"Inhibition of tumorigenicity by the 5'-untranslated RNA of the human c-myc P0 transcript".

Scott W. Blume ^{a, b, c, @}, Donald M. Miller ^d, Vincenzo Guarcello ^e, Kedar Shrestha ^f, Zheng Meng ^b, Richard
C. Snyder ^a, William E. Grizzle ^{c, g}, J. Michael Ruppert ^{a, b, c}, G. Larry Gartland ^{c, h}, Cecil R. Stockard ^g, David E. Jones, Jr. ⁱ and Peter D. Emanuel ^{a, b, c}

^a Department of Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, USA
^b Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham, Birmingham, AL 35294, USA
^c Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL 35294, USA
^d Departments of Medicine and Pharmacology and Toxicology, James Graham Brown Cancer Center, University of Louisville, KY 40202, USA
^e Department of Pharmacology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
^f Department of Anesthesiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
^g Department of Pathology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
^h Department of Microbiology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
ⁱ H. Lee Moffitt Cancer Center, University of South Florida, Tampa, FL 33612, USA

^@ Corresponding author. 1824 6th Avenue South, Tumor Institute Room 508, Birmingham, AL 35294-3300.
Fax: +1-205-975-6911;  E-mail:  scott.blume@ccc.uab.edu

Activity of the independently regulated human c-myc P0 promoter has been associated with the undifferentiated status of leukemia cells as well as the hormone-independent proliferation of breast cancer cells. The P0 transcript is distinguished from the predominant P1 and P2 c-myc mRNAs by an ~639-nucleotide extension of the 5'-untranslated region. We hypothesized that this complex 5'-untranslated RNA sequence unique to the P0 transcript may contribute significantly to the composite regulation of the c-myc locus and that enforced intracellular synthesis of the isolated P0 5'-UTR, out of its native sequence context, might amplify or dominantly interfere with its normal regulatory function. Human tumor (HeLa) cells in which the isolated P0 5'-UTR was ectopically expressed displayed a dramatic decrease in anchorage-independent proliferation. Furthermore, P0 5'-UTR-expressing HeLa cells failed to form tumors when inoculated into SCID mice. This loss of tumorigenicity was associated with increases in levels of the c-Myc1 (p67) and c-Myc2 (p64) proteins and a 3- to 5-fold elevation of spontaneous apoptotic index. These results demonstrate that an isolated 5'-untranslated RNA sequence can be attributed potent in trans gene-regulatory and phenotype-altering capabilities and that extrinsic alterations in c-myc regulation can be utilized to reestablish the natural proapoptotic (tumor suppressor) activities associated with this protooncogene. 

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