Characterization of OS -9, a novel Myc -interacting protein
Abstract
The Myc oncoprotein is a member of the basic helix-loop-helix leucine zipper (bHLH/LZ) family of nuclear transcription factors. Myc heterodimerizes with the bHLH/LZ protein Max to form a DNA binding complex that positively regulates target gene transcription. The amino terminus of Myc encodes a transcription activation domain (TAD) containing two highly conserved regions, MHRI and MHRII. Most of the Myc-induced biological responses, including cellular transformation and apoptosis, require an intact MHRII domain, implying that protein-protein interactions occurring through MHRII mediate these effects. To identify cellular proteins that interact with MHRII, a yeast two-hybrid screen was performed. As a result of that screen, a cDNA was isolated that encodes OS-9, the product of a gene previously identified as amplified in a human osteosarcoma cell line. The specificity of the OS-9/Myc interaction was established using in vitro binding assays as well as in vivo co-immunoprecipitation. Functional assays reveal that OS-9 inhibits the ability of Myc to transcriptionally activate reporter gene expression. In addition, ectopic expression of OS-9 in Rat1a fibroblasts inhibits the ability of a MycER protein to induce cell proliferation and growth, but not apoptosis. Interestingly, OS-9 and Myc can be co-localized in the cytoplasm of some cell types, leading to speculation that OS-9 dependent inhibition of Myc function is achieved through the sequestration of Myc in the cytoplasm.
Degree
Ph.D.
Advisors
Taparowsky, Purdue University.
Subject Area
Molecular biology
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