Myc Mediated Transcriptional Modulation Sanjay J. Chandriani a Dissertation Presented to the Faculty of Princeton University in Candidacy for the Degree of Doctor of Philosophy Recommended for Acceptance by the Department of Molecular Biology

Deregulated Myc expression can lead to profound physiological changes in cells, including increased cell proliferation, oncogenic transformation, apoptosis and inhibition of differentiation. Myc is a transcription factor that can both stimulate and inhibit transcription and is believed to affect the physiological changes by coordinate regulation of many Myc responsive genes. To define the global transcriptional response to Myc, we undertook an expression microarray analysis of deregulated Myc expression in primary human fibroblast cells. In this analysis, we identified a core Myc gene expression signature that could be used to analyze the expression profiling datasets of human cancers. With this approach, we were able to identify malignant tissue samples that display the Myc gene expression profile. For example, basal-like breast carcinomas often displayed the Myc signature. One hallmark of transformed cells in vitro is a reduced dependence on serum for cell survival and proliferation. To determine if deregulated Myc expression underlies this reduced dependence on serum by regulating serum response genes, we were able to interrogate our data for those genes that had previously been defined in the core serum response (CSR). Many CSR genes responded to both Myc and serum similarly. However, the complete CSR was not recapitulated by Myc overexpression. Using a genetic approach to identify proteins that can complement the slow growth phenotype in cells lacking Myc expression, we were unable to identify a single gene product (other than Myc family members) that could completely complement the phenotype. One gene product, mitochondrial serine hydroxymethyltransferase (mSHMT), was identified in the genetic screen to partially complement the growth phenotype and was subsequently characterized as a direct Myc target gene. This enzyme catalyzes reactions that provide a major source of the one carbon unit that is required for many metabolic processes. Myc can stimulate the expression of a gene that is silent in most somatic cells. This gene, hTERT, is the catalytic subunit of telomerase and has been found to be expressed in most malignant cells. We demonstrated a required role for the recruitment of TRRAP and the associated histone acetyltransferase activity for Myc mediated transactivation of the hTERT gene.