E2F in regulating genes involved in nucleotide metabolism and RCL. To determine the apoptotic and biological consequences of inhibiting Rcl and critical enzymes and factors in these pathways and how these perturbations influence energy metabolism.
Aim 2. To determine the role of HIF-1 as a modifier of MYC function and the anti-tumorigenic mechanism(s) of N-acetylcysteine and vitamin C in models of Myc-mediated tumorigenesis.
The MYC cancer gene is associated with over 150,000 US cancer deaths each year, and we have previously linked MYC to altered tumor energy metabolism and have provided novel therapeutic insights. In this application, we plan to connect MYC with the regulation of DNA synthesis that is essential for cancer development. We have shown that the hypoxia inducible factor, HIF that is required for tumor to recruit new blood vessels and to adapt to low oxygen tension, is essential for the cancer-inducing ability of MYC and plan to determine how the antioxidants, vitamin C and N- acetylcysteine, decrease the function of HIF to inhibit MYC-mediated cancer growth.
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