Species Specificity in Growth Regulatory Effects of Cellular Interaction

Abstract

SURFACE (monolayer) cultures of human diploid cells show a marked decrease in the rate of synthesis of DNA, RNA and net protein as the population density of the cultures increases¹, but it has not yet been determined whether growth inhibition occurs because of actual cellular contact, or whether growth inhibitory compounds are released extracellularly to act only at very short range². Heteroploid epithelial human cells, either arising as spontaneous transformants in cultures of normal cells, or cultured from cancerous tissue, were much less susceptible than diploid cells to growth inhibitory effects and attained three to ten-fold greater population densities. Strains of hypodiploid and trisomic human fibroblasts behaved like normal cells in their susceptibility to population density inhibition³.