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 wa s modulated by media factors, either exogenously added to the media or elaborated by the NIH3T3 cells themselves. This autologous stimulatio n of YY1 expression was in proportion to the density of cells and was time dependent. Sparsely plated cells lost YY1 RNA expression within h ours after being placed under fresh, serum-free media and lost YY1 pro tein expression by 24 h. Subsequent recurrence of YY1 expression in se rum-deprived NIH3T3 cells was significantly decreased by adding monocl onal anti-insulin-like growth factor (IGF)-1 to the media. Radioimmuno assay 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 aft er they became quiescent. In quiescent NIH3T3 cells, YY1 expression wa s low or absent but was rapidly stimulated by exposure of the quiescen t tells to medica-containing serum. Exogenous growth factors, either w hole 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 th e intranuclear responses to autologous stimulation by ICF-1.