Serum contains a macromolecular effector promoting the synthesis of nerve growth factor (NGF) in L cells

Autocrine regulation of neurite outgrowth from PC12 cells by nerve growth factor

The PC12 cell line may be used as a model of NGF-induced neuronal differentiation. Exposure to NGF is accompanied by extension of neurites, cessation of growth and differentiation into cells resembling sympathetic neurons. In this study neurite outgrowth from PC12 cells was induced in serum-free, NGF-free medium conditions. Neurite outgrowth in serum-free conditions was abolished by exposure to anti-NGF antisera. Reverse transcription combined with polymerase chain reaction (RT-PCR) and in situ hybridization of PC12 cells in serum-free medium conditions revealed NGF transcripts. Western blot analysis of these cells revealed tyrosine phosphorylation of the high affinity NGF receptor (TrkA/gp140) and activation of a downstream signal cascade element, ERK-1/MAP kinase. NGF was also detected by a specific enzyme-linked immunoabsorbant assay (ELISA) revealing picogram levels of protein in conditioned medium and cell lysates. Survival of embryonic rat dorsal root ganglion neurons was maintained in cultures grown in this serum-free conditioned medium. This demonstrated that NGF may act as an autocrine or paracrine growth factor for PC12 cell differentiation.

Expression of neurotrophin genes in human fibroblasts: differential regulation of the brain-derived neurotrophic factor gene

Brain-derived neurotrophic factor (BDNF), nerve growth factor (NGF) and neurotrophin-3 (NT-3) are structurally related survival and differentiation factors for distinct sets of peripheral and central neurons. We previously reported that BDNF and NGF gene expression are differentially regulated in mouse L929 fibroblasts. Here we examine expression of these three neurotrophins in human fibroblasts. Northern blots detected BDNF and NT-3 mRNAs in fibroblasts derived from lung (WI-38), calvarium and foreskin. WI-38 cells and foreskin fibroblasts expressed 1.6 kb as well as 4 kb BDNF mRNAs whereas only the smaller BDNF mRNA was detected in calvarium fibroblasts. NGF mRNA was present in foreskin and calvarium but not lung fibroblasts. In WI-38 cells serum treatment increased levels of BDNF mRNA within 2 hr. Cycloheximide did not inhibit the increase. Treatment with 12-O-tetradecanoyl phorbol-13-acetate (TPA) transiently suppressed BDNF mRNA. Treatment with both serum and TPA first stimulated and then transiently suppressed BDNF mRNA. TPA and/or serum did not significantly affect BDNF mRNA in calvarium fibroblasts. These results show that human fibroblasts derived from different tissues express and regulate neurotrophin genes differentially.

Differential regulation of the nerve growth factor and brain-derived neurotrophic factor genes in L929 mouse fibroblasts

Nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are structurally related survival and differentiation factors for distinct sets of peripheral and central neurons. The regulation of NGF gene expression has been extensively studied in L929 mouse fibroblasts. L929 cells also express the BDNF gene. Northern blot hybridization analysis revealed 4 discrete BDNF mRNA species in L929 cells and rat hippocampus after induction of seizures with kainic acid. Serum as well as 12-O-tetradecanoyl phorbol-13-acetate (TPA) stimulated NGF and all 4 BDNF mRNAs in L929 cells. Treatment with both agents induced NGF mRNA to a much larger extent than the BDNF mRNAs. The induction of the BDNF mRNAs was rapid, with nearly maximal levels by 1 hr. In contrast, NGF mRNA induction occurred later and peaked at 4-6 hr. Both NGF and BDNF mRNA induction were inhibited by actinomycin D. Cycloheximide, on the other hand, inhibited only NGF but not BDNF mRNA induction. Corticosterone rapidly decreased NGF mRNA but not the BDNF mRNAs, and had no effect on seizure-induced NGF or BDNF mRNAs. Forskolin did not stimulate NGF or BDNF mRNAs. In contrast to NGF mRNA, forskolin did not interfere with the serum induction of BDNF mRNAs. These results demonstrate that 2 genes which encode closely related neurotrophic factors are differentially regulated in L929 cells. The molecular mechanisms which bring about this differential regulation remain to be elucidated.

Induction of NGF by isoproterenol, 4-methylcatechol and serum occurs by three distinct mechanisms

Evidence is provided that isoproterenol, 4-methylcatechol and serum induce NGF by three separate mechanisms. Isoproterenol and 4-methylcatechol induced NGF and NGF mRNA in mouse fibroblast L929 cells in either the presence or absence of serum. Propranolol prevented NGF induction by isoproterenol, but not by 4-methylcatechol or serum. All possible combinations of these inducers resulted in additive increases in the levels of NGF and NGF mRNA.

1,25-Dihydroxyvitamin D3 is a potent inducer of nerve growth factor synthesis

1,25-Dihydroxyvitamin D3 (1,25-(OH)2D3), a metabolically active form of vitamin D, is shown to increase in a dose-dependent manner the cellular pool of NGF mRNA in murine L-929 fibroblasts cultured in a serum-free medium. This effect can be detected as early as 3 hours after 1,25-(OH)2D3 addition and persists for at least 28 hours. It is accompanied by an enhancement of the amount of NGF protein secreted in the culture medium. Since the proto-oncogene c-fos appears involved in the regulation of the NGF gene (Mocchetti et al.: Proceedings of the National Academy of Sciences of the United States of America 86: 3871-895, 1989; Hengerer et al: Proceedings of the National Academy of Sciences of the United States of America 87:3899-3903, 1990), the effect of 1,25-(OH)2D3 on c-fos expression was analysed and compared to that elicited by other inducers of the NGF gene, serum (Wion et al: FEBS Letters 189:37-41, 1985) and phorbol 12-myristate 13-acetate (PMA) (Wion et al: FEBS Letters 262:42-44, 1990). Addition of serum or PMA to L-929 cells was rapidly followed by a transient activation of the c-fos gene. In contrast, c-fos transcripts remained undetected in the presence of 1,25-(OH)2D3. The failure to find any evidence of c-fos expression suggests that 1,25-(OH)2D3 could enhance the pool of NGF mRNA by a mechanism independent of the c-fos pathway.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of nerve growth factor gene expression by 12-O-tetradecanoyl phorbol 13-acetate

Nerve injury leads to activation of fibroblasts, including stimulation of nerve growth factor (NGF) gene expression. Although interleukin-1 has been implicated as a mediator of NGF gene induction, the underlying mechanisms are not known. We investigated whether 12-O-tetradecanoyl phorbol 13-acetate (TPA), also a known stimulator of protein kinase C, regulates NGF gene expression. We show here that TPA stimulates NGF mRNA in mouse kidney and L929 fibroblasts but not in dispersed salivary cells. NGF mRNA stimulation in L929 cells is delayed by 2 h, is transient, and is followed by a parallel increase in NGF secretion. The induction of NGF mRNA is inhibited by cycloheximide, NGF mRNA levels decrease to similar values after 4 h of incubation with actinomycin D alone or in combination with TPA. These results indicate that the TPA response is cell specific and suggest that it is mediated at the transcriptional level via newly synthesized protein.

Phorbol 12-myristate 13-acetate (PMA) increases the expression of the nerve growth factor (NGF) gene in mouse L-929 fibroblasts

The rise of the NGF mRNA pool which takes place following exposure of L-929 fibroblasts to serum was prevented in the presence of 5 microM K-252a, a compound which inhibits several species of protein kinase activities. To characterize further this phenomenon, L-929 cells growing in a serum-free medium were exposed to cyclic nucleotide analogs, to a divalent cation ionophore or to the phorbol ester PMA. Only this latter compound induced an enhancement of the NGF mRNA pool, suggesting an involvement of protein kinase C in the upregulation of the NGF transcripts. The effects of PMA or serum also require a synthesis of protein since the level of NGF transcripts remained stable in the presence of cycloheximide.

Secretion of nerve growth factor in cultures of glial cells and neurons derived from different regions of the mouse brain

The regional ability of central neurons and glial cells to produce nerve growth factor (NGF) was studied in vitro. NGF secretion was compared in cultures of perinatal astrocytes or embryonic neurons that were derived from various mouse brain structures. No regional differences were detected among cultures of post-natal day 2 glial cells of hippocampal, cortical, striatal, or mesencephalic origin. In all cases, levels of NGF released by the cells were very similar. They were closely correlated to the growth rate as shown by the fact that exponentially growing cells produced relatively more factor than did confluent cells, a finding in agreement with previous observations. Unlike growth-phase cells, primary astrocytes immediately plated at high cell density did not secrete any assayable factor before the 7th day of culture. Levels of NGF found during the following days remained low. In contrast, striking differences were observed among cultures of embryonic neurons. NGF was found in relatively large amounts in cultures of embryonic day 17 or 19 striatal neurons, whereas media conditioned by neurons from the mesencephalon, cortex, or septum contained much less factor. Amounts of NGF assayed in cultures of hippocampal neurons varied with the time of sampling of this brain structure. Levels of factor were significantly higher in media conditioned by embryonic day 19 neurons than in media of embryonic day 17 neurons. However, amounts of NGF found in supernatants of hippocampal neurons remained smaller than those present in cultures of striatal nerve cells. Altogether, the results suggest that, in addition to astrocytes, central neurons may also synthesize and secrete NGF in vitro and that this phenomenum is dependent on both the origin and the developmental stage of the neuronal population.

Levels of nerve growth factor secreted by rat primary fibroblasts and iris transplants are influenced by serum and glucocorticoids

Previous work performed with mouse fibroblast-like L cells has shown that the level of expression of NGF gene is modulated in these transformed cells by the composition of the growth medium. Glucocorticoids were found to exert a down-regulation on NGF production, while serum stimulated the synthesis of the factor. The contrasting effects of serum and dexamethasone were further investigated in cultures of primary rat fibroblasts or in iris transplants. ELISA assays of NGF released by fibroblasts or by transplanted irides showed that both experimental systems responded to dexamethasone by a 4-5-fold decrease of the amounts of secreted factor. Half-maximal effect took place at a concentration of 3-5 X 10(-9) M, a value close to the dissociation constant of the glucocorticoid receptor in fibroblasts. The glucocorticoid did not influence the secretion of macromolecules. Assays of NGF mRNA performed at a concentration of 10(-7) M dexamethasone indicated that the steroid decreased the pool of NGF transcripts in either experimental systems. In contrast to dexamethasone, serum induced a 4-fold enhancement of the amounts of factor secreted by fibroblasts. This effect was reproduced with serum that was previously heat-treated at mild acidic pH, or with a macromolecular fraction of this heat-treated serum which contains an effector promoting NGF synthesis in L cells. The fact that promotion of NGF synthesis takes place in primary cells raises the possibility that this process may also occur in vivo, for instance following disruption of vasculature, as a part of a wound mechanism. Data collected with iris transplants provide some support to this interpretation.(ABSTRACT TRUNCATED AT 400 WORDS)