Regulation of cell cycle duration by c-myc levels

摘要: Early passage murine fibroblasts infected with retroviral vectors carrying human c-myc 'minigenes' express high levels of and have a dramatically shortened G1-phase the cell cycle. Cells viruses where is expressed from viral LTR (MSN-4 virus) more protein than cells SV40 early promoter (NSM-7 virus). Populations were titre viruses, selected for drug-resistance, pulse labelled bromodeoxyuridine (BrdUrd) chased in BrdUrd free media. This allows accurate, simultaneous, measurement rate exit unlabelled G1 progression BrdUrd-labelled through S-phase. The length populations MSN-4 virus 4.65 h, reduction nearly 30% compared to 6.50 h seen VSN-2 control virus. NSM-7 show an intermediate phenotype 5.25 h. lengths S-phase (4.50 4.75 h) G2 + M phases (2.75 not significantly altered by exogenous expression. When chases are performed growth-factor media, non-infected extended approximately 2 continue cycle rapidly uninfected cells. Growth factor-deprived cells, restimulated serum, similar alterations kinetics. expressing c-myc, enter 4 earlier, but less synchronously, sustain subsequent rounds DNA synthesis, while do not. However, activated genes nearly-normal morphologies tumourgenic syngenic mice. These results demonstrate that limiting events G1, varies proportionally level