SERUM DEPRIVATION RESPONSE GENE IS INDUCED BY SERUM STARVATION BUT NOT BY CONTACT INHIBITION

The relationship between quiescence induced by serum deprivation and t hat induced by high cell density (contact inhibition) is still unclear . Here, we describe a gene, named sdr (serum deprivation response), wh ose mRNA level is highly induced in serum starved but not in density d ependent growth arrested NIH3T3 cells. sdr induction seems to be coupl ed 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 not iced at later times after fetal calf serum stimulation, this is not th e case for epidermal growth factor, for which the sdr mRNA level remai ns down-regulated. The data presented here point to the possibility th at the density dependent growth arrest state cannot be simply explaine d 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.