Control of cell growth by c-Myc in the absence of cell division

The c-Myc protein (Myc) is a transcription factor, and deregulated expressi on of the c-myc gene (myc) is frequently found in tumours, In Burkitt's lym phoma (BL), myc is transcriptionally activated by chromosomal translocation , We have used a B-cell line called P493-6 that carries a conditional myc a llele to elucidate the role of Myc in the proliferation of BL cells. Regula tion of proliferation involves the coordination of cell growth (accumulatio n of cell mass) and cell division [1-3]. Here, we show that division of P49 3-6 cells was strictly dependent on the expression of the conditional myc a llele and the presence of foetal calf serum (FCS). More importantly, cell g rowth was regulated by Myc without FCS: Myc alone induced an increase in ce ll size and positively regulated protein synthesis. An increase in protein synthesis is thought to be one of the causes of cell mass increase. Further more, Myc stimulated metabolic activities, as indicated by the acidificatio n of culture medium and the activation of mitochondrial enzymes. Our result s confirm the model that Myc is involved in the regulation of cell growth [ 4] and provide, for the first time, direct evidence that Myc induces cell g rowth, that is, an increase in cell size, uncoupled from cell division. (C) 1999 Elsevier Science Ltd. All rights reserved.