The Type I Insulin-like Growth Factor Receptor (IGF-IR) clearly plays a critical role in breast tumorigenesis through its capacity to facilitate malignant transformation, promote cell proliferation, and protect malignant cells from apoptosis. The human IGF-IR mRNA contains an extraordinarily long (1,038 nucleotides) leader sequence (5'-untranslated RNA, 5'-UTR), which functions as the equivalent of a """"""""promoter"""""""" at the RNA level. We have identified three regulatory proteins (HuR, TIAR, hnRNP C) that bind in a sequence-specific manner to the IGF-IR 5'-UTR and appear to control the efficiency with which the IGF1R mRNA is translated into protein. We hypothesize that alterations in the dynamic interactions between these RNA-binding proteins and the 5'-untranslated sequence of the IGF-IR transcript may be responsible for IGF-IR overexpression in a proportion of human breast tumors, and ultimately contribute to the molecular pathogenesis of this disease. Indeed we have found a marked increase in IGF-IR translational efficiency in association with significant alterations in the activities of these RNA-binding proteins in the human breast carcinoma cell line T47D, which overexpresses IGF-IR. In addition, we propose to test the potential therapeutic utility of the isolated IGF-IR 5'-untranslated RNA, functioning as a dominant negative regulatory RNA, to specifically counteract IGF-IR overexpression and reverse the associated adverse phenotypic consequences in human breast cancer cells. We have established that such a strategy can be used to induce dramatic, favorable phenotypic alterations, including mitotic cell death and loss of tumorigenicity.
The Specific Aims are: 1. Establish the function of the RNA-binding proteins TIAR and hnRNP C in the regulation of IGFIR expression at the translational level. 2. Assay primary human breast tumor specimens for the activities of sequence, specific translation-regulatory proteins binding the 5'-untranslated region of the human IGFIR transcript (including HuR, TIAR, and hnRNP C), and correlate changes in activities of these RNA-binding proteins with IGF-IR overexpression and the malignant phenotype. 3. Ectopically express the isolated IGFIR 5'-untranslated RNA sequence in human breast cancer cells, assess the potential of this non-coding RNA sequence to modulate IGF1R expression, and consequently limit proliferative capacity, enhance apoptotic susceptibility, and reverse tumorigenicity of human breast cancer cells.
|Vaklavas, Christos; Grizzle, William E; Choi, Hyoungsoo et al. (2016) IRES inhibition induces terminal differentiation and synchronized death in triple-negative breast cancer and glioblastoma cells. Tumour Biol 37:13247-13264|
|Vaklavas, Christos; Meng, Zheng; Choi, Hyoungsoo et al. (2015) Small molecule inhibitors of IRES-mediated translation. Cancer Biol Ther 16:1471-85|
|Meng, Zheng; Jackson, Nateka L; Shcherbakov, Oleg D et al. (2010) The human IGF1R IRES likely operates through a Shine-Dalgarno-like interaction with the G961 loop (E-site) of the 18S rRNA and is kinetically modulated by a naturally polymorphic polyU loop. J Cell Biochem 110:531-44|
|Blume, Scott W; Jackson, Nateka L; Frost, Andra R et al. (2010) Northwestern profiling of potential translation-regulatory proteins in human breast epithelial cells and malignant breast tissues: evidence for pathological activation of the IGF1R IRES. Exp Mol Pathol 88:341-52|
|Choi, Hyoungsoo; Jackson, Nateka L; Shaw, Denise R et al. (2008) mrtl-A translation/localization regulatory protein encoded within the human c-myc locus and distributed throughout the endoplasmic and nucleoplasmic reticular network. J Cell Biochem 105:1092-108|
|Meng, Zheng; Jackson, Nateka L; Choi, Hyoungsoo et al. (2008) Alterations in RNA-binding activities of IRES-regulatory proteins as a mechanism for physiological variability and pathological dysregulation of IGF-IR translational control in human breast tumor cells. J Cell Physiol 217:172-83|
|Meng, Zheng; King, Peter H; Nabors, L Burt et al. (2005) The ELAV RNA-stability factor HuR binds the 5'-untranslated region of the human IGF-IR transcript and differentially represses cap-dependent and IRES-mediated translation. Nucleic Acids Res 33:2962-79|