Autologous stimulation of YY1 transcription factor expression: role of an insulin-like growth factor.

YY1 is believed to be a constitutive factor, present in all cell types, affecting the transcription of a large number of genes. Experiments in this report demonstrated that YY1 RNA expression in NIH3T3 cells was modulated by media factors, either exogenously added to the media or elaborated by the NIH3T3 cells themselves. This autologous stimulation of YY1 expression was in proportion to the density of cells and was time dependent. Sparsely plated cells lost YY1 RNA expression within hours after being placed under fresh, serum-free media and lost YY1 protein expression by 24 h. Subsequent recurrence of YY1 expression in serum-deprived NIH3T3 cells was significantly decreased by adding monoclonal anti-insulin-like growth factor (IGF)-1 to the media. Radioimmunoassay showed that NIH3T3 cells secreted IGF-1 into the media for up to 72 h after being deprived of serum in the media but did not do so after they became quiescent. In quiescent NIH3T3 cells, YY1 expression was low or absent but was rapidly stimulated by exposure of the quiescent cells to media-containing serum. Exogenous growth factors, either whole serum or purified IGF-1, stimulated YY1 expression equally well. The rapid responses of YY1 expression to growth factor deprivation and replacement suggested the possibility that YY1 may mediate some of the intranuclear responses to autologous stimulation by IGF-1.