Neoplastic development: paradoxical relation between impaired cell growth at low population density and excessive growth at high density.

Abstract

The role of heritable, population-wide cell damage in neoplastic development was studied in the 28 L subline of NIH 3T3 cells. These cells differ from the 173c subline used previously for such studies in their lower frequency of "spontaneous" transformation at high population density and their greater capacity to produce large, dense transformed foci. Three cultures of the 28 L subline of NIH 3T3 cells were held under the constraint ofconfluence for 5 wk (5 wk 10 assay) and then assayed twice in succession (20 and 3°assays) for transformed foci and saturation density. After the 20 assay, the cells were also passaged at low density to determine their exponential growth rates and cloned to determine the size and morphological features of the colonies. Concurrent measurements were made in each case with control cells that had been kept only in frequent low-density passages and cells that had been kept at confluence for only 2 wk (2 wk 10). Two of the three cultures transferred from the 20 assay of the 5 wk 1°cultures produced light transformed foci, and the third produced dense foci. The light focusforming cultures grew to twice the control saturation density in their 20 assay and 6-8 times the control density in the 30 assay; saturation densities for the dense focis formers were about 10 times the control values in both assays. All three of the cultures transferred from the 20 assay ofi the 5 wk 10 cultures multiplied at lower rates than controls at low densities, but the dense focus formers multiplied faster than the light focus formers. The reduced rates of multiplication of the light focus formers persisted for >50 generations of exponential multiplication at low densities. Isolated colonies formed from single cells of the light focus formers were of a lower population density thaR, controls; colonies formed by the dense focus formers were slightly denser than the controls but occupied only half the area. A much higher proportion of the colonies from the 5 wk 10 cultures than the controls consisted of giant cells or mixtures of giant and normal-appearing cells, The'results reinforce the previous conclusion that the early increases in saturation density and light fo&us formation are associated with, and perhaps caused by, heritable, populationwide damage to cells that is essentially epigenetic in nature.

SSeCKS, a Major Protein Kinase C Substrate with Tumor Suppressor Activity, Regulates G1→S Progression by Controlling the Expression and Cellular Compartmentalization of Cyclin D

“…Our data also suggest that SSeCKS ensures contact-inhibited growth through a secondary, fail-safe function, that being an ability to scaffold residual cyclin D protein in the cytoplasm. In agreement with this, several studies have shown that continuous plating of untransformed chick embryo fibroblasts at high densities increases the frequencies of spontaneous oncogenic transformation compared to cells plated at low densities (13,14,50).…”

Quantitative aspects of the selective killing of transformed cells by methotrexate in the presence of leucovorin

“…We have noted previously that transformed cells multiply more slowly at low population density in 10% CS than their nontransformed counterparts (33,34). We have noted previously that transformed cells multiply more slowly at low population density in 10% CS than their nontransformed counterparts (33,34).…”

“…The impairment of growth, most apparent at low density, is a common accompaniment of transformation and apparently reflects genetic damage to the cells (3)(4)(5)31,33,34,37). By contrast, the transformed cells multiplied at the same rate as they did at low population density, although exhibiting a shorter lag period.…”

Germline versus somatic mutations of theAPC gene: Evidence for mechanistic differences

“…It would be of particular interest to determine whether the expression of these genes is altered by radically different environmental conditions such as would be encountered in cells of the colonic epithelium. Such a situation might provide an explanation for the observed variations in transformation efficiency of cells in culture when subjected to varying conditions of cell density and serum concentration (Rubin et al, 1992(Rubin et al, , 1995, as well as the effects described here.…”