Mouse cells contain two distinct ras gene mRNA species that can be translated into a p21 onc protein. Mol Cell Biol. 1982;2:1339-1345. [PMID: 6131379 DOI: 10.1128/MCB.2.11.1339]

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.

The RAL signaling network: Cancer and beyond

The RAL proteins RALA and RALB belong to the superfamily of small RAS-like GTPases (guanosine triphosphatases). RAL GTPases function as molecular switches in cells by cycling through GDP- and GTP-bound states, a process which is regulated by several guanine exchange factors (GEFs) and two heterodimeric GTPase activating proteins (GAPs). Since their discovery in the 1980s, RALA and RALB have been established to exert isoform-specific functions in central cellular processes such as exocytosis, endocytosis, actin organization and gene expression. Consequently, it is not surprising that an increasing number of physiological functions are discovered to be controlled by RAL, including neuronal plasticity, immune response, and glucose and lipid homeostasis. The critical importance of RAL GTPases for oncogenic RAS-driven cellular transformation and tumorigenesis still attracts most research interest. Here, RAL proteins are key drivers of cell migration, metastasis, anchorage-independent proliferation, and survival. This chapter provides an overview of normal and pathological functions of RAL GTPases and summarizes the current knowledge on the involvement of RAL in human disease as well as current therapeutic targeting strategies. In particular, molecular mechanisms that specifically control RAL activity and RAL effector usage in different scenarios are outlined, putting a spotlight on the complexity of the RAL GTPase signaling network and the emerging theme of RAS-independent regulation and relevance of RAL.

Effect of KRAS mutation status on efficacy of EGFR monoclonal antibody treatment in colorectal cancer

Colorectal cancer is one of the most common malignant tumors. With the development of economy and the improvement of living standard in China, which have resulted in great changes in lifestyle and eating habits, the incidence of colorectal cancer has increased year by year. Among all treatments currently available, targeted therapy is considered to be the most ideal treatment for metastatic colorectal cancer. KRAS mutation is closely related to the efficacy of targeted therapy for colorectal cancer. Thus, it is important to clarify the KRAS mutation status before targeted therapy is considered. This paper mainly elaborates the effect of KRAS mutation status on the efficacy of epidermal growth factor receptor monoclonal antibody treatment of colorectal cancer with regard to the structure and function of KRAS gene, KRAS mutations and heterogeneity.

KRAS mutation testing in human cancers: The pathologist's role in the era of personalized medicine

A number of studies have shown that although antiepidermal growth factor receptor (EGFR) monoclonal antibodies are effective treatments for metastatic colorectal cancer (mCRC), only patients with wild-type KRAS tumors derive clinical benefit from these therapies. The anti-EGFR monoclonal antibodies panitumumab and cetuximab are approved in the United States for treatment of mCRC refractory to chemotherapy but are not recommended for use in patients with mutations in KRAS codons 12 or 13. Similarly, panitumumab is approved for the treatment of mCRC only in patients with wild-type KRAS in Europe and Canada. It is clear that KRAS mutational analysis will become an important aspect of disease management in patients with mCRC. Consequently, it will be important for pathologists and oncologists to develop and agree on standardized KRAS testing and reporting procedures to ensure optimum patient care. Pathologists will be central to this process because of their crucial role in selecting appropriate tumor specimens for testing, choosing the molecular diagnostic laboratory to be used, assisting in the selection of a suitable KRAS test, and interpreting the results of KRAS mutational analysis. Guidelines for KRAS testing that address these and other important points of consideration have recently been proposed in the United States and the European Union.

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.

Dome formation induced by v-H-ras oncogene in a human choriocarcinoma cell line

To investigate the role of ras genes in trophoblastic cell lineage, we transfected the viral H- or K-ras oncogene into a human choriocarcinoma cell line, CCI, and analysed the biological properties of CCI cells expressing an activated ras oncogene. All v-H-ras-expressing clones distinctively formed the hemispherical domes, which represents an in vitro morphological expression of vectorial transport function and are characteristic of the polarized epithelial cells, but none of v-K-ras-expressing clones and control clones did. Microscopic observation demonstrated that those domes were cavities filled with fluid which accumulated between the cell layer and the surface of culture dish. Scanning electron microscopy revealed that the domes were aggregates of round cells with long numerous microvilli and were morphologically similar to a blastocyst. Furthermore, Na(+)-K(+)-ATPase activity, which is associated with the vectorial fluid transport in transporting epithelial cells, was significantly higher in the v-H-ras-expressing clones than that in the v-K-ras-expressing clones and the parental cells. Those domes flattened within 24 h after treatment with a specific inhibitor of Na(+)-K(+)-ATPase, ouabain, and the number of domes decreased in dose-dependent manner, indicating that Na(+)-K(+)-ATPase activity was required for maintainance of domes. These results suggest that up-regulated activity of H-ras but not of K-ras facilitates the vectorial fluid transport through a chorionic cell layer and leads to the dome formation. The function of II-ras in trophoblasts, may therefore, be essential for embryogenesis, especially for supplying the nutrients.

Expression of c-Ki-ras in developing rat liver

1. Two major c-Ki-ras transcripts are present in rat liver throughout development. 2. Both transcripts are functional, i.e. translatable into ras protein. 3. They exhibit low levels in early foetuses and increase gradually towards term. 4. Peak levels of transcripts are detected on the fourth day of postnatal life. 5. Results from nuclear run-off assays demonstrate that the rise in level of transcripts is a result of increase in rate of transcription with the highest rate detected on the fourth day of postnatal life. 6. Western blot analysis reveals that the accumulation of c-Ki-ras protein clearly follows the pattern of changes in transcription of c-Ki-ras gene.

Effect of vitamin E succinate and a cAMP-stimulating agent on the expression of c-myc and N-myc and H-ras in murine neuroblastoma cells

D-Alpha-tocopheryl succinate (vitamin E succinate) at a concentration of 11.3 microM inhibited growth and reduced the expression of c-myc, N-myc and H-ras specific mRNAs in murine neuroblastoma cells (NBP2) in culture. R020-1724 [4-(3-butoxy-4-methoxybenzyl)-2- imidazolidinone], an inhibitor of cyclic AMP phosphodiesterase, also inhibited growth and reduced the expression of these oncogenes. Vitamin E succinate treatment caused the formation of two c-myc related transcript of 1.9 and 3.7 kb; however, R020-1724 treatment did not. These results suggest that the inhibition of growth is sufficient to reduce the expression of c-myc, N-myc and H-ras in NB cells in culture, but it is not sufficient to produce two c-myc related transcripts.

Regulation of Ki-ras expression in Reuber H35 cells

Glucagon at a low concentration has a stimulatory effect on Ki-ras expression, whereas, at high concentrations the hormone suppresses the level of the Ki-ras transcripts. Incubation of the hepatoma cells with 10 microM dibutyryl cyclic AMP results in suppression of Ki-ras expression but the phorbol ester, 21-O-tetradecanoylphorbol 13-acetate (TPA) causes an increase. Down regulation of protein kinase C by prolonged exposure of hepatoma cells to TPA causes a dramatic decrease in the glucagon-stimulated effect on Ki-ras expression. The presence of diacylglycerol for 2 h in the culture medium results in a significant increase in Ki-ras expression, while treatment of the cells with 1-(5-isoquinolinylsulphonyl)-2-methylpiperazine, a potent inhibitor of protein kinase C, leads to a dramatic reduction. The calcium ionophore, A23187 is able to stimulate Ki-ras expression, whereas, addition of verapamil or EGTA results in its suppression. The present findings suggest that the inductive effect of glucagon on Ki-ras expression at low concentrations is via the activation of protein kinase C which causes phosphorylation of some regulatory proteins that may eventually affect the level of Ki-ras mRNA. The suppressive effect of glucagon at higher concentrations is via an increase in cAMP through activation of adenylate cyclase.

Isolation and characterization of Kirsten murine sarcoma virus-transformed mouse keratinocytes resistant to transforming growth factor beta

BALB/MK (MK) is a continuous murine keratinocyte line whose cells are strictly dependent on exogenous epidermal growth factor (EGF) for growth in culture. A derivative cell, KC, resulted from Kirsten murine sarcoma virus transformation, and these cells no longer require EGF for their growth. Despite differences in MK and KC growth conditions, both cell lines are growth inhibited by picomolar concentrations of transforming growth factor-beta (TGF-beta). When MK and KC cells were maintained in the presence of TGF-beta, resistant variants eventually proliferated only from the KC population. In an attempt to determine the mechanism of development of TGF-beta resistance, the TGF-beta-resistant cells (KCR cells) were compared with TGF-beta-sensitive KC cells with regard to growth properties, TGF-beta 1 binding characteristics, and gene expression. KCR cells continued to synthesize DNA and proliferated in the presence of TGF-beta 1 concentrations up to 2 nM, which was 500-fold greater than the ED50 for the sensitive cells. Although the KCR cells possess similar receptor numbers and affinity for TGF-beta 1, we observed differences in affinity cross-linking studies. The KCR cells expressed more of the type III, high molecular weight cell surface binding protein and less of the type II than the KC cells. The type I moiety was clearly altered to a smaller size in some, but not all, KCR cells. In gene regulation studies, there was no apparent difference in c-Ki-ras and v-Ki-ras mRNA levels in the KC and KCR cells. Additionally, expression of TGF-alpha and TGF-beta 1 mRNA was similar in MK, KC, and KCR cells. The expression of proliferation-associated genes, such as c-myc and MGSA/c-gro/kc, which were markedly decreased by TGF-beta 1 in the MK and KC cells, was not altered by TGF-beta 1 in the KCR cells. The data suggest that the loss of TGF-beta 1 responsiveness in the KCR cells was due to an alteration in the TGF-beta receptor that did not permit signal transduction, although the existence of postreceptor alterations cannot be excluded.

Spontaneous progression of hyperplastic outgrowths of the D1 lineage to mammary tumors: expression of mouse mammary tumor virus and cellular proto-oncogenes

Mammary cancer in mice is characterized by progression through defined stages of preneoplasia, with the most common preneoplastic stage being the hyperplastic alveolar nodule (HAN). We determined the relative levels of RNA expression of various cellular proto-oncogenes and endogenous mouse mammary tumor virus genes in outgrowths and tumors of three sublines of the transplantable D1 HAN preneoplastic outgrowth line. The three sublines differed in relative tumor-producing capabilities. Subline D1B produced a high incidence of tumors with short latency periods, whereas sublines D1C and D1D produced low incidences of tumors with long latency periods. No consistent alteration in proto-oncogene expression correlated with relative tumorigenicity, although tumors frequently contained higher levels of one or more proto-oncogene transcripts as compared with preneoplastic tissue. Slightly elevated (2- to 6-fold) levels of different oncogene transcripts were detected in 13 of 17 tumors as compared with outgrowth tissue, including abl (2 tumors), fps (5 tumors), Ha-ras (6 tumors), and Ki-ras (8 tumors). One tumor contained 45 times more Ki-ras-specific RNA than outgrowth tissue because of a comparable amplification of Ki-ras DNA sequences. Elevated levels of Ha-ras occurred more frequently in tumors of a high-incidence subline than in a less-aggressive subline (5/10 vs 1/7), but this difference was not statistically significant. However, consistent changes in MMTV expression accompanied progression from preneoplastic tissues to mammary tumors. All 17 tumors displayed reduced levels of the MMTV-specific long terminal repeat (LTR) transcript (1.6 kb) as compared with HAN tissue; tumors with moderate levels of LTR transcript expressed the 3.8-kb envelope message as well, one not detected in HANs. Expression of the LTR transcript is apparently influenced by factors in addition to the methylation status of endogenous mouse mammary tumor virus genes, which was similar in outgrowths and tumors. As the survey of representative proto-oncogenes failed to identify a uniform change between HAN and tumors, it is likely that other genes are involved in tumor progression in the mammary gland.

Oncogene expression in vivo by ovarian adenocarcinomas and mixed-mullerian tumors

Six-micron paraffin sections of paraformaldehyde-fixed specimens of 24 ovarian benign and neoplastic specimens were assayed for tumor cell-specific oncogene expression by a sensitive, quantitative in situ hybridization technique with probes for 17 oncogenes, beta-actin, and E. coli beta-lactamase. In the benign, borderline, and invasive adenocarcinomas, multiple oncogenes, including neu, fes, fms, Ha-ras, trk, c-myc, fos, and PDGF-A chains, were expressed at significant levels relative to a housekeeping gene (beta-actin). In the mixed-Mullerian tumors, a rather different pattern of oncogene expression was observed, characterized primarily by expression of sis (PDGF-B chain). For the adenocarcinomas, statistical analysis demonstrated that expression of several genes (fms, neu, PDGF-A) was closely linked to others (c-fos, c-myc) known to have important roles in the control of cell proliferation, but only one gene, fms, correlated very strongly with clinicopathologic features (high FIGO histologic grade and high FIGO clinical stage) predictive of aggressive clinical behavior and poor outcome. The authors discuss the role that tumor epithelial cell expression of the fms gene product might play in the auto- and paracrine control of growth and dissemination of ovarian adenocarcinomas.

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.

The isolation of recombinant RNA species responsive to oestrogen and tamoxifen in rat uterus and MCF-7 cells

We have previously shown that oestrogen elicits profound effects on the mRNA population of the immature rat uterus. In order to follow these responses in a more precise manner, we have prepared a cDNA library to uterine mRNA and screened this for sequences most responsive to the hormone. The stimulatory effect of oestrogen and tamoxifen on the levels of selected uterine mRNA species has been compared with the effect of the hormone and its agonist on total uterine poly(A)+ RNA levels. Two of the selected recombinant species were also expressed in the MCF-7 breast carcinoma cell line where their relative levels were again stimulated by oestrogen. Tamoxifen greatly reduced the poly(A)+ RNA levels of MCF-7 cells.

Down regulation of c-myc, c-fos and erb-B during estrogen induced proliferation of the chick oviduct

Oncogenes c-myc, H-ras, c-fos and erb-B were constitutively expressed in immature chick oviduct withdrawn from estrogen administration for 2.5 weeks after 10 d of primary estrogen stimulation. Following secondary estrogen stimulation of the withdrawn chicks, synthesis of egg white proteins is rapidly induced and remaining non-functioning tubular gland cells are stimulated to proliferate with a doubling time of 24 h. During first 12 h of secondary estrogen stimulation, H-ras mRNA levels doubled and did not increase further at 24 h and 48 h. The steady state levels of c-myc, erb-B and c-fos mRNA decreased 24 h following secondary estrogen stimulation. The levels of these oncogene RNAs in oviduct were similar at 48 h following secondary estrogen stimulation to those from immature chicks administered 10 d of primary estrogen stimulation. Thus elevated expression of c-myc and c-fos mRNA does not appear to be necessary components for sustained estrogen induced cell proliferation in the chick oviduct.

Oncogene expression in differentiating F9 mouse embryonal carcinoma cells

Differentiation of F9 mouse embryonal carcinoma cells in culture is accompanied by a decrease in growth rate and loss of tumorigenicity. Cells differentiating in monolayer culture (to parietal endoderm-type cells) or in aggregates (to visceral endoderm-type cells) show qualitatively similar changes in transcript levels from several c-oncogenes. In contrast with other studies with F9 cells, we find an early decrease in c-myb RNA but not in c-myc RNA. This and a later increase in c-src RNA may be associated with decreasing cell growth rate. Before differentiation, induction and maintenance of elevated c-abl RNA levels depend on the presence of retinoic acid in the medium. After differentiation c-abl RNA levels decline only partially when retinoic acid is removed. Increased RNA from c-fos is seen late in differentiation in monolayer cultures only, a change also seen with appearance of similar endoderm cell types in the developing mouse embryo.

Activation of endogenous MMTV proviruses in murine mammary cancer induced by chemical carcinogen

A study was undertaken to determine whether activation of expression of silent endogenous mouse mammary tumor virus (MMTV) proviruses may occur during tumor induction by a chemical carcinogen. A series of transplantable mammary tumors induced in BALB/c mice by treatment with dimethylbenz(alpha)anthracene (DMBA), pituitary isograft, or both was examined. The results obtained suggest that chemical carcinogens may induce mammary tumors through more than one pathway. Two of 9 tumor lines produced virus-specific products at levels above those observed during the course of normal mammary gland development. One tumor contained high levels of MMTV-specific envelope [3.8 kilobase (kb)] and genomic length (8.9 kb) RNAs. This tumor expressed core- and envelope-related proteins detectable by immunoblotting (including p28, gp52, and gp36), displayed an acquired provirus with a restriction map different from those of described exogenous MMTV strains, and contained abundant virus particles. The other tumor that expressed high levels of MMTV gene products contained envelope-specific (3.8 kb) and long-terminal-repeat-specific (1.6 kb) messages but no full-length RNA. It exhibited an aberrant 39 kDa, envelope-related protein, but no virus particles. Methylation data implicated the usually silent endogenous Mtv-8 provirus as the source of the abnormal envelope protein. None of the tumors expressed RNA from the putative mammary oncogenes, int-1 or int-2. We propose that chemical carcinogens may activate different cellular genes by mutation and that, in a subset of DMBA-induced mammary tumors, the target genes include endogenous MMTV proviruses that are normally not expressed. The effect on provirus expression varies from tumor to tumor, but is stable over passage of a given tumor. MMTV may be of etiological importance in the genesis of those DMBA-induced tumors which contain high levels of MMTV-specific products, but its action in the BALB/c system is not mediated through enhanced expression of the int-1 or int-2 preferred integration regions.

Definition of a region required for transformation in E1a of adenovirus 12

In order to define functionally important regions of the E1 a gene of adenovirus 12 (Ad12), a number of Ad12 mutants were studied. These mutants share an identical 69-bp deletion in the first exon of E1a as well as duplications of a long terminal repeat sequence at the end of the Ad12 genome. The mutants are fully competent for replication and growth in their normal hosts and have a host range extended to include the Vero cell line of African green monkey origin. The partially deleted E1a can stimulate the expression of all early adenoviral genes as well as the cellular heat shock gene, the transcription of which is stimulated by Ad5 E1a. However, plasmids containing the deleted E1a plus wild type E1b were unable to effect a transformation of either primary rat embryo fibroblasts or on an established cell line following transfection. Further, the mutant viruses were defective in generating tumors in newborn hamsters. We conclude that the deleted sequence of E1a described here is critical for transformation by E1a but is not necessary for multiplication of the virus or the transcriptional activating function of the gene.

Enhanced expression of four cellular oncogenes in a human glioblastoma cell line

Examination of a human glioblastoma cell line displaying a relatively stable karyotype and absence of both copies of chromosome #13 (HeRo) as well as of a SV-40 transformed subline (HeRo-SV) using analysis on the DNA and RNA level showed that both cell lines express high levels of abl, erb B, myc, and Ha-ras mRNA. Neither gene amplification nor gene rearrangement at the loci concerned nor abnormal transcription account for this activation of expression. The possible influence of the deleted sequences in the context of a suppressor gene hypothesis is discussed.

Expression of protooncogenes in murine osteosarcomas

The expression of 7 protooncogenes (c-sis, c-abl, c-mos, c-bas, c-Ki-ras, c-fos, c-myc) was examined in transplants and established cell lines from spontaneous and radiation-induced murine osteosarcomas. The transplant tumors were compared with different tissues, particularly skeletal tissue (sternum), and the osteosarcoma cell lines with fibroblast lines from the same mouse strains. C-sis was expressed above the level of controls in 2 osteosarcomas (TV, Os5). Three osteosarcomas showed over-expression of c-abl (TVK, DOS, Os5), c-bas (DOS, Os5 and V893) and c-fos (TVK, DOS, Os5), and 4 osteosarcomas showed over-expression of c-Ki-ras (TVK, DOS, Os5, Os16) and c-myc (TVK, DOS, TV, Os5). C-mos expression was not observed under the conditions used. One cell line (Os5) showed an altered transcript (1 kb transcript of c-fos). Apart from the relatively frequent increase in expression of the c-myc and c-ras-family, there was no indication that any particular protooncogene or combination of protooncogenes was associated with murine osteosarcomas.

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.

Studies on four cellular proto-oncogenes and their expression in PCC4 embryonal carcinoma cells: amplification of c-Ki-ras oncogene

We examined the expression of four cellular proto-oncogenes in two teratocarcinoma cell lines, one undifferentiated and malignant (PCC4), one differentiated and non malignant (PCD1). In this paper we report that transcript levels of c-Ki-ras, c-myc and c-fos are significantly higher in PCC4 cells whereas transcripts of c-Ha-ras are unchanged. Southern blot analysis does not reveal any structural alteration of c-myc and c-fos in PCC4 cells. On the contrary, the c-Ki-ras proto-oncogene is amplified 10 to 20 fold in PCC4 cells.

Assignment of three rat cellular RAS oncogenes to chromosomes 1, 4, and X

Mouse hepatoma-rat hepatocyte hybrids that segregate rat chromosomes were used to determine the chromosomal localization of rat cellular RAS genes. The cellular KRAS gene, homologous to the Kirsten sarcoma virus oncogene was mapped to rat chromosome 4, a chromosome that is often present in three copies in rat neurogenic tumor cells and transformed glial cells. The rat cellular HRAS-1 gene, homologous to the Harvey sarcoma virus oncogene was assigned to chromosome 1, whereas its intron-less counterpart HRAS-2 was mapped to the X chromosome. Since the human HRAS-2 also resides on the X chromosome, it appears that the cellular HRAS-2 gene (or pseudogene) conserved its chromosomal localization during mammalian evolution.

Expression of myb, myc and fos proto-oncogenes during the differentiation of a murine myeloid leukaemia

It is widely thought that c-onc genes (or proto-oncogenes)--the cellular progenitors of retroviral transforming genes--are involved in cellular differentiation and/or proliferation. Such ideas originate primarily from the ability of v-onc genes and 'activated' c-onc genes to induce uncontrolled cellular proliferation, and their capacity to arrest or interfere with differentiation processes in some systems. Haematopoietic cell populations provide additional support for these ideas as c-myb RNA is present in cell lines corresponding to immature, but not mature, cell types, and elevated levels have been found in tissues that are active in haematopoiesis. We have now examined the effects of induced differentiation on c-onc gene expression in a murine myeloid leukaemia cell line, WEHI-3B ('D+' subline). Our results show that the expression of c-myb and c-myc, at the level of transcription, decreases only at late stages in the monocytic differentiation of WEHI-3B cells, while expression of c-fos increases markedly. We suggest that c-myb and c-myc do not themselves control myeloid differentiation, but that they function in the maintenance of the proliferative state of myeloid cells. The induction of c-fos may reflect its role in some macrophage-specific functions.

Cell-cycle control of c-myc but not c-ras expression is lost following chemical transformation

Cellular oncogenes are DNA sequences implicated in the genesis of cancer, but their functions in the transformation process are not understood. Our experiments provide data linking expression of two well-studied proto-oncogenes, c-myc and c-rasKi, to current knowledge of proliferation control and its perturbation by differentiation and chemical transformation. Growth stimulation of quiescent cells by serum elevates expression of the myc proto-oncogene in Balb/c 3T3 (A31) cells. In two chemically transformed A31 derivatives (BPA31 and DA31), c-myc expression is constitutive. The levels of c-myc mRNA in quiescent and growing transformed cells are nearly the same, and are only slightly elevated compared to the level found in growing A31 cells. By contrast, c-rasKi expression is cell-cycle-dependent in BPA31 cells. The relative abundance of c-rasKi mRNA begins to increase in mid- to late G0/G1. During terminal differentiation of teratocarcinoma stem cells (F9) into nonproliferating endoderm, relative mRNA abundance is diminished more markedly for c-myc than for c-rasKi. These results demonstrate that expression of the myc and rasKi proto-oncogenes is dependent upon the cellular growth state, and that growth control exhibits growth-factor-dependent, cell-cycle-timed oncogene expression. In the case of the BPA31 cells, c-myc is not rearranged, amplified, or overexpressed. However, the oncogene has lost its cycle-dependent regulation in the chemically transformed cells.

Activation of Ki-ras2 gene in human colon and lung carcinomas by two different point mutations

Kirsten (Ki)-ras cDNA clones were prepared from human lung and colon carcinoma cell lines expressing an activated c-Ki-ras2 gene. DNA sequence analysis and transfection studies indicate that different point mutations at the same codon can activate the gene; that most human c-Ki-ras2 mRNA uses sequences from a fourth coding exon distinct from that of its viral counterpart; and that at least one cell line is functionally homozygous for the activated gene.

Retroviral transforming genes in normal cells?

The hallmark of retroviral transforming genes (onc genes) are specific sequences which are unrelated to essential virion genes but are closely related to sequences in normal cells. Viral onc genes probably originated from rare transductions of these cellular sequences by retroviruses without onc genes. Consequently, it has been suggested that retroviral transforming genes are present in normal cells in a latent form. However, recent structural analyses indicate that viral onc genes and cellular genes, which share specific sequences, are not isogenic. They differ from each other in scattered point mutations and in unique coding regions. The cellular genes containing onc-related sequences are expressed in normal cells compatible with a normal function. There is as yet no functional or consistent circumstantial evidence that these cellular genes cause cancer in animals that are not infected by viruses with onc genes. Therefore, it is still uncertain whether the onc-related cellular genes have oncogenic potential beyond their role as progenitors of retroviral onc genes.

A cellular oncogene (c-Ki-ras) is amplified, overexpressed, and located within karyotypic abnormalities in mouse adrenocortical tumour cells

The cellular oncogene c-Ki-ras is amplified 30- to 60-fold in cells of the mouse adrenocortical tumour Y1. The amplified oncogene is located in double minute chromosomes and in a homogeneously staining chromosomal region, common karyotypical anomalies of tumour cells. The amounts of c-Ki-ras specific mRNA and of the protein (p21) encoded by the amplified gene are correspondingly elevated. Amplification and enhanced expression of cellular oncogenes may contribute to the genesis and/or maintenance of at least some naturally occurring tumours.

Identification of transforming gene in two human sarcoma cell lines as a new member of the ras gene family located on chromosome 1

A molecular clone containing part of the transforming gene from two human sarcoma cell lines, HT1080 and RD, has been obtained and shown to represent a new member of the human ras gene family. The transforming gene has undergone no major rearrangements and has not been amplified in either sarcoma cell line. The major transcript from the gene is 2,200 nucleotides long and is present at the same levels in both normal fibroblasts and tumour cells. The same gene is also activated in HL60, a promyelocytic leukaemia line and in SK-N-SH, a neuroblastoma line. The gene, N-ras, is located on chromosome 1.