Normal and activated ras oncogenes and their encoded products

N-Ras Mutations in Myeloid Leukemias

The presence of mutations activating the N-ras gene was investigated by the polymerase chain reaction technique in twenty patients with acute myeloblastic leukemia (AML) at onset and in four patients with Ph' positive chronic myelogeneous leukemia (CML) either in chronic phase or in blast crisis. Four remission samples and four relapses from the AML cases were also studied. Mutations were found in five out of twenty (25%) untreated AML cases at onset. No mutations were detected in the complete remission samples, two of them with N-ras mutations during the leukemic phase. Two out of the four leukemia relapses were positive for the same N-ras mutation shown at presentation, whereas no new mutations were found in the other two initially negative cases. An N-ras mutation appeared during the blast crisis of one of the four CML, which were all negative during the chronic phase. In conclusion, whereas some data appear to be consistent with a role of the N-ras mutations as initiating events in myeloid leukemias, in other cases N-ras activation seems to represent a factor involved in progression. These data suggest that a partial overlapping between initiation and progression factors could exist in naturally occurring tumors.

Ribosome-induced tuning of GTP hydrolysis by a translational GTPase

GTP hydrolysis by elongation factor Tu (EF-Tu), a translational GTPase that delivers aminoacyl-tRNAs to the ribosome, plays a crucial role in decoding and translational fidelity. The basic reaction mechanism and the way the ribosome contributes to catalysis are a matter of debate. Here we use mutational analysis in combination with measurements of rate/pH profiles, kinetic solvent isotope effects, and ion dependence of GTP hydrolysis by EF-Tu off and on the ribosome to dissect the reaction mechanism. Our data suggest that--contrary to current models--the reaction in free EF-Tu follows a pathway that does not involve the critical residue H84 in the switch II region. Binding to the ribosome without a cognate codon in the A site has little effect on the GTPase mechanism. In contrast, upon cognate codon recognition, the ribosome induces a rearrangement of EF-Tu that renders GTP hydrolysis sensitive to mutations of Asp21 and His84 and insensitive to K(+) ions. We suggest that Asp21 and His84 provide a network of interactions that stabilize the positions of the γ-phosphate and the nucleophilic water, respectively, and thus play an indirect catalytic role in the GTPase mechanism on the ribosome.

[Genic alterations in oral and head and neck squamous cell carcinomas: analysis of international literature]

The development of oral and head and neck squamous cell carcinomas occurs in relation with multiple events including mainly: loss of cycle cell control, evasion from apoptosis, telomerase reactivation. Complex interactions between a set of molecules, cell cycle proteins, tumour suppressor genes, oncogenes and the telomerase, occur in the multiple step process of carcinogenesis. The 2 main ways of control of the cell cycle rely on 2 tumour suppressor genes: the P53 gene and the retinoblastoma gene or RB gene. One of the regulation pathways or the 2 regulation pathways are disabled during the development of oral and head and neck squamous cell carcinomas. Most of the time, the inactivation of the P53 pathway results from a loss of function of the p53 protein, secondary to mutation and/or deletion of the P53 gene; It may also result of the amplification of the MDM2 gene and of the inactivation of the arf protein. The RB pathway leads to cell proliferation by loss of the p16 protein, by amplification of the cyclin D1 gene and less frequently by mutation of the RB gene or loss of the retinoblastoma protein. In India and South-East Asia, the activation of RAS and MYC oncogenes appears to be related with the presence of specific carcinogens in snuff and tobacco. By blocking apoptosis, the Bcl2 protein seems to increase the resistance of tumours to radiotherapy and chemotherapy.

Isolation of a novel gene from Schizosaccharomyces pombe: stm1+ encoding a seven-transmembrane loop protein that may couple with the heterotrimeric Galpha 2 protein, Gpa2

A putative seven transmembrane protein gene, stm1(+), which is required for proper recognition of nitrogen starvation signals, was isolated as a multicopy suppressor of a ras1 synthetic lethal mutant in Schizosaccharomyces pombe. Under nitrogen-deficient conditions, transcription of the stm1 gene was induced; deletion of stm1 was associated with early entry into G(1) arrest. Under nutritionally sufficient conditions, overexpression of Stm1 inhibited vegetative cell growth, resulted in decreased intracellular cAMP levels, increased the expression of the meiosis-specific genes ste11, mei2, and mam2, and facilitated sexual development in homothallic cells. However inhibition of vegetative cell growth and reduction of cAMP levels were not observed in a deletion mutant of the heterotrimeric G protein Galpha2 gene, gpa2, that is responsible for regulating intracellular cAMP levels, a key factor in determining the sexual development in S. pombe. Stm1 protein was shown to interact with Gpa2 through its C-terminal transmembrane domains 5-7. Mutation at Lys(199) in the C-terminal domain (stm1(K199A)) abolished the Stm1 overexpression effect on lowering cAMP levels. Induction of ste11, a meiosis-specific gene transcription factor, by Stm1 overexpression was enhanced in gpa2-deleted cells but was absent in a deletion mutant of sty1, a key protein kinase that links mitotic control with environmental signals and induces stress-responsive genes. Moreover, deletion of both stm1 and ras1 caused delayed entry into G(1) arrest in S. pombe when the cells were grown in a nitrogen-deficient medium. Thus we consider that the stm1 gene can function through Gpa2-dependent and/or -independent pathways and may play a role in providing the prerequisite state for entering the pheromone-dependent differentiation cycle in which heterotrimeric Galpha1 protein, Gpa1, and Ras1 play major roles. Stm1 could function as a sentinel molecule sensing the nutritional state of the cells, stopping the proliferative cell cycle, and preparing the cell to enter meiosis under nutritionally deficient conditions.

Molecular genetics of human retinal disease

The past decade has witnessed extraordinary progress in retinal disease gene identification, the analysis of animal and tissue culture models of disease processes, and the integration of this information with clinical observations and with retinal biochemistry and physiology. During this period over twenty retinal disease genes were identified and for many of these genes there are now significant insights into their role in disease. This review presents an overview of the basic and clinical biology of the retina, summarizes recent progress in understanding the molecular mechanisms of inherited retinal diseases, and offers an assessment of the role that genetics will play in the next phase of research in this area.

p53 and ras mutations in Ewing's sarcoma

The role of tumor suppressor genes and oncogenes in the development of Ewing's sarcoma has not yet been fully clarified. In this study, we analyzed the frequency of p53 tumor suppressor gene mutation in exons 4-8 by PCR-SSCP and direct sequencing, and the expression of p53-protein in Ewing's sarcoma (ES) by using immunohistochemistry. The overexpression of MDM2, which acts as a functional inactivator of p53, was studied by immunohistochemistry. In addition, a screening for point mutations in the hot spot regions codon 12 and 13 of exon 1 and codon 61 of exon 2 of ras-genes (H-ras, N-ras, K-ras) was performed. In one case, a p53 gene mutation could be confirmed in codon 238 of exon 7 (1/24). Overexpression of MDM2 was found in five cases; in ras-genes, no mutations were detected. Compared with other highly malignant mesenchymal pediatric tumors such as osteosarcomas, mutations of p53 and ras in Ewing's sarcomas are an extraordinarily rare event. However, their frequency is comparable to that of PNET, suggesting that the low incidence of these mutations in ES and PNET could be group-specific for tumors of neuroectodermal genesis.

Review article: The role of oncogenes, tumour suppressor genes and growth factors in oral squamous cell carcinoma: a case of apoptosis versus proliferation

Mutation, deactivation and disregulated expression of oncogenes and tumour-suppressor genes may be involved in the pathogenesis of oral squamous cell carcinoma (SCC). Deactivation of the p53 tumour-suppressor gene allows cell proliferation and blocks apoptosis of malignant oral keratinocytes. Mutation in the ras oncogene results in persistent mitogenic signalling. Upregulatioed c-Myc expression, in the presence of growth factors, provides an additional proliferative signal. Loss of retinoblastoma tumour-suppressor gene (Rb) function may contribute to oral keratinocyte hyperproliferation and recent evidence suggests that simultaneous deactivation of both p53 and Rb is required for tumourigenesis. Enhanced Bcl-2 and reduced Fas expression inhibit tumour cell apoptosis and may convey resistance to cytotoxic drugs and T cell-mediated cytotoxicity, respectively. Exogenous mutagens such as tobacco, alcohol and viral oncogenes may cause altered expression of oncogenes and tumour-suppressor genes in some cases of oral SCC. The impact of these mechanisms on future therapies for oral SCC is highlighted.

Cyclic AMP decreases chemotaxis, invasiveness and lung colonization of H-ras transformed mouse fibroblasts

We transfected mouse 10T1/2 fibroblasts with the H-ras oncogene and isolated lines expressing H-ras. One of the lines exhibited a highly malignant phenotype with the ability to produce large tumors and to colonize the lung after tail vein injection. In addition, the cells of this line showed increased collagenase IV production, directed migration and invasiveness, properties associated with the ability of tumor cells to metastasize. Since cyclic adenosine 3',5'-monophosphate (cAMP) is known to down-regulate ras expression, we exposed the malignant cells (Cl-1) to either N6, 2',0-dibutyryl cAMP (DB-cAMP) or 8-bromo cAMP (8-Br-cAMP), either with or without a phosphodiesterase inhibitor. We found that these treatments reduced the expression of ras, chemotaxis, invasiveness, and lung colonization of the ras-transformed cells. We therefore postulate that the malignancy of some cells may be regulated by alterations in the intracellular cAMP levels by suppressing ras expression and/or by reducing other activities required for the dissemination of tumor cells.

Association of ras p21 with differentiation of epidermal keratinocytes in proliferating skin diseases

We examined the localization of DNA replicating cells and ras oncogene product p21 positive cells in proliferating skin diseases, such as psoriasis vulgaris, lichen planus, verruca vulgaris, verruca plana juvenilis and seborrheic keratosis. ras p21-positive cells were found rather in the differentiated layers than in the proliferating layers of the epidermis. We indicate that the expression of ras p21 can be associated with the differentiation of epidermal keratinocytes not only in tumor tissues but also in inflammatory skin disease.

Proto-oncogenes in the regulatory circuit for myogenesis

Skeletal muscle cells have provided an auspicious system for dissecting the mechanisms through which growth factor signals disrupt programs for cellular differentiation. Insight into the molecular mechanisms that control muscle differentiation has recently been obtained through the cloning of a family of muscle-specific transcription factors, often referred to as the MyoD family, that can activate myogenesis. The expression and activity of these factors are negatively regulated by growth factor signals and by activated oncogenes whose products transduce growth signals from the cell membrane to the nucleus. This review will focus on the role of proto-oncogenes in the transduction of growth factor signals that regulate myogenesis and on the cross-talk between the regulatory circuits that control myoblast proliferation and differentiation.

Use of a reconstituted basement membrane to study the invasiveness of tumor cells

We have used an extract of basement membranes which can be reconstituted into a biologically active gel matrix composed predominantly of collagen IV, laminin, nidogen, and heparin sulfate proteoglycan, in order to study the mechanisms involved in tumor cell invasion. When layered onto a porous filter in a Boyden chamber, the gel forms a barrier to the passage of normal cells. Malignant cells are able to cross this layer when the conditioned medium of NIH 3T3 cells is used as a chemoattractant to stimulate cell migration. A variety of human tumor cells have thus been studied in this system and we find a high correlation between their invasiveness in vitro and their malignant behavior as exhibited in vivo. We have used this in vitro invasion assay to test for factors which might inhibit tumor cell invasion. Collagenase IV is produced by malignant cells and is thought to be required for invasion. Indeed, inhibitors of this enzyme have demonstrated reduced tumor cell invasiveness. One site of five amino acids, on the B1 chain, which has been shown to promote cell adhesion, migration and binding to laminin receptor, was found to inhibit the invasion of tumor cells. In addition, factors which elevated cAMP levels were also able to suppress the invasiveness of tumor cells. These data suggest that the assay system described herein can be successfully utilized to study the invasive activity of tumor cells and those factors that may inhibit the spread of malignant cells.

The functional psychoses--are oncogenes involved in their pathogenesis? Some speculations

Oncogenes are genes whose expression has been associated with malignant transformation of cells in tissue culture and with neoplastic changein vivo(Bishop, 1987). Much of the current understanding of their nature and action has stemmed from work, over the past 20 years, on tumour viruses (Temin, 1971; Rapp, 1983). One group of tumour viruses, the retroviruses, are unique in possessing an enzyme, reverse transcriptase, which transcribes to the cell DNA a copy of the viral RNA genome (Marks, 1987). After the discovery of viral oncogenes, such DNA copies were used as probes in hybridisation studies (Stehelinet al, 1976; Frankel & Fischinger, 1976). These probes, capable of annealing to complementary DNA sequences, revealed the existence of the latter in normal, unaffected cells (Willecke & Schäfer, 1984). These sequences, called cellular or proto-oncogenes, exist in a wide range of eukaryotic organisms, from yeast to man.

RAS oncogene product expression in normal and malignant oral mucosa

Proto-oncogenes are important in both normal cellular differentiation and in carcinogenesis. The majority of transforming genes belong to the ras family and the ras gene product has been shown to be elevated in some oral carcinomas. RAP-5 monoclonal antibody was used to determine the expression of the p21ras protein in normal and neoplastic oral mucosa in an immunohistological study. The expression of p21ras protein was generally restricted to acanthous cells with strong staining in normal oral mucosa and well-differentiated carcinomas. In contrast, the p21ras protein was not detected in significant amounts in severely dysplastic lesions and poorly differentiated carcinomas. These results suggest that expression of p21ras is a normal feature of more fully differentiated tissues, both normal and neoplastic, and is not useful as an indicator of cell proliferation or 'malignant potential'.

Evolution of proteins of the cystatin superfamily

We have examined the amino acid sequences of a number of proteins that have been suggested to be related to chicken cystatin, a protein from chicken egg white that inhibits cysteine proteinases. On the basis of statistical analysis, the following proteins were found to be members of the cystatin superfamily: human cystatin A, rat cystatin A(alpha), human cystatin B, rat cystatin B(beta), rice cystatin, human cystatin C, ox colostrum cystatin, human cystatin S, human cystatin SA, human cystatin SN, chicken cystatin, puff adder cystatin, human kininogen, ox kininogen, rat kininogen, rat T-kininogens 1 and 2, human alpha 2HS-glycoprotein, and human histidine-rich glycoprotein. Fibronectin is shown not to be a member of this superfamily, and the c-Ha-ras oncogene protein p21 (Val-12) probably is not a member also. It was convenient to divide members of the superfamily into four types on the basis of the presence of one, two, or three copies of cystatin-like segments and the presence or absence of disulfide bonds. Evolutionary dendrograms were calculated by three methods, and from these we have constructed a scheme depicting the sequence of events in the evolution of these proteins. We suggest that about 1000 million years ago a precursor containing disulfide loops appeared, and that all disulfide-containing cystatins are derived from this. We follow the evolution of the proteins of the superfamily along four main lineages, with special attention to the part that duplication of segments has played in the development of the more complex molecules.

Molecular oncogenetics of metastasis

Metastasis is a complex non-stochastic process that is most likely the result of genetic and epigenetic interactions of a wide variety of genes. The search for a single gene which can encompass such a pleiotropic response as to account for the observed phenotypic characteristics of metastatic tumour populations has been unsuccessful. Particular studies involving gene transfection, subtractive hybridisation and cell fusion are beginning to identify specific genes which contribute to metastasis in some cell types. However, such analyses are complicated by the inherent genetic instability and phenotypic heterogeneity present in tumour populations. A more detailed understanding of the metastatic process may require an abandoning of current generalised approaches to metastasis in favour of concentrating on key components of the metastatic cascade such as adhesion and invasion.

High p21RAS expression levels correlate with chromosome 8 rearrangements in benign human mixed salivary gland tumors

The expression of RAS oncogenes in benign and malignant salivary gland tumors was studied by immunohistochemistry and by immunoblotting using monoclonal antibodies recognizing the HRAS and KRAS gene products. Twenty-eight out of 29 benign pleomorphic adenomas overexpressed p21RAS, whereas only 12 out of 18 malignant salivary gland tumors expressed the p21 protein. The expression levels were also substantially higher in the adenomas than in the malignant tumors, indicating that RAS gene activation appears to be more frequent and of greater importance for benign than for malignant salivary gland tumors. Comparisons of the p21 expression levels with the karyotypes of the pleomorphic adenomas revealed a novel correlation between high p21 expression and chromosome 8 rearrangements. As a hypothesis, it is suggested that a novel gene located on the proximal long arm of chromosome 8, most likely at band q12, is involved in the regulation of RAS gene expression.

Oncogenicity of human N-ras oncogene and proto-oncogene introduced into retroviral vectors

The N-ras gene is the only member of the ras family which has never been naturally transduced into a retrovirus. In order to study the in vitro and in vivo oncogenicity of N-ras and to compare its pathogenicity to that of H-ras, we have inserted an activated or a normal form of human N-ras cDNA into a slightly modified Harvey murine sarcoma virus-derived vector in which the H-ras p21 coding region had been deleted. The resulting constructions were transfected into NIH 3T3 cells. The activated N-ras-containing construct (HSN) induced 10(4) foci per microgram of DNA and was found to be as transforming as H-ras was. After infection of the transfected cells by either the ecotropic Moloney murine leukemia virus or the amphotropic 4070A helper viruses, rescued transforming viruses were injected into newborn mice. Both pseudotypes of HSN virus containing activated N-ras induced the typical Harvey disease with similar latency. However, we found that the virus which contained normal N-ras p21 (HSn) was also pathogenic and induced splenomegaly, lymphadenopathies, and sarcoma in mice after a latency of 3 to 7 weeks. In addition, Moloney murine leukemia virus pseudotypes of N-ras caused neurological disorders in 30% of the infected animals. These results differed markedly from those of previous experiments in which we had inserted the activated form of N-ras in the pSV(X) vector: the resulting SVN-ras virus was transforming on NIH 3T3 cells but was poorly oncogenic in vivo (M. Souyri, C. F. Koehne, P. V. O'Donnel, T. H. Aldrich, M. E. Furth, and E. Fleissner, Virology 158:69-78). However, similarly poor oncogenicity was also observed when the v-H-ras coding sequence was inserted in pSV(X) vector, which indicated that the vector sequences play a crucial role in the pathogenicity of a given oncogene. Altogether, these data demonstrated unequivocally that N-ras is potentially as oncogenic as H-ras and that such oncogenic effect could depend on the vector environment.

RAS enzyme-linked immunoblot assay discriminates p21 species: a technique to dissect gene family expression

The members of the RAS gene family of protooncogenes are of implied biological significance in oncogenesis. The precise role of these genes is unclear. One difficulty has been the inability to discriminate the individual p21 protein products of various ras genes in cell lines, de novo human tumors, and related normal tissues. In this report, specific proteins of the human c-Ha-ras-1, c-Ki-ras-2, and c-N-ras genes have been detected and discriminated by the differential use of various antisera recognizing these p21s. This enzyme-linked immunoblot assay utilizes a double antibody system in which monoclonal antibodies are initially used to immunoprecipitate the p21ras proteins. Immunoprecipitates are then subjected to one-dimensional Western blot analysis utilizing other antibodies raised against p21s, coupled with nonradiolabeled enzyme-linked colorimetric detection. By direct detection, the specific products of the three human ras genes can be discriminated. In addition, we describe the generation and characterization of a new anti-p21c-N-ras-specific antibody. The simultaneous expression into protein of multiple ras genes is unequivocally demonstrated in both homogeneous cell lines and heterogeneous human tissues. This new technique is also applicable for discrimination of the protein products of other gene families.

Endocytosis and inositol hexakisphosphate levels in ras transformants of Dictyostelium discoideum amoebae

Fluid-phase pinocytosis kinetics and lysosomal enzyme secretion parameters were measured in Dictyostelium discoideum amoebae constructed from strain AX3 by transformation with a multicopy plasmid carrying either a normal ras gene (ras-Gly12), a mutated ras gene (ras-Thr12) or by the vector carrying the geneticin resistance gene only (pDNEO2). It was found that the pinocytosis rate and extent as well as the lysosomal enzyme secretion were slightly different in the three strains. These changes, however, were related to minor modifications of the cellular volumes. The overall concentration of inositol hexakisphosphate was similar in the three strains.

Co-regulation of metastatic and transforming activity of normal and mutant ras genes

We have analyzed the metastatic properties of NIH-3T3 cells transformed by H-ras activated through over-expression and/or mutation. Our results reveal that elevated expression of H-ras proto-oncogene can induce the complete metastatic phenotype. Cells transformed by the proto-oncogene have a lower metastatic potential than those transformed by a mutated ras gene. ras oncogenes activated through alterations in codon 12 which encode p21 molecules with impaired GTPase activity, or in codon 59 which produce p21 molecules that release bound guanine nucleotide faster, or in codon 61 which produce p21 having impaired GTPase activity and altered nucleotide release properties, are all able to induce the metastatic phenotype. Leucine-61-activated oncogenes with an additional mutation in codons 116, 117 or 119, resulting in a reduced affinity for guanine nucleotides, are also capable of inducing metastatic behavior. These data indicate that ras genes which are capable of transforming are also capable of inducing the full metastatic phenotype in NIH-3T3 cells. This suggests that both phenotypes are induced through an increase in p21-GTP concentration in ras-transformed cells. This established model for ras-mediated transformation can also explain the qualitative and quantitative regulation of metastatic behavior by ras.

Cotransfection of plasmids with ras and myc oncogenes to diploid cells derived from rodent fetuses: alteration of neoplastic transformation frequency depending on the gestation period

To analyze the mechanism of neoplastic transformation of rodent diploid cells by ras and myc oncogenes, human EJ c-Ha-ras and mouse c-myc second and third exons promoted by SV40 promoter were connected to pSV2neo and pSV2gpt, respectively. Mouse and rat primary fetal cells cotransfected with both genes formed transformed and nontransformed colonies in a medium containing G418 and mycophenolic acid (MPA). The proportion of transformed colonies in the total G418/MPA-resistant colonies decreased dependent on the stage of the gestation period of rat fetuses from which primary cells had been obtained. Analysis of randomly isolated colonies showed that the transformed colonies had a high copy number and high amount of expression of the introduced genes, were anchorage independent, and were tumorigenic in nude mice. On the other hand, the nontransformed colonies had a low copy number, low amount of expression, and no tumorigenicity. This contrast indicated not only that the activated Ha-ras and myc oncogenes had been integrated, but also that the amplification or overexpression (or both) of these genes was required for the rodent diploid cells to be transformed. We conclude that early-stage rat fetal cells might have endogenous factors that promote cell transformation. Alternatively, late-stage cells might have factors that suppress cell transformation by activated Ha-ras and myc oncogenes.

Free radicals and the regulation of mammalian cell proliferation

The question of whether free radicals or free radical-related species play a role in the modulation of mammalian cell proliferation is examined. Although a positive role for free radicals as specific components of mitogenic pathways is not apparent it is clear that certain free radical-derived species can have a significant modulatory influence on components of major growth signal transduction mechanisms. Free radical-derived species are also involved in the production of prostaglandins which themselves can modulate cell growth. Free radicals themselves appear to have a down regulatory effect on cell proliferation inasmuch as protection from oxidative stress enhances cell proliferation. On the other hand, in certain cases low levels of active oxygen species can enhance cell proliferation.

Human KRAS oncogene expression in meningioma

Expression of 16 oncogenes was investigated in a series of human meningiomas showing a normal chromosome complement or the characteristic monosomy 22 but no structural aberrations detectable by banding analysis. By dot hybridization, the only expressed sequence detected was KRAS. The expression was elevated approximately 6--8-fold in comparison to matrix tissue (meninges) and to fibroblasts of the corresponding patient. Northern blot analysis displayed the typical banding pattern and an 8--10-fold overexpression. DNA analysis did not reveal gene amplification or major rearrangements in the KRAS gene structure.

Immunocytochemical demonstration of p21ras in normal and transitional cell carcinoma urothelium

Activation and/or overexpression of the protein product of the ras gene family (p21ras) has been implicated in the development of various cancers, including bladder carcinoma. We have used the anti-p21ras monoclonal antibody, RAP-5, to assess the level and pattern of expression in formalin-fixed, paraffin-embedded tissue sections of both normal and malignant urothelium. All 14 random normal bladder biopsies and 67 of 68 transitional cell carcinomas of the urinary bladder were positively stained with the RAP-5 antibody. In normal urothelium, p21ras staining tended to be localized to the superficial cell layer. With increasing histological grade and/or depth of invasion of the tumour, a greater proportion of tissue sections demonstrated a staining pattern which was more uniform with respect to the different epithelial cell types. Serially diluting the primary antibody did not reveal any significant differences in the staining patterns observed. Despite the change in staining pattern with increasing grade, these results suggest that p21ras expression by itself is not a useful indicator of the malignant phenotype.

Crystallization of human c-H-ras oncogene products

There is compelling evidence that cancer develops as a consequence of genetic changes (probably multiple) in some members of a selected set of cellular genes. DNA isolated from a variety of tumors, but not normal tissues, possesses the ability to malignantly transform non-tumorigenic cells. Many oncogenes responsible for such transformation have been isolated from transformed cell lines and animal and human tumors induced spontaneously, by virus, by chemical, or by radiation. The most commonly found transforming genes isolated from human tumor cells by DNA transfection assay are the ras gene family (c-H-ras, c-K-ras and N-ras). We report crystallization of several human c-H-ras oncogene proteins.

Critical amino acids of p21 protein are located within beta-turns: further evaluation

It has been shown that malignant activation of ras proto-oncogenes was mediated by point mutations which resulted in the single amino acid conversions at positions 12, 13 or 61 of the ras gene products (p21 proteins). By analyzing randomly mutated ras genes, it has been demonstrated that amino acid substitutions at residues 12, 13, 59 and 63 activated p21. Furthermore, it has been shown that residues 16, 116 and 119 in p21 played critical roles in the guanine nucleotide binding and, consequently, the ability of the protein to induce changes characteristic of cellular transformation. By using the protein conformational prediction method of Chou and Fasman, the present work predicts that these critical amino acids, except glutamic acid at position 63, are located within beta-turns. The major "hot spots" for ras activation are codons 12 and 61. The author has predicted in an earlier paper that the single amino acid conversions at positions 12 and 61 would occur at beta-turn conformation consisting of residues 10-13 and 58-61, respectively. In the present study, probabilities of beta-turn occurrence at residues 10-13 or 58-61 of the p21 proteins encoded by various ras genes are compared. The probability for the normal p21 containing glycine as residue 12 is greatest, and the cancer-associated variants show less probabilities. The single amino acid substitutions at position 61 do not cause so decreased probabilities of beta-turn potential at residues 58-61, except the replacement by histidine. Histidine at position 61 is not predicted as occurring within a beta-turn.(ABSTRACT TRUNCATED AT 250 WORDS)

ras proteins enhance the phosphorylation of a 38 kDa protein (p38) in rat liver plasma membrane

Phosphorylation of a 38 kDa protein (p38) present in rat liver plasma membrane has been shown for the first time to be enhanced by ras proteins. This increase in phosphorylation is about 3-16-fold depending on the incubation time and the type of ras protein used. Acid treatment removes phosphate from this protein suggesting that the phosphorylation involves phosphoramidate derivatives of basic amino acids. Experiments carried out in the presence of diethylpyrocarbonate suggest that the phosphorylation occurs on (a) histidine residue(s). It is probable that the function of p38 in the cell is modulated by ras proteins through phosphorylation. The significance of phosphorylation of p38 in terms of malignant transformation is presently known.

Pancreatic neoplasia induced by ras expression in acinar cells of transgenic mice

Expression of an activated human c-H-ras oncogene under control of rat elastase I regulating elements leads to neoplasia of the fetal exocrine pancreas. In most transgenic mice bearing this gene construct, massive tumors involving all the pancreatic acinar cells develop within a few days of pancreatic differentiation. Expression of the normal c-H-ras proto-oncogene in acinar cells leads to more subtle anomalies, but no tumors develop. Thus modest amounts of the mutant ras proteins are sufficient, in an otherwise normal genetic background, to lead to neoplastic transformation of differentiating pancreatic acinar cells. In contrast, a comparable elastase-myc construct produces no pancreatic tumors in transgenic mice.

The c-Ha-ras oncogene and a tumor promoter activate the polyoma virus enhancer

A c-Ha-ras oncogene, to a lesser extent the c-Ha-ras proto-oncogene, and the tumor promoter 12-O-tetradecanoylphorbol-13-acetate activate the inactive polyoma virus (Py) enhancer in a myeloma cell line and the partially active Py enhancer in NIH 3T3 fibroblasts, but have no effect on the active Py enhancer in LMTK- fibroblasts. In addition, c-Ha-ras can stimulate the inactive Py enhancer in embryonal carcinoma F9 cells. c-Ha-ras activation in embryonal carcinoma cells does not appear to involve reversal of "E1A-like" inhibition of the enhancer. We suggest that modulation of cellular enhancer activity could play a key role in tumorigenesis by oncogenes.

Structure of the human and murine R-ras genes, novel genes closely related to ras proto-oncogenes

The human R-ras gene was isolated by low-stringency hybridization with a v-H-ras probe. The predicted 218 amino acid R-ras protein has an amino-terminal extension of 26 residues compared with H-ras p21, and shows 55% amino acid identity; conserved domains include the p21 GTP-binding site and the carboxy-terminal membrane localization sequence. R-ras has at least six exons, with the position of the first intron conserved relative to the Drosophila ras64B and Dictyostelium ras genes; there is no similarity in the exon-intron structure of the R-ras gene and of the mammalian H-, K-, and N-ras proto-oncogenes. Cloned mouse R-ras cDNAs exhibit 88% nucleotide and 94.5% predicted amino acid identity to human R-ras. Human R-ras was localized to chromosome 19, a site different from ras p21 genes. Mouse R-ras is syntenic with c-H-ras on chromosome 7.

The molecular genetics of cancer

The search for genetic damage in neoplastic cells now occupies a central place in cancer research. Diverse examples of such damage are in hand, and they in turn hint at biochemical explanations for neoplastic growth. The way may be open to solve the riddles of how normal cells govern their replication and why cancer cells do not.

Calcium, cyclic AMP and protein kinase C--partners in mitogenesis

Evidence is steadily mounting that the proto-oncogenes, whose products organize and start the programs that drive normal eukaryotic cells through their chromosome replication/mitosis cycles, are transiently stimulated by sequential signals from a multi-purpose, receptor-operated mechanism (consisting of internal surges of Ca2+ and bursts of protein kinase C activity resulting from phosphatidylinositol 4,5-bisphosphate breakdown and the opening of membrane Ca2+ channels induced by receptor-associated tyrosine-protein kinase activity) and bursts of cyclic AMP-dependent kinase activity. The bypassing or subversion of the receptor-operated Ca2+/phospholipid breakdown/protein kinase C signalling mechanism is probably the basis of the freeing of cell proliferation from external controls that characterizes all neoplastic transformations.

A repetitive sequence element 3' of the human c-Ha-ras1 gene has enhancer activity

Efficient expression of the human c-Ha-ras1 gene requires sequences 3' of those specifying the polyadenylation of its transcripts. These sequences can stimulate the expression of heterologous genes in a manner largely independent of position and orientation, arguing that they possess a transcriptional enhancing activity that regulates the c-Ha-ras1 promoter. As this element is associated with a repetitive domain that is highly polymorphic, it is possible that the activity of this enhancer is variable within the human population.

The oncogenic activation of human p21ras by a novel mechanism

Single amino acid changes were introduced into normal (non-oncogenic) and activated forms of the human H-ras protein at a position (residue 116) proposed on structural grounds to represent a contact site with guanine nucleotides. Substitutions at this site could significantly reduce the ability of both forms to bind and hydrolyze guanosine 5'-triphosphate; these substitutions, however, did not necessarily diminish the transforming capacity of activated derivatives. One substitution that severely impairs these functions activated the transforming potential of the otherwise normal polypeptide.