Analysis of the v-Myc transcription activation domain and its interaction with OS-9, a novel Myc-associating factor
Abstract
Oncoproteins of the Myc family are important regulators of cellular proliferation, differentiation, transformation, and apoptosis. Myc is a basic helix-loop-helix/leucine zipper transcription factor that contains an amino terminal transcription activation domain, or TAD. Overwhelming evidence suggests the TAD of Myc is responsible for mediating all of Myc's functions in vivo. In an attempt to more clearly define regions of the amino terminus important to Myc activity, deletion mutagenesis of the v-Myc TAD was performed. Examination of the truncated Myc proteins by reporter gene assays identified a region within the v-Myc amino terminus that acts as a negative regulatory domain. Specifically when this region of 25 amino acids is removed from the v-Myc protein, both the transactivating and transforming properties of v-Myc are enhanced. Besides the deletion mutagenesis performed on the v-Myc TAD, a yeast two-hybrid screen was performed using a human B cell cDNA library and a highly conserved domain of the v-Myc TAD called Myc homology region II, or MHR II. Analysis of the 22 positive clones obtained indicated that 8 represented independent overlapping isolates of the cDNA encoding the OS-9 protein. In vitro binding experiments demonstrate OS-9 specifically interacts with regions of the v-Myc TAD that contain MHR II. To determine the functional consequences of the Myc/OS-9 interaction, cellular transformation assays were performed; however, overexpression of OS-9 does not influence Myc-mediated transformation. Interestingly, co-expression of OS-9 dramatically inhibits transactivation by Myc and enhances transcriptional repression by Myc, depending upon the context of the Myc reporter used. More importantly, expression of OS-9 slows the growth of cells stimulated to proliferate by v-Myc overexpression. These data indicate that OS-9 is a novel modulator of v-Myc transcriptional activity, and that this modulation has important consequences to the growth of cells.
Degree
Ph.D.
Advisors
Taparowsky, Purdue University.
Subject Area
Molecular biology|Oncology
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