c-Myc enhances protein synthesis and cell size during B lymphocyte development

Members of the myc family of nuclear protooncogenes play roles in cell prol iferation, differentiation, and apoptosis, Moreover, inappropriate expressi on of c-myc genes contributes to the development of many types of cancers, including B cell lymphomas in humans. Although Myc proteins have been shown to function as transcription factors, their immediate effects on the cell have not been well defined. Here we have utilized a murine model of lymphom agenesis (E mu-myc mice) to show that constitutive expression of a c-myc tr ansgene under control of the Ig heavy-chain enhancer (E mu) results in an i ncrease in cell size of normal pretransformed B lymphocytes at all stages o f B cell development. Furthermore, we show that c-Myc-induced growth occurs independently of cell cycle phase and correlates with an increase in prote in synthesis. These results suggest that Myc may normally function by coord inating expression of growth-related genes in response to mitogenic signals . Deregulated c-myc expression may predispose to cancer by enhancing cell g rowth to levels required for unrestrained cell division.