Rapid degradation of c-fos proto-oncogene mRNA is crucial for transient c-fos gene expression. Experiments were performed to investigate the cellular mechanisms responsible for the extremely short half-life of human c-los mRNA in growth-factor-stimulated fibroblasts. These experiments demonstrate the existence of two distinct cellular pathways for rapid c-fos mRNA degradation. Each of these pathways recognizes a different, functionally independent instability determinant within the c-fos transcript. One instability determinant, which is located within the c-fos 3'-untranslated region, is a 75-nucleotide AU-rich segment. Insertion of this element into ~-globin mRNA markedly reduces the half-life of that normally long-lived message. Nevertheless, specific deletion of the AU-rich element from c-fos mRNA has little effect on the transcript's cytoplasmic halflife due to the presence of the other c-fos instability determinant, which is located in the protein-coding segment of the c-fos message. Examination of mRNA decay in cells treated with transcription inhibitors indicates that one c-fos mRNA degradation pathway is dependent on RNA synthesis, whereas the other is not.

Transcription of the c-fos proto-oncogene is rapidly induced in the rat pheochromocytoma PC12 cell line by a wide variety of stimuli, including polypeptide growth factors, phorbol esters, and calcium ion fluxes. We have mapped the upstream sequence requirements for this activation in PC12 cells by analysis of promoter deletion mutants in a transient expression assay. Two distinct pathways of c-fos induction are defined that differ in their requirement for cis-acting DNA sequences. Calcium activation of c-fos transcription is dependent on a DNA element located approximately 60 base pairs upstream of the transcription start site. This region is highly conserved between human, mouse, and chicken c-fos genes and contains a sequence that resembles the consensus for a cyclic AMP response element. The dyad symmetry element at position -300, which is necessary for serum responsiveness of c-fos, appears to be unimportant for calcium activation of the gene. The dyad symmetry element is, however, an essential cis-acting sequence for c-fos inducibility by nerve growth factor, epidermal growth factor, fibroblast growth factor, and the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate. Studies in vivo and in vitro with various mutants of the dyad symmetry element indicate that c-fos activation by polypeptide growth factors and 12-O-tetradecanoyl phorbol-13-acetate is mediated by a common transcription factor, and that this factor is identical to the previously described serum response factor. In vitro DNA-binding assays suggest that the quantity of serum response factor-binding activity remains unchanged during c-fos transcriptional activation.Expression of the c-fos proto-oncogene is rapidly and transiently activated in a variety of mammalian cell types by a diverse set of stimuli, including serum, specific polypeptide growth factors, phorbol esters, neurotransmitters, and agents that elevate intracellular calcium and cyclic AMP (cAMP) (3,5,6,12,13,15,16,23,24,29,(32)(33)(34)

In vitro mutagenesis of a 61-base-pair DNA sequence element that is necessary for induction of the c-fos proto-oncogene by growth factors revealed that a small region of dyad symmetry within the sequence element is critical for c-fos transcriptional activation. The same c-fos dyad symmetry element was found to bind a nuclear protein in vitro, causing a specific mobility shift of this c-fos regulatory sequence. An analysis of insertion and deletion mutants established a strict correlation between the ability of the dyad symmetry element to promote serum activation of c-fos transcription and in vitro nuclear protein binding. These experiments suggest that the DNA mobility shift assay detects a nuclear protein that mediates growth factor stimulation of c-fos expression. In vitro competition experiments indicate that the c-fos regulatory factor also binds to sequences within another growth factor-inducible gene, the I-actin gene.

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We give a new proof of the result, originally proved in unpublished work of Glenn Stevens [7], that every modular eigensymbol of non-critical slope lifts uniquely to a rigid-analytic distribution-valued eigensymbol. The proof is algorithmic and facilitates the efficient calculation of certain padic integrals.