Serum deprivation response gene is induced by serum starvation but not by contact inhibition.

The relationship between quiescence induced by serum deprivation and that induced by high cell density (contact inhibition) is still unclear. Here, we describe a gene, named sdr (serum deprivation response), whose mRNA level is highly induced in serum starved but not in density dependent growth arrested NIH3T3 cells. sdr induction seems to be coupled to growth arrest since it does not become apparent when transformed NIH3T3 cells are cultured in low serum. The expression of sdr is down-regulated within 6 h after the addition of serum or epidermal growth factor to serum starved cells. Although a transient reinduction is noticed at later times after fetal calf serum stimulation, this is not the case for epidermal growth factor, for which the sdr mRNA level remains down-regulated. The data presented here point to the possibility that the density dependent growth arrest state cannot be simply explained by local growth factor depletion, as occurs in overcrowded cultures, but it could be the consequence of a more complex pathway mediated by cellular interactions.