PHASE-TRANSITIONS IN THE GROWTH OF C3H 10T1 2 CELLS/

In systems used to express transformation using focus formation as the end point, nontransformed cells generally express a down-regulation o f cell growth and division made evident by the formation of a monolaye r of cells that completely covers the growth surface. In C3H 10T1/2 ce lls, down-regulation is thought to be progressively effected principal ly by cell-to-cell communication via gap junctions. Starting with a sp arse population in asynchronous growth-e.g. containing cells in all ph ases of the growth cycle-as the area density increases, cells are prog ressively lost from the distribution in the order M phase, G(2) phase, S phase and G(1) phase, leading to the accumulation of viable cells o ut of cycle in so-called G(0) phase. We have measured the progressive phase transitions as a function of inoculum size and time. The influen ce of a promoter and an antipromoter was also examined as well as the expression of the cyclin/cyclin-dependent kinase inhibitors p21(Waf1/C ip1) and p27(Kip1) as the cells grew into confluence. Using cells sync hronized in mitosis, we found that with increasing cell density the ex pression of p27 increased and concomitantly p21 decreased. (C) 1998 by Radiation Research Society.