The protein synthesis machinery is a major target of oncogenic transformation in breast and other epithelial cancers and is a target, for new therapeutics (e.g., rapamycin analogues). However, the topic remains understudied, mRNAs with 5 UTR structural features that repress translation, such as VEGF, FGF-2, HER-2, and Bcl-2, are predicted to require higher levels of 4E (a rate limiting initiation factor) than other mRNAs. This prediction is supported by tests in model systems. Retroviruses have mutated PI3K and AKT into oncogenes that constitutively increase 4E levels, mTOR (target of rapamycin) kinase increases 4E by releasing a repressor protein. Rapamycin inhibition of mTOR reverses the phenotype of PI3K- or AKT-oncogene transformed cells but not others. 4E itself is also an oncogene, is increased in breast and epithelial cancers, and is associated with tumor progression and invasion. Yet the mechanism of the 4E effect is unknown. My laboratory has cloned tumorigenic cell lines expressing a 4E mutant which decreases their colony size in soft agar. Using this and other systems my team will conduct studies to understand the mechanism of how the quantity of 4E modifies the cancer cell phenotype. I hypothesize that: a) expressing mutant 4E that alters the phenotype of breast cancer cells impairs initiation of translation for VEGF, HER-2, Bcl-2, FGF-2, hypoxia inducible factor (HIF-lalpha) and COX-2 mRNAs; and b) increasing 4E in human mammary epithelial cells (HMECs) stimulates initiation of translation for these mRNAs.
Specific Aims are: 1) to test if these mRNAs are translationally repressed in breast cancer cells by expressing a 4E mutant; 2) to test if these mRNAs are translationally activated by increasing wt 4E in HMECs; 3) to test if increased 4E protects these mRNA from degradation; 4) to test the tumorigenic, metastatic, and tissue invasion properties of model breast cancer cell lines expressing an impaired mutant of 4E in mice and correlate these end points with the expression of the mRNAs listed. These studies may identify new strategies in breast cancer therapy or chemoprevention. ? ?
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