TRANSLATIONAL CONTROL OF ONCOPROTEIN MDM2 SYNTHESIS

Summary

Principal Investigator: D R Morris
Abstract: Oncoprotein MDM2 is a component of a negative feedback loop that regulates the activity and cellular level of tumor suppressor p53. The synthesis of MDM2 is regulated at the translational level in resting fibroblasts that are activated to reenter the cell cycle. In one class of soft tissue tumors, synthesis of MDM2 protein is enhanced by one to two orders of magnitude without a corresponding increase in mRNA level. In all cell types examined, there are two forms of mdm2 mRNA. The long form (L-mdm2) contains a 287-nucleotide 5' leader, with two upstream open reading frames (uORFs), derived from exon 1 and the short form (S-mdm2) has a 64-nucleotide leader arising from exon 2. L-mdm2 is inefficiently loaded with ribosomes in normal fibroblasts, HeLa cells and choriocarcinoma cells. The L-mdm2 leader confers inefficient ribosome loading on a reporter gene and the two uORFs cooperate synergistically to suppress translation. In the choriocarcinoma cell line, in which MDM2 expression is translationally derepressed, the synergistic interaction between the uORFs in the L-mdm2 leader is lost. The S-mdm2 mRNA is well loaded with ribosomes in the choriocarcinoma cells, but is poorly translated in normal fibroblasts and HeLa cells. Fusion constructs containing the S-mdm2 leader are well translated in all cell types, suggesting that the translational suppression in normal cells requires another element in part of the mRNA other than the 5' leader. This application proposes a series of experiments designed to define the mechanisms of translational control of the mdm2 gene in normal and neoplastic cells. The synergistic interaction between the two uORFs in L-mdm2 is of particular interest, first because it is lost in tumor cells that overexpress MDM2 protein and, second, because there is no mammalian model that is readily accessible for experimental study of the mechanism of regulation by multiple, interacting uORFs. By analogy to the regulation by multiple uORFs in the yeast GCN4 gene, the possible involvement of phosphorylation of eIF-alpha in regulation of MDM2 translation will be tested. The sequences in the S-mdm2 mRNA that are responsible for the differences in its translation between normal and tumor cells will also be defined.
Funding Period: 1999-07-01 - 2005-04-30
more information: NIH RePORT

Top Publications

  1. pmc The undertranslated transcriptome reveals widespread translational silencing by alternative 5' transcript leaders
    G Lynn Law
    Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
    Genome Biol 6:R111. 2005
  2. ncbi Silencing the transcriptome's dark matter: mechanisms for suppressing translation of intergenic transcripts
    Kellie S Bickel
    Department of Biochemistry, University of Washington, Box 357350, Seattle, 98133, USA
    Mol Cell 22:309-16. 2006
  3. pmc Role of the transcription activator Ste12p as a repressor of PRY3 expression
    Kellie S Bickel
    Department of Biochemistry, University of Washington, Box 357350, Seattle, WA 98195, USA
    Mol Cell Biol 26:7901-12. 2006

Scientific Experts

Detail Information

Publications3

  1. pmc The undertranslated transcriptome reveals widespread translational silencing by alternative 5' transcript leaders
    G Lynn Law
    Department of Biochemistry, University of Washington, Seattle, WA 98195, USA
    Genome Biol 6:R111. 2005
    ..Unexpectedly, a high frequency of these transcripts showed the appearance of altered 5' leaders that coincide with increased ribosome loading...
  2. ncbi Silencing the transcriptome's dark matter: mechanisms for suppressing translation of intergenic transcripts
    Kellie S Bickel
    Department of Biochemistry, University of Washington, Box 357350, Seattle, 98133, USA
    Mol Cell 22:309-16. 2006
    ..A variety of mechanisms exist to prevent adventitious production of proteins from these transcripts, ranging from degradation within the nucleus to translational silencing in the cytosol...
  3. pmc Role of the transcription activator Ste12p as a repressor of PRY3 expression
    Kellie S Bickel
    Department of Biochemistry, University of Washington, Box 357350, Seattle, WA 98195, USA
    Mol Cell Biol 26:7901-12. 2006
    ..PRY3 regulation provides a model for the coordination of both inductive and repressive activities within a regulatory network...