Oncogene N-ras mediates selective inhibition of c-fos induction by nerve growth factor and basic fibroblast growth factor in a PC12 cell line.

Abstract

A cell line was generated from U7 cells (a subline of PC12 rat pheochromocytoma cells) that contains a stably integrated transforming mouse N-ras (Lys-61) gene under the control of the long terminal repeat from mouse mammary tumor virus. Such cells, designated UR61, undergo neuronal differentiation upon exposure to nanomolar concentrations of dexamethasone, as a consequence of expression of the activated N-ras gene (I. Guerrero, A. Pellicer, and D. E. Burstein, Biochem. Biophys. Res. Commun. 150:1185-1192, 1988. Exposure of UR61 cells to either nerve growth factor (NGF) or basic fibroblast growth factor (bFGF) results in a marked induction of c-fos RNA, with kinetics paralleling those of NGF-or bFGF-induced expression of c-fos RNA in PC12 cells. Dexamethasone-induced expression of activated N-ras p21 results in blocking of c-fos RNA induction by NGF or bFGF in a time-dependent manner. Activated N-ras p21-mediated inhibition of c-fos RNA induction in UR61 cells is selective for NGF and bFGF and is not due to selective degradation of c-fos RNA. Normal and transforming N-ras can trans activate the chloramphenicol acetyltransferase gene linked to mouse c-fos regulatory sequences when transient expression assays are performed. Our observations suggest that N-ras p21 selectively interacts with pathways involved in induction of c-fos expression which initiate at the receptors for NGF and bFGF.The ras genes were initially isolated as the transforming principle of certain oncogenic retroviruses (reviewed in reference 3). Cellular counterparts for these genes were subsequently found. A number of tumors contained ras alleles with transforming capacity in NIH 3T3 focus-forming assays, a capacity conferred by point mutations that lead to the expression of products with single amino acid substitutions (3). More recently, ras genes with transforming capacity for mouse fibroblasts have been shown to induce terminal differentiation in a number of cellular systems, including neuronal (4,28,49), endocrine (47), and lymphoid (54) On the basis of observation of ligand-mimicking effects and blocking by specific antibodies, several receptors for peptide growth factors have been proposed as candidates for interaction with ras p21, including the receptors for nerve growth factor (NGF) (4, 28, 29, 49), transforming growth factor 13 (50), and insulin (14,35).PC12 rat pheochromocytoma cells undergo neuronal differentiation and growth arrest when exposed to NGF (26). Interaction between this peptide and its surface receptor on PC12 cells is followed by transcriptional activation of specific sets of genes which are responsible for the resulting differentiated phenotype (reviewed in reference 26). NGFinduced transcriptional activation occurs according to distinct temporal patterns (39). One of the first genes whose expression is induced by NGF in PC12 cells is the nuclear proto-oncogene c fos (12,24,36). In the present study, we have used transient changes in the level of c-fos RNA as a marker for signal transduction (12,24,35) to analyze p...

Attenuated expression of the serum responsive T1 gene in ras transformed fibroblasts due to the inhibition of c-fos gene activity

“…Yu et al, (1993) have described the lack of c-fos, c-jun, junB and egr-1 expression in serum stimulated ras and src transformed rodent cell lines. Likewise, the absence of c-fos gene expression in ras transformed cells in response to TPA, PDGF, Ca 2+ ionophore, serum, and cAMP has been described by several authors (Lin et al, 1988;Mechta et al, 1997;Nose et al, 1989;Okimoto et al, 1996;Suzuki et al, 1989;Zullo and Faller, 1988) and NGF and bFGF mediated c-fos gene induction was found to be attenuated in N-ras transformed PC-12 cells (Thomson et al, 1990). In ras transformed Jurkat cells Ca 2+ in¯ux mediated c-fos and egr-1 gene expression is abolished .…”

Basic fibroblast growth factor transcriptional autoregulation requires EGR-1

“…Additionally, the bFGF promoter contains a functional AP-1 site. Very similar to Egr-1, c-jun and c-fos expression are rapidly activated by bFGF (Hall et al, 1991;Ito et al, 1990;Lampugnani et al, 1990;Thomson et al, 1990). It is therefore possible that AP-1 also controls the response to bFGF.…”

Influence of Ras and retinoic acid on nerve growth factor induction of transin gene expression in PC12 cells

“…UR61 cells contain a transfected ras oncogene under control of the inducible MMTV promoter (Guerrero et al, 1988;Thompson et al, 1990) and incubation with dexamethasone induces neurite extension (Figure 4c). Since the ras gene is involved in the action of NGF in PC12 cells, we examined the e ect of activated Ras on transin gene expression in UR61 cells.…”