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Query: UNIPROT:P06889 (Mol)
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Cellular transition from the resting state to DNA synthesis involves master switches genes encoding transcriptional factors (e.g., fos, jun, and egr genes), whose targets remain to be fully characterized. To isolate coding sequences specifically accumulated in late G1, a differential screening was performed on a cDNA library prepared from hamster lung fibroblasts stimulated for 5 h with serum. One of the positive clones which displayed a sevenfold induction, turned out to code for a protein sharing homology to Ras-like products. Cloning and sequence analysis of the human homolog revealed that this putative new small GTPase, referred to as rhoG, is more closely related to the rac, CDC42, and TC10 members of the rho (ras homolog) gene family and might have diverged very early during evolution. rhoG mRNA accumulates in proportion to the mitogenic strength of various purified growth factors used for the stimulation, as a consequence of transcriptional activation. G1-specific RNA accumulation is impaired upon addition of antimitogenic cyclic AMP and is enhanced when protein synthesis is inhibited, mainly as a result of RNA stabilization. rhoG mRNA expression is observed in a wide variety of human organs but reaches a particularly high level in lung and placental tissues.
Mol Cell Biol 1992 Jul
PMID:Growth-regulated expression of rhoG, a new member of the ras homolog gene family. 162 Jan 21

The proteins encoded by cellular and viral src genes are believed to be involved in the transmission of mitogenic signals, the nuclear recipients of which are largely unknown. In this work, we report that four different v-src-transformed cell lines from three different species possess elevated levels of junB transcripts. Transient expression of junB promoter-chloramphenicol acetyltransferase constructs in NIH 3T3 cells was used to demonstrate that the increase in junB transcripts was specifically associated with v-src expression and could not be recapitulated with a c-src, v-H-ras, or v-raf expression vector. Deletion mutants were used to localize the v-src-responsive region in the junB promoter to a 121-nucleotide region encompassing the CCAAT and TATAA elements. This region is distinct from one in the 5' untranslated region of the junB gene which is required to maintain its high-level basal expression. Point mutagenesis of the junB TATAA box completely abolished v-src responsiveness, suggesting that proteins which bind to this element are modified by src transformation. Several v-src and c-src mutants were used to demonstrate that elevated tyrosine kinase activity of src proteins is required for the observed effects on junB expression. Finally, homology between the TATAA box regions of junB and the unrelated but src-responsive gene 9E3/CEF-4 suggests that modulation of gene activity through proteins which bind to this region may be a recurrent, although not exclusive, theme in src transforming action. Our results suggest that src proteins may modulate some nuclear effectors through pathways not involving cellular ras or raf gene products.
Mol Cell Biol 1992 Aug
PMID:Regulation of the junB gene by v-src. 163 Apr 51

The c-, L-, and N-Myc nuclear phosphoproteins share several highly conserved regions that partially overlap putative functional domains of the c-Myc protein. All three myc oncogenes can cooperate with an activated ras gene to transform primary rat embryo cells (REC), and deregulated expression of c- and L-myc can block differentiation of murine erythroleukemia (MEL) cells. In the present study, we demonstrate that N-myc also can block MEL cell differentiation, and we identify regions within the c-Myc protein that are necessary for inhibition of MEL differentiation. C19 MEL cells were transfected with six human c-myc genes which were partially deleted in different areas of the coding region. Four of the genes lack sequences that overlap either the putative transcriptional activation domain, the helix-loop-helix motif, or the leucine zipper motif and were previously shown to have lost REC cotransforming activity (J. Stone, T. DeLange, G. Ramsay, E. Jakobovitz, J.M. Bishop, H. Varmus, and W. Lee, Mol. Cell. Biol., 7: 1697-1709, 1987). In this study, we demonstrate that they also fail to inhibit N,N'-hexamethylene-bis-acetamide-induced differentiation of MEL cells. In contrast, two partially deleted c-myc genes, one lacking a short NH2-terminal region and the other lacking 118 amino acids at the center of the coding region, which were fully active in REC cotransformation, also exhibited full activity associated with the former and only partial activity with the latter in blocking MEL differentiation. We conclude that the mutated genes tested in this study behave similarly in inhibition of MEL cell differentiation and in REC cotransformation.
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PMID:Regions within the c-Myc protein that are necessary for transformation are also required for inhibition of differentiation of murine erythroleukemia cells. 163 9

Stromelysin gene expression is transcriptionally activated by a number of growth factors (e.g., EGF and PDGF), tumor promoters (e.g., TPA), and oncogenes (e.g., ras, src) through an AP-1-dependent mechanism. TGF-beta repression of stromelysin induction is mediated at the level of transcription by an element located at position -709 in the rat stromelysin promoter referred to as the TGF-beta inhibitory element (TIE). A TIE-binding protein complex is induced by treatment of rat fibroblasts with TGF-beta. This protein complex contains the protooncogene c-fos, and induction of c-fos by TGF-beta is required for the repressive effects of TGF-beta on stromelysin gene expression. Interestingly, c-fos induction is also required for stimulation of stromelysin expression by EGF in rat fibroblasts. Preliminary studies suggest that differential regulation of members of the jun family of early-response genes may explain this apparent paradox and determine whether stromelysin is induced or repressed by growth factors. TGF-beta stimulation therefore initiates a cascade of events that results in a specific pattern of gene expression: the direct stimulation of early-response genes can lead to subsequent induction or repression of other genes. Growth factor regulation of matrix metalloproteinases appears to play a role in embryonic development in the morphogenesis of the murine lung. Treatment of embryonic lungs in organ culture with the growth factors EGF or TGF-alpha results in stimulation of growth and inhibition of branching morphogenesis. A similar inhibition of branching was observed when these lung rudiments were treated with the matrix metalloproteinase collagenase. Most interestingly, the effects of EGF and TGF-alpha can be completely reversed by the tissue inhibitor of metalloproteinases, TIMP. TGF-beta has the opposite effect on growth of murine lung rudiments--growth is inhibited in a dose-dependent manner. This example illustrates a potential role for growth factor regulation of matrix-degrading metalloproteinases in complex developmental processes.
Mol Reprod Dev 1992 Jun
PMID:Negative regulation of gene expression by TGF-beta. 163 49

We have isolated two cDNAs encoding small GTP-binding proteins from leaf cDNA libraries. These cDNAs encode distinct proteins which show considerable homology to members of the ras superfamily. Np-ypt3, a 1044 bp long Nicotiana plumbaginifolia cDNA, encodes a 24.4 kDa protein which shows 65% amino acid sequence similarity to the Schizosaccharomyces pombe ypt3 protein. The N-ypt3 gene is differentially expressed in mature flowering plants. Expression of this gene is weak in leaves, higher in stems and roots, but highest in petals, stigmas and stamens. Nt-rab5, a 712 bp long Nicotiana tabacum SR1 cDNA, encodes a 21.9 kDa protein which displays 65% amino acid sequence similarity to mammalian rab5 proteins. The expression pattern of the Nt-rab5 gene is very similar to that of the Np-ypt3 gene. The Nt-rab5 gene is virtually not expressed in leaves, higher in stems and roots, and highest in flowers. Both the Nt-rab5 and Np-ypt3 proteins were expressed in Escherichia coli and shown to bind GTP.
Plant Mol Biol 1992 Aug
PMID:Molecular characterization of tobacco cDNAs encoding two small GTP-binding proteins. 164 85

The suspect human hepatocarcinogen aflatoxin B1 (AFB1) is a well-known potent initiator of hepatic tumors in rainbow trout (Oncorhynchus mykiss). Both hepatocellular carcinomas and mixed hepatocellular/cholangiocellular carcinomas are induced by AFB1 in trout, with the mixed form predominating. We previously isolated two c-ras genes from trout liver cDNA, and in the present study we analyzed DNA from 14 AFB1-induced trout liver tumors for point mutations in exon 1 of both genes. Using the polymerase chain reaction (PCR) and oligonucleotide hybridization methods, a high proportion (10/14) of the AFB1-initiated tumor DNAs showed evidence of activating point mutations in the trout c-Ki-ras gene. Of the 10 mutant ras genotypes, seven were codon 12 GGA----GTA transversions, two were codon 13 GGT----GTT transversions, and one was codon 12 GGA----AGA transition. Nucleotide sequence analysis of cloned PCR products from four of these tumor DNAs provided definitive evidence for two codon 12 GGA----GTA mutations, one codon 12 GGA----AGA mutation, and one codon 13 GGT----GTT mutation, in complete agreement with the oligonucleotide hybridization results. No mutations were detected in exon 1 of a second trout ras gene also expressed in liver, nor in DNA from control livers. This is the first report of experimentally induced ras gene point mutations in a lower vertebrate fish model. The results indicate that the hepatocarcinogen AFB1 induces c-Ki-ras gene mutations in trout similar to those in rat liver tumors.
Mol Carcinog 1991
PMID:Analysis of ras gene mutations in rainbow trout liver tumors initiated by aflatoxin B1. 164 72

Gap junctional intercellular communication is inhibited in response to tumor promoters and oncogene transformation, suggesting that loss of this function is an important step in tumor formation. To elucidate the molecular mechanisms responsible for this inhibition, we examined the expression of gap junction proteins and mRNA in mouse primary keratinocytes after treatment with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) and/or ras transformation. During normal cell growth, keratinocytes expression the alpha 1 (connexin 43) and beta 2 (connexin 26) proteins. Within 5 min of TPA treatment, the alpha 1 protein became rapidly phosphorylated on serine residues and its expression was dramatically reduced by 24 h. The beta 2 protein, after an initial increase in expression, was also significantly reduced 24 h after treatment with TPA. ras transformation caused changes similar to those induced by TPA. The alpha 1 protein underwent an increase in serine phosphorylation, although its expression declined only slightly, while beta 2 expression was greatly reduced. The effects of TPA and ras on alpha 1 expression were additive; treatment of ras-transformed cells with TPA resulted in increased alpha 1 phosphorylation, with greatly decreased protein levels, much lower than those generated by either agent alone. These data provide a likely explanation for the similar and synergistic inhibition of gap junctional intercellular communication by phorbol esters and ras.
Mol Cell Biol 1991 Oct
PMID:The tumor promoter 12-O-tetradecanoylphorbol-13-acetate and the ras oncogene modulate expression and phosphorylation of gap junction proteins. 165 30

Insulin induces a rapid activation of p21ras in NIH 3T3 and Chinese hamster ovary cells that overexpress the insulin receptor. Previously, we suggested that p21ras may mediate insulin-induced gene expression. To test such a function of p21ras more directly, we studied the effect of different dominant inhibitory mutants of p21ras on the induction of gene expression in response to insulin. We transfected a collagenase promoter-chloramphenicol acetyltransferase (CAT) gene or a fos promoter-luciferase gene into NIH 3T3 cells that overexpressed the insulin receptor. The activities of both promoters were strongly induced after treatment with insulin. This induction could be suppressed by cotransfection of two inhibitory mutant ras genes, H-ras(Asn-17) or H-ras(Leu-61,Ser-186). In particular, insulin-induced activation of the fos promoter was inhibited completely by H-ras(Asn-17). These results show that p21ras functions as an intermediate in the insulin signal transduction route leading to the induction of gene expression.
Mol Cell Biol 1991 Dec
PMID:Two dominant inhibitory mutants of p21ras interfere with insulin-induced gene expression. 165 21

We have previously used a series of insertion-deletion mutants of the mutationally activated v-rasH gene to identify several regions of the encoded protein that are dispensable for cellular transformation (B. M. Willumsen, A. G. Papageorge, H.-F. Kung, E. Bekesi, T. Robins, M. Johnsen, W. C. Vass, and D. R. Lowy, Mol. Cell. Biol. 6:2646-2654, 1986). To determine if some of these amino acids are more important for the biological activity of c-rasH, we have now tested many of the same insertion-deletion mutants in the c-rasH form for their ability to transform NIH 3T3 cells. Since the transforming activity of c-rasH is low, we have used cotransfection with the bovine papillomavirus (BPV) genome to develop a more sensitive transformation assay for c-rasH mutants. The increased sensitivity of the assay, which is seen both in focal transformation and in anchorage-independent growth, is mediated by cooperation between the BPV E5 gene and ras. E5-dependent cooperation was seen for v-rasH as well as for c-rasH, which suggests that the major effect of E5 was to increase the susceptibility of the cell to transformation to a given level of ras activity. The cooperation assay was used to test the potential importance, in c-rasH, of codons 93 to 108, 123 to 130, and 166 to 183, which were nonessential for v-rasH transformation. Relative to the respective transforming activity of wild-type c-rasH and v-rasH, mutants with lesions in codons 102 and 103 were significantly less active in their c-rasH forms than in their v-rasH forms. We conclude that a region including amino acids 102 and 103 encodes a function that is more critical to c-rasH than to v-rasH. Guanine nucleotide exchange is one function that is compatible with such a phenotype.
Mol Cell Biol 1991 Dec
PMID:The bovine papillomavirus E5 oncogene can cooperate with ras: identification of p21 amino acids critical for transformation by c-rasH but not v-rasH. 165 23

We used a series of cell clones from a human teratocarcinoma cell line, PA-1, to study the effect of transformation by an activated N-ras oncogene on the expression of genes involved in retinoic acid (RA)-induced differentiation and growth regulation. Recently, it has been shown that expression of human HOX 2 genes is sequentially activated by RA beginning from Hox 2.9 at the 3' end of the HOX 2 cluster (A. Simeone, D. Acampora, L. Arcioni, P. W. Andrews, E. Boncinelli, and F. Mavilio, Nature [London] 346:763-766, 1990). We now report that six different genes of the cluster HOX 1 are sequentially induced by RA in a similar temporal pattern, beginning with genes at the 3' end of the cluster. However, in N-ras-transformed cell clones, RA-induced expression of these homeobox genes is delayed. Hox 1.4 and Hox 1.3, genes abundantly induced in nontransformed clones after 3 days of RA treatment, are expressed in N-ras-transformed cells only after 10 days of RA treatment. At this time, the cells' growth is arrested at very high density, and no differentiated morphologic characteristics are observed. Constitutive expression of a transfected Hox 1.4 gene under the control of a simian virus 40 promotor leads to differentiated cell morphology similar to that of the RA-induced phenotype and restores the growth-inhibitory effects of RA in N-ras-transformed cells. These observations provide evidence that enhanced proliferation in N-ras-transformed cells compromises teratocarcinoma cell differentiation by a mechanism that transiently suppresses homeobox gene induction and implies a central role for homeobox genes in RA-induced cell differentiation. We conclude that stimulation of a putative growth factor signal pathway, associated with ras-induced proliferation, transiently suppresses the induction of transcription factors functionally involved in cell growth and differentiation.
Mol Cell Biol 1991 Jul
PMID:Alteration of homeobox gene expression by N-ras transformation of PA-1 human teratocarcinoma cells. 167 27


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