INFLUENCE OF RAS AND RETINOIC ACID ON NERVE GROWTH-FACTOR INDUCTION OF TRANSIN GENE-EXPRESSION IN PC12 CELLS

Nerve growth factor (NGF)- and ras-induced neuronal differentiation of PC12 cells is accompanied by expression of transin, a secreted metall oproteinase. Retinoic acid (RA) is known to exert important effects on neural cell proliferation and differentiation, In this study we have analysed different PC12 sublines which express either activated Ras or dominant negative p21(N17) Ras, to evaluate the influence of retinoic acid (RA) on the response of the transin gene to NGF and Ras. There w as a good correlation between neurite extension and induction of trans in mRNA levels in the different subclones. NGF did not induce transin mRNA in cells which do not differentiate in response to this neurotrop hin. In addition, incubation with RA did not detectably increase basal transin mRNA levels, but caused a significant increase in the transin response to NGF or Ras in cells in which these factors induce a neuro nal morphology. Sequences contained within 750 base pairs of the 5' fl anking region of the transin gene confer responsiveness to NGF and Ras , but do not mediate the stimulatory effect of RA. In addition, expres sion of oncogenic Raf increases transin promoter activity in PC12 cell s, but a dominant-negative Raf mutant was unable to block NGF-induced transin activity suggesting the existence of a bifurcation downstream of ras in the signaling mechanism leading to transin expression by NGF .