Mouse cells contain two distinct ras gene mRNA species that can be translated into a p21 onc protein

40 Years of RAS-A Historic Overview

It has been over forty years since the isolation of the first human oncogene (HRAS), a crucial milestone in cancer research made possible through the combined efforts of a few selected research groups at the beginning of the 1980s. Those initial discoveries led to a quantitative leap in our understanding of cancer biology and set up the onset of the field of molecular oncology. The following four decades of RAS research have produced a huge pool of new knowledge about the RAS family of small GTPases, including how they regulate signaling pathways controlling many cellular physiological processes, or how oncogenic mutations trigger pathological conditions, including developmental syndromes or many cancer types. However, despite the extensive body of available basic knowledge, specific effective treatments for RAS-driven cancers are still lacking. Hopefully, recent advances involving the discovery of novel pockets on the RAS surface as well as highly specific small-molecule inhibitors able to block its interaction with effectors and/or activators may lead to the development of new, effective treatments for cancer. This review intends to provide a quick, summarized historical overview of the main milestones in RAS research spanning from the initial discovery of the viral RAS oncogenes in rodent tumors to the latest attempts at targeting RAS oncogenes in various human cancers.

Targeting Ras-RAF-ERK and its interactive pathways as a novel therapy for malignant gliomas

Malignant gliomas are the most common and the deadliest brain malignancies in adults. Despite the lack of a complete understanding of the biology of these tumors, significant advances have been made in the past decades. One of the key discoveries made in the area of malignant gliomas is that these tumors can be induced and maintained by aberrant signaling networks. In this context, the Ras pathway has been extensively exploited, from both basic and translational perspectives. Although somatic oncogenic mutations of Ras genes are frequent in several cancer types, early investigations on gliomas revealed disappointing facts that the Ras mutations are nearly absent in malignant gliomas and that the BRAF mutations are present in a very small percentage of gliomas. Therefore, the observed deregulation of the Ras-RAF-ERK signaling pathway in gliomas is attributed to its upstream positive regulators, including, EGFR and PDGFR known to be highly active in the majority of malignant gliomas. In contrast to the initial negative results on the somatic mutations of H-Ras, K-Ras and BRAF, recent breakthrough studies on pediatric low-grade astrocytomas uncovered genetic alterations of the BRAF gene involving copy number gains and rearrangements. The 7q34 rearrangements result in a novel in-frame KIAA1549:BRAF fusion gene that possesses constitutive BRAF kinase activity resembling oncogenic BRAF (V600E). In light of the earlier findings and recent breakthroughs, this review summarizes our current understanding of the Ras-RAF-ERK signaling pathway in gliomas and the outcome of preclinical and clinical studies that evaluated the efficacy of Ras-targeted therapy in malignant gliomas.

Ras oncogenes: split personalities

Extensive research on the Ras proteins and their functions in cell physiology over the past 30 years has led to numerous insights that have revealed the involvement of Ras not only in tumorigenesis but also in many developmental disorders. Despite great strides in our understanding of the molecular and cellular mechanisms of action of the Ras proteins, the expanding roster of their downstream effectors and the complexity of the signalling cascades that they regulate indicate that much remains to be learnt.

Influence of calorie restriction on oncogene expression and DNA synthesis during liver regeneration

Controlling calorie intake (CCI) extends healthful life-span by a mechanism that may involve reduced rates of cell division without detriment to inducible cellular responses. To test whether inducible cellular proliferation is preserved by CCI and whether the mRNA expression levels of oncogenes activated by cell division can be reduced by CCI, we evaluated the effect of dietary energy on the hepatocellular proliferative burst and on oncogene and growth factor mRNA expression induced by partial hepatectomy. Eighty Fischer 344 rats were separated into two dietary groups and were fed semipurified diets for 10 weeks that differed only in calories by 40%. Mean hepatic levels of [3H]thymidine incorporation were greater among CCI animals at 18, 24, 28, and 36 hr after partial hepatectomy. The expression of c-fos and c-Ki-ras mRNAs, activated during hepatic regeneration, was reduced by CCI. Peak expression of c-fos among ad libitum fed controls to levels 4-6 times greater than prehepatectomy levels was not detected among CCI animals. Protracted elevated expression of c-Ki-ras among ad libitum fed animals was foreshortened by CCI. These findings demonstrate that inducible cellular proliferative responses are preserved by CCI and that the mRNA expression levels of c-fos and c-Ki-ras activated during cell division are reduced by controlling dietary energy. Preserved inducible cellular responses and lowered oncogene expression during cell division may be attributes of the healthful protective effect of CCI.

Induction of c-Ha-ras gene expression by double-stranded RNA and interferon requirement

The addition of double-stranded RNA (dsRNA) to NIH 3T3 cells led to an increase in the RNA levels of c-Ha-ras. The double-stranded configuration was required for the increase in c-Ha-ras mRNA levels, as heat-denatured dsRNA and single-stranded RNA did not have any effect. Nuclear run-on transcription experiments indicated that the increase in c-Ha-ras mRNA levels stimulated by dsRNA was due to transcriptional activation of the gene. The induction of c-Ha-ras gene expression by dsRNA was inhibited by anti-beta interferon antibodies, suggesting that interferon might mediate the induction.

Induction of c-Ha-ras gene expression by double-stranded RNA and interferon requirement

The addition of double-stranded RNA (dsRNA) to NIH 3T3 cells led to an increase in the RNA levels of c-Ha-ras. The double-stranded configuration was required for the increase in c-Ha-ras mRNA levels, as heat-denatured dsRNA and single-stranded RNA did not have any effect. Nuclear run-on transcription experiments indicated that the increase in c-Ha-ras mRNA levels stimulated by dsRNA was due to transcriptional activation of the gene. The induction of c-Ha-ras gene expression by dsRNA was inhibited by anti-beta interferon antibodies, suggesting that interferon might mediate the induction.

Transcriptional activation of cKi-ras proto-oncogene resulting from retroviral promoter insertion

Enhanced expression of the cKi-ras proto-oncogene in a bone marrow-derived mouse cell line, 416B, has been shown to be associated with the integration of Friend viral DNA into the cellular gene. Here we report the results of experiments designed to clarify the molecular mechanism responsible for the cKi-ras overexpression. Based on primer extension analyses and DNA sequencing of cKi-ras cDNA clones, we have obtained evidence that the 416B cells contain viral-host chimaeric transcripts that initiate within the 3' long terminal repeat (LTR) of the integrated provirus. Processing of the transcripts from the rearranged cKi-ras gene includes an unexpected splicing event associated with the fortuitous creation of a cryptic donor splice site at the junction between the proviral and cellular DNA sequences. These data demonstrate that enhanced cKi-ras expression in the 416B cells results from a retroviral promoter insertion mechanism of transcriptional activation.

Amplification and rearrangement of the Kirsten ras oncogene in virus-transformed BALB/c 3T3 cells during malignant tumor progression

Analyses of the cellular and viral Kirsten ras genes (c-Ki-ras and v-Ki-ras, respectively) during malignant tumor progression were performed by using Kirsten murine sarcoma virus-transformed BALB/c 3T3 cells that harbor a replication-defective provirus. After injection into athymic nude mice by four different routes, primary tumors and secondary lung metastases were isolated, adapted to in vitro growth, and analyzed for DNA levels and mRNA expression of both genes for comparison with the originally injected transformed cells and untransformed 3T3 cells. For all tumors (primary or secondary), the v-Ki-ras gene was amplified and v-Ki-ras mRNA expression was highly elevated above that observed in the original transformed cell population. In two of five lung metastases from the i.v. and footpad injection routes, rearranged Ki-ras DNA sequences were observed. Micrometastases from the s.c. route of injection did not display these alterations. Injection of footpad lung tumor cells with rearrangements into a second group of animals led to multiple lung metastases with even further rearrangements correlating with more effective lung colonization/growth ability (overt lung tumors in five of eight animals less than 20 days after injection). However, reinjection of an i.v. lung tumor with rearranged Ki-ras led to no further rearrangements in the lung microfoci tumors isolated greater than 40 days after injection. These data suggest (i) the significance of amplification and elevated expression of v-Ki-ras in tumor formation, (ii) correlation of this amplification with more effective tumor progression, and (iii) the selective advantage that cells with Ki-ras DNA sequence additions have in the formation of overt lung tumors.

Expression of H-ras correlates with metastatic potential: evidence for direct regulation of the metastatic phenotype in 10T1/2 and NIH 3T3 cells

Using three independent approaches, we studied the effects of H-ras on metastasis formation. Analysis of five in vitro-ras-transfected 10T1/2 clones with either flat or refractile morphologies revealed a relationship between metastatic potential, H-ras expression, and anchorage-independent growth. Four metastatic variants derived from a poorly metastatic, low-H-ras-expressing line all expressed high levels of H-ras RNA and grew efficiently in soft agar. Activation of H-ras expression in the metastatic tumors had occurred through amplification and rearrangement of H-ras sequences. In addition, preinduction of p21 synthesis in NIH 3T3 line 433, which contains v-H-ras under transcriptional control of the glucocorticoid-sensitive mouse mammary tumor virus long terminal repeat, significantly increased metastatic efficiency. Glucocorticoid treatment of normal or pEJ-transformed NIH 3T3 cells did not affect metastatic potential. These data reveal a direct relationship between ras expression and metastasis formation and suggest that metastatic and transformed phenotypes may be coregulated in ras-transformed 10T1/2 and NIH 3T3 cells.

Expression of H-ras correlates with metastatic potential: evidence for direct regulation of the metastatic phenotype in 10T1/2 and NIH 3T3 cells

Using three independent approaches, we studied the effects of H-ras on metastasis formation. Analysis of five in vitro-ras-transfected 10T1/2 clones with either flat or refractile morphologies revealed a relationship between metastatic potential, H-ras expression, and anchorage-independent growth. Four metastatic variants derived from a poorly metastatic, low-H-ras-expressing line all expressed high levels of H-ras RNA and grew efficiently in soft agar. Activation of H-ras expression in the metastatic tumors had occurred through amplification and rearrangement of H-ras sequences. In addition, preinduction of p21 synthesis in NIH 3T3 line 433, which contains v-H-ras under transcriptional control of the glucocorticoid-sensitive mouse mammary tumor virus long terminal repeat, significantly increased metastatic efficiency. Glucocorticoid treatment of normal or pEJ-transformed NIH 3T3 cells did not affect metastatic potential. These data reveal a direct relationship between ras expression and metastasis formation and suggest that metastatic and transformed phenotypes may be coregulated in ras-transformed 10T1/2 and NIH 3T3 cells.

Transforming activity of DNA fragments from normal human lymphocytes results from spontaneous activation of a c-Ha-ras1 gene

An activated human Ha-ras gene was present in a secondary NIH 3T3 transformant isolated after serial transfection of originally low-molecular-weight DNA fragments from normal human cells. This gene appeared to have acquired its transforming properties by a spontaneous mutation in codon 12 by substitution of a deoxythymidine residue for a deoxyguanosine residue. DNA rearrangements in the flanking sequences of the transferred Ha-ras gene were not involved in the activation of the protooncogene.

Harvey ras genes transform without mutant codons, apparently activated by truncation of a 5' exon (exon -1)

The hypothesis is tested that the ras gene of Harvey sarcoma virus (Ha-SV) and the proto-ras DNAs from certain tumor cells derive transforming function from specific codons in which they differ from normal proto-ras genes. Molecularly cloned Harvey proviral vectors carrying viral ras, normal rat proto-ras, and recombinant ras genes in which the virus-specific ras codons 12 and 59 were replaced by proto-ras equivalents each transformed aneuploid mouse 3T3 cells after latent periods that ranged from 4 to 10 days. Viruses with or without virus-specific ras codons all transformed diploid rat cells in 3-5 days equally well. However, in the absence of virus replication, mutant codons were beneficial for transforming function. Deletion of non-ras regions of Ha-SV did not affect transforming function. We conclude that specific ras codons are not necessary for transforming function. Comparisons of the ras sequences of Ha-SV, BALB SV, and Rasheed SV with sequences of proto-ras genes from rat and man revealed an upstream proto-ras exon, termed exon -1. The 3' end of this exon is present in all three viruses and in a ras pseudogene of the rat. Since ras genes transform without mutation and since exon -1 is truncated in viral ras genes and all transforming proto-ras DNAs of the Harvey and the Kirsten ras family, we propose that ras genes are activated by truncation of exon -1 either via viral transduction or artificially via cloning and transfection. The proposal implies that untruncated proto-ras genes with point mutations may not be cellular cancer genes.

Enhanced c-Ki-ras expression associated with Friend virus integration in a bone marrow-derived mouse cell line

We have investigated the molecular basis for a 25- to 30-fold overexpression of the c-Ki-ras oncogene in a mouse bone marrow-derived, early myeloid cell line, 416B. Southern blot hybridizations revealed that the 416B cells contain a rearranged c-Ki-ras gene in addition to an apparently normal gene. Molecular cloning and DNA sequence analyses demonstrated that the rearrangement involves the insertion of a 3.5-kilobase-pair segment of Friend virus that includes the envelope gene (env) and 3' long terminal repeat. The Friend provirus is positioned between a 5' nontranslated exon (exon phi) and the first coding exon (exon 1) of the c-Ki-ras gene in the same transcriptional orientation. Results of RNA blot analyses indicate that transcription from the rearranged gene initiates at a promoter that excludes sequences in exon phi. The data support the hypothesis that enhanced c-Ki-ras expression in the 416B cells results from integration of a Friend provirus within this gene.

Expression of c-Ki-ras, c-Ha-ras, and c-myc in specific cell types during hepatocarcinogenesis

We examined the expression of six proto-oncogenes in (i) whole rat liver and isolated liver cell populations during the course of hepatocarcinogenesis induced by a choline-deficient diet containing 0.1% ethionine and (ii) fetal rat liver at different stages of development. The abundance of c-Ki-ras, c-Ha-ras, and c-myc transcripts in polysomal polyadenylated RNA from liver cells increased by 2 weeks after the start of the carcinogenic diet. c-Ki-ras and c-myc expression remained elevated during the 35 weeks of the diet, whereas c-Ha-ras transcripts increased transiently. A primary tumor sampled at 35 weeks after the carcinogenic diet was started contained high levels of both c-Ki-ras and c-myc RNA. The abundance of c-src transcripts was unchanged throughout carcinogenesis; c-abl and c-mos transcripts were not detected in either preneoplastic or neoplastic livers. To determine which cell types within the liver contained proto-oncogene transcripts, we isolated hepatocytes, oval cells, and bile duct cells from normal and preneoplastic livers. The results indicate that proto-oncogenes are expressed differentially in these cell types during hepatocarcinogenesis and that the expression of c-Ki-ras and c-myc is high in oval cells throughout carcinogenesis. In developing livers, c-Ki-ras, c-Ha-ras, and c-myc transcript levels were high at 17 days of gestation but reached the low values characteristic of adult rat livers between 20 days of gestation and 3 days after birth.

Expression of c-Ki-ras, c-Ha-ras, and c-myc in specific cell types during hepatocarcinogenesis

We examined the expression of six proto-oncogenes in (i) whole rat liver and isolated liver cell populations during the course of hepatocarcinogenesis induced by a choline-deficient diet containing 0.1% ethionine and (ii) fetal rat liver at different stages of development. The abundance of c-Ki-ras, c-Ha-ras, and c-myc transcripts in polysomal polyadenylated RNA from liver cells increased by 2 weeks after the start of the carcinogenic diet. c-Ki-ras and c-myc expression remained elevated during the 35 weeks of the diet, whereas c-Ha-ras transcripts increased transiently. A primary tumor sampled at 35 weeks after the carcinogenic diet was started contained high levels of both c-Ki-ras and c-myc RNA. The abundance of c-src transcripts was unchanged throughout carcinogenesis; c-abl and c-mos transcripts were not detected in either preneoplastic or neoplastic livers. To determine which cell types within the liver contained proto-oncogene transcripts, we isolated hepatocytes, oval cells, and bile duct cells from normal and preneoplastic livers. The results indicate that proto-oncogenes are expressed differentially in these cell types during hepatocarcinogenesis and that the expression of c-Ki-ras and c-myc is high in oval cells throughout carcinogenesis. In developing livers, c-Ki-ras, c-Ha-ras, and c-myc transcript levels were high at 17 days of gestation but reached the low values characteristic of adult rat livers between 20 days of gestation and 3 days after birth.

Expression and characterization of ras mRNAs from Saccharomyces cerevisiae

The cellular homologs of the Harvey and Kirsten murine sarcoma virus oncogenes comprise a multigene family, ras, that displays striking evolutionary conservation. We recently reported [DeFeo-Jones et al., Nature (London) 306:707-709, 1983] the cloning of two ras homologs from the yeast Saccharomyces cerevisiae. The nucleotide sequences of these genes predict polypeptides that show remarkable homology to p21, the mammalian ras gene product. We have also found proteins in yeast lysates with serological cross-reactivity to p21 (Papageorge et al., Mol. Cell. Biol. 4:23-29, 1984). In this work, we explored the relationship between the immunoprecipitated proteins and the yeast ras genes. We show that both ras genes are expressed in the wild-type cell. Furthermore, we demonstrate by in vitro translation of hybrid-selected RASsc1 mRNA and immunoprecipitation of the translation products that the cloned RASsc1 gene encodes the proteins immunoprecipitated from yeast lysates by anti-p21 monoclonal antibody. Finally, we used anti-p21 monoclonal antibodies to detect a guanine nucleotide binding activity in yeast lysates. The structural and biochemical homologies between ras gene products of S. cerevisiae and mammalian cells suggest that information obtained by genetic analysis of ras function in a lower eucaryote should be applicable to higher organisms as well.

Regulated transcription of c-Ki-ras and c-myc during compensatory growth of rat liver

We examined the transcription of six cellular oncogenes during the process of compensatory growth in rat liver after partial hepatectomy. We have previously reported that transcripts of c-rasH are elevated during regenerative growth of the liver. We now report that transcripts of c-rasK and c-myc genes are significantly elevated after partial hepatectomy, whereas transcripts of c-abl and c-src are essentially unchanged and transcripts of c-mos are undetectable in either normal or regenerating rat liver. In liver regeneration after partial hepatectomy or chemical injury, changes in c-myc transcripts occur before DNA synthesis. The elevation of c-myc and c-ras transcripts is sequential in that highest levels of c-myc transcripts were detected 12 to 18 h after partial hepatectomy, whereas the levels of c-rasH and c-rasK were maximal by 36 to 48 h. Transcripts of all three activated oncogenes returned to their basal levels by 96 h.

Expression and characterization of ras mRNAs from Saccharomyces cerevisiae

The cellular homologs of the Harvey and Kirsten murine sarcoma virus oncogenes comprise a multigene family, ras, that displays striking evolutionary conservation. We recently reported [DeFeo-Jones et al., Nature (London) 306:707-709, 1983] the cloning of two ras homologs from the yeast Saccharomyces cerevisiae. The nucleotide sequences of these genes predict polypeptides that show remarkable homology to p21, the mammalian ras gene product. We have also found proteins in yeast lysates with serological cross-reactivity to p21 (Papageorge et al., Mol. Cell. Biol. 4:23-29, 1984). In this work, we explored the relationship between the immunoprecipitated proteins and the yeast ras genes. We show that both ras genes are expressed in the wild-type cell. Furthermore, we demonstrate by in vitro translation of hybrid-selected RASsc1 mRNA and immunoprecipitation of the translation products that the cloned RASsc1 gene encodes the proteins immunoprecipitated from yeast lysates by anti-p21 monoclonal antibody. Finally, we used anti-p21 monoclonal antibodies to detect a guanine nucleotide binding activity in yeast lysates. The structural and biochemical homologies between ras gene products of S. cerevisiae and mammalian cells suggest that information obtained by genetic analysis of ras function in a lower eucaryote should be applicable to higher organisms as well.

Regulated transcription of c-Ki-ras and c-myc during compensatory growth of rat liver

We examined the transcription of six cellular oncogenes during the process of compensatory growth in rat liver after partial hepatectomy. We have previously reported that transcripts of c-rasH are elevated during regenerative growth of the liver. We now report that transcripts of c-rasK and c-myc genes are significantly elevated after partial hepatectomy, whereas transcripts of c-abl and c-src are essentially unchanged and transcripts of c-mos are undetectable in either normal or regenerating rat liver. In liver regeneration after partial hepatectomy or chemical injury, changes in c-myc transcripts occur before DNA synthesis. The elevation of c-myc and c-ras transcripts is sequential in that highest levels of c-myc transcripts were detected 12 to 18 h after partial hepatectomy, whereas the levels of c-rasH and c-rasK were maximal by 36 to 48 h. Transcripts of all three activated oncogenes returned to their basal levels by 96 h.

Amplified DNA in Y1 mouse adrenal tumor cells: isolation of cDNAs complementary to an amplified c-Ki-ras gene and localization of homologous sequences to mouse chromosome 6

We have isolated cDNA clones complementary to a c-Ki-ras cellular oncogene that is amplified in Y1 mouse adrenal tumor cells, with the amplified sequences located on double-minute chromatin bodies (DMs) and homogeneously staining chromosomal regions (HSRs). Characterization of the cDNAs included the isolation of corresponding genomic clones, Northern blot analysis of RNA, and DNA sequence analysis. Our studies demonstrate that the c-Ki-ras gene amplified in the Y1 cells is homologous to the human c-Ki-ras2 gene. We have also obtained evidence that, in addition to c-Ki-ras, at least one other transcription unit has been amplified in the mouse adrenal tumor cells. Moreover, by Southern blot analysis of Chinese hamster-mouse somatic cell hybrids, we have determined that the amplified DNA sequences associated with DMs and HSRs, including the c-Ki-ras gene, are present in normal mouse cells on chromosome 6.

Expression of Kirsten murine sarcoma virus in transformed nonproducer and revertant NIH/3T3 cells: evidence for cell-mediated resistance to a viral oncogene in phenotypic reversion

Expression of the provirus in a clonally related series of Kirsten murine sarcoma virus-transformed NIH/3T3 nonproducer cell lines was examined at both the transcriptional and translational levels. All cells expressed high levels of genome-sized viral RNA with little variation between cell lines despite differences in provirus integration site and copy number. Expression of K-ras RNA was estimated to be at least 10- to 20-fold higher than that of the mouse cellular homolog of the viral transforming gene. Levels of the virus-coded transforming protein, p21, were similarly elevated, with little variation between nonproducer cells. In two revertant cell lines containing a normal provirus and a rescuable transforming gene, no impairment in expression at either the transcriptional or translational level was found. After superinfection with Kirsten murine sarcoma virus, one revertant became more tumorigenic, whereas the other remained nontumorigenic. These results show that cell transformation by Kirsten murine sarcoma virus is invariably associated with elevated expression of the virus-coded oncogene and that one of the revertants is resistant to the action of the viral transforming gene.

Saccharomyces cerevisiae synthesizes proteins related to the p21 gene product of ras genes found in mammals

A family of normal vertebrate genes and oncogenes has been called the ras gene family. The name ras was assigned to this gene family based on the species of origin of the viral oncogenes of the rat-derived Harvey and Kirsten murine sarcoma viruses. There are now three known functional members of the ras gene family, and genes homologous to ras genes have been detected in the DNA of a wide variety of mammals and in Drosophila melanogaster. Prior experiments have detected proteins coded for by ras genes in a large number of normal cells, cell lines, and tumors. We report here the detection of ras-related proteins in D. melanogaster, a result predicted by the earlier detection of ras-related genes in the Drosophila genome. We also report for the first time the detection of ras-related proteins in a single-cell eucaryocyte, Saccharomyces cerevisiae. These proteins, approximately 30K in size, are recognized by both a monoclonal antibody which binds to the p21 coded for by mammalian ras genes and a polyclonal rat serum made by transplanting a v-Ha-ras-induced tumor in Osborne-Mendel rats. The p21 of v-Ha-ras and the 30K proteins from S. cerevisiae share methionine-labeled peptides as detected by two-dimensional tryptic peptide maps. The results indicate that S. cerevisiae synthesizes ras-related proteins. A genetic analysis of the function of these proteins for yeast cells may now be possible.

Saccharomyces cerevisiae synthesizes proteins related to the p21 gene product of ras genes found in mammals

A family of normal vertebrate genes and oncogenes has been called the ras gene family. The name ras was assigned to this gene family based on the species of origin of the viral oncogenes of the rat-derived Harvey and Kirsten murine sarcoma viruses. There are now three known functional members of the ras gene family, and genes homologous to ras genes have been detected in the DNA of a wide variety of mammals and in Drosophila melanogaster. Prior experiments have detected proteins coded for by ras genes in a large number of normal cells, cell lines, and tumors. We report here the detection of ras-related proteins in D. melanogaster, a result predicted by the earlier detection of ras-related genes in the Drosophila genome. We also report for the first time the detection of ras-related proteins in a single-cell eucaryocyte, Saccharomyces cerevisiae. These proteins, approximately 30K in size, are recognized by both a monoclonal antibody which binds to the p21 coded for by mammalian ras genes and a polyclonal rat serum made by transplanting a v-Ha-ras-induced tumor in Osborne-Mendel rats. The p21 of v-Ha-ras and the 30K proteins from S. cerevisiae share methionine-labeled peptides as detected by two-dimensional tryptic peptide maps. The results indicate that S. cerevisiae synthesizes ras-related proteins. A genetic analysis of the function of these proteins for yeast cells may now be possible.

Transcription of c-onc genes c-rasKi and c-fms during mouse development

We investigated the expression of cellular sequences c-rasKi and c-fms, which are homologous to the oncogenes of Kirsten rat sarcoma virus and the McDonough strain of feline sarcoma virus, during murine development and in a variety of mouse tissues. The c-rasKi gene was found to be transcribed into two mRNA species of approximately 2.0 and 4.4 kilobases, whereas a single c-fms-related transcript of approximately 3.7 kilobases was identified. The c-rasKi gene appeared to be expressed ubiquitously, since similar levels of transcripts were observed in embryos, fetuses, extraembryonal structures, and a variety of postnatal tissues. In contrast, significant expression of c-fms was found to be confined to the placenta and extraembryonal membranes (i.e., combined yolk sac and amnion). The concentration of c-fms transcripts in the placenta increased approximately 15-fold (relative to day-7 to day-9 conceptuses) during development before reaching a plateau at day 14 to 15 of gestation. The time course of cfms expression in the extraembryonal membranes appeared to parallel the stage-specific pattern observed in the placenta. The level of c-fms transcripts in the extraembryonal tissues reached a level which was approximately 20- to 50-fold greater than that in the fetus. These findings suggest that the c-fms gene product may play a role in differentiation of extraembryonal structures or in transport processes occurring in these tissues. Our results indicate that the c-onc genes analyzed in the present study exert essentially different functions during mouse development.

Transcription of c-onc genes c-rasKi and c-fms during mouse development

We investigated the expression of cellular sequences c-rasKi and c-fms, which are homologous to the oncogenes of Kirsten rat sarcoma virus and the McDonough strain of feline sarcoma virus, during murine development and in a variety of mouse tissues. The c-rasKi gene was found to be transcribed into two mRNA species of approximately 2.0 and 4.4 kilobases, whereas a single c-fms-related transcript of approximately 3.7 kilobases was identified. The c-rasKi gene appeared to be expressed ubiquitously, since similar levels of transcripts were observed in embryos, fetuses, extraembryonal structures, and a variety of postnatal tissues. In contrast, significant expression of c-fms was found to be confined to the placenta and extraembryonal membranes (i.e., combined yolk sac and amnion). The concentration of c-fms transcripts in the placenta increased approximately 15-fold (relative to day-7 to day-9 conceptuses) during development before reaching a plateau at day 14 to 15 of gestation. The time course of cfms expression in the extraembryonal membranes appeared to parallel the stage-specific pattern observed in the placenta. The level of c-fms transcripts in the extraembryonal tissues reached a level which was approximately 20- to 50-fold greater than that in the fetus. These findings suggest that the c-fms gene product may play a role in differentiation of extraembryonal structures or in transport processes occurring in these tissues. Our results indicate that the c-onc genes analyzed in the present study exert essentially different functions during mouse development.

Transcription of mouse mammary tumor virus: identification of a candidate mRNA for the long terminal repeat gene product

We have examined an assortment of preneoplastic and neoplastic mouse mammary tissues for the presence of an mRNA which could encode the putative long terminal repeat gene product of mouse mammary tumor virus. We report here the detection of a novel mouse mammary tumor virus-specific, polyadenylic acid-containing transcript in certain preneoplastic and neoplastic mammary tissue of BALB/c mice. The molecule is 1.6 kilobases in length and contains sequences from the transcriptional leader and the U3 region of the proviral DNA. The upstream terminus of the 3' information lies 75 to 80 nucleotides from the beginning of the long terminal repeat open reading frame, in close proximity to a consensus splice acceptor in the DNA. The transcript was detected in hormonally or chemically induced neoplastic, preneoplastic, and lactating mammary tissue of BALB/c mice, but not in preneoplastic or tumor tissue induced by exogenous viruses in any strain of mice examined. This implies that the RNA we observed is transcribed from an endogenous provirus template.