The c-Myc transcription factor is a potent inducer of cell proliferation and transformation, and elevated levels of c-Myc protein are observed in most human tumors. However, c-Myc overexpression also induces apoptosis, which limits c-Myc's tumorigenic potential. There are two conserved phosphorylation sites, Threonine 58 (T58) and Serine 62 (S62) that differentially regulate c-Myc protein stability in response to mitogenic stimulation, where S62 phosphorylation increases c-Myc stability, while T58 phosphorylation decreases c-Myc stability. Recent evidence suggests that phosphorylation at these sites also regulates c-Myc's apoptotic versus tumorigenic potential. Specifically, low phosphorylation at T58 and high phosphorylation at S62, which is the signature for more stable c-Myc, appears to suppress c-Myc's apoptotic activity and enhance its proliferative properties. Recent results indicate that lower T58 and higher S62 phosphorylation occurs in some tested human cancer cell lines with aberrantly stabilized c-Myc protein due to deregulation of the pathway that controls c-Myc degradation. Moreover, similarly altered phosphorylation of c-Myc has been detected in primary breast cancer samples. This suggests that cancer cells may contain a more oncogenic form of c-Myc. The objective of this grant is to examine the role of phosphorylation at T58 and S62 in controlling c-Myc's apoptotic versus proliferative activity, and whether this mechanism contributes to c-Myc's transforming activity in human cancer. The following specific aims will be pursued: 1) Examine the activity of c-Myc T58 and S62 phosphorylation mutants in vivo using a unique mouse model;2) Investigate mechanisms that could underlie the different phenotypic responses to expression of c-Myc T58 and S62 phosphorylation mutants;and 3) Examine the phosphorylation status of c-Myc at T58 and S62 in human cancer cells and whether manipulation of c-MycWT phosphorylation can affect its oncogenic potential.
These aims i nvolve the study of novel inducible c-myc knock-in mice that express either wild-type c-Myc or c-Myc T58 or S62 phosphorylation mutants in specific tissues, in vitro and in vivo assays to investigate the underlying mechanisms of how these sites affect c-Myc activity, and an analysis of human cancer to explore the relevance of altered phosphorylation at these sites and whether cell transformation can be affected by non-genetic manipulation of c-Myc T58 and S62 phosphorylation. This research has important therapeutic implications, since targeting the pathway that regulates T58 and S62 phosphorylation could potentially affect both c-Myc expression levels and tumorigenic activity.
The proposed research focuses on understanding how the oncogenic potential of the transcription factor c-Myc is affected by its phosphorylation status at two highly conserved sites, which also regulate its protein stability. Importantly, elevated expression of c-Myc is widely observed in many different human tumors and therefore understanding mechanisms that increase or decrease c-Myc's oncogenic potential are critical to the development of future therapies targeting this potent oncoprotein.
|Janghorban, Mahnaz; Farrell, Amy S; Allen-Petersen, Brittany L et al. (2014) Targeting c-MYC by antagonizing PP2A inhibitors in breast cancer. Proc Natl Acad Sci U S A 111:9157-62|
|Farrell, Amy S; Allen-Petersen, Brittany; Daniel, Colin J et al. (2014) Targeting inhibitors of the tumor suppressor PP2A for the treatment of pancreatic cancer. Mol Cancer Res 12:924-39|
|Juan, Joseph; Muraguchi, Teruyuki; Iezza, Gioia et al. (2014) Diminished WNT -> ?-catenin -> c-MYC signaling is a barrier for malignant progression of BRAFV600E-induced lung tumors. Genes Dev 28:561-75|
|Daniel, Colin J; Zhang, Xiaoli; Sears, Rosalie C (2013) Detection of c-Myc protein-protein interactions and phosphorylation status by immunoprecipitation. Methods Mol Biol 1012:65-76|
|Farrell, Amy S; Pelz, Carl; Wang, Xiaoyan et al. (2013) Pin1 regulates the dynamics of c-Myc DNA binding to facilitate target gene regulation and oncogenesis. Mol Cell Biol 33:2930-49|
|Wang, Zhiping; Liu, Yuangang; Takahashi, Maho et al. (2013) N terminus of ASPP2 binds to Ras and enhances Ras/Raf/MEK/ERK activation to promote oncogene-induced senescence. Proc Natl Acad Sci U S A 110:312-7|
|Mannava, S; Omilian, A R; Wawrzyniak, J A et al. (2012) PP2A-B56? controls oncogene-induced senescence in normal and tumor human melanocytic cells. Oncogene 31:1484-92|
|Zhang, Xiaoli; Farrell, Amy S; Daniel, Colin J et al. (2012) Mechanistic insight into Myc stabilization in breast cancer involving aberrant Axin1 expression. Proc Natl Acad Sci U S A 109:2790-5|
|Wang, Xiaoyan; Cunningham, Melissa; Zhang, Xiaoli et al. (2011) Phosphorylation regulates c-Myc's oncogenic activity in the mammary gland. Cancer Res 71:925-36|