Alterations In Proto-oncogenes Research Articles

Molecular and immunopathology studies of oncogenes and tumor-suppressor genes in bladder cancer.

Target genes implicated in cellular transformation and tumor progression have been divided into two categories: proto-oncogenes (that when activated become dominant events characterized by gain of function) and tumor-suppressor genes (recessive events characterized by the loss of function). Alterations in proto-oncogenes and tumor-suppressor genes seem equally prevalent among human cancers. Multiple mutations appear to be required to conform the malignant phenotype. It is therefore conceivable that cancer be viewed fundamentally as a genetic disease entailing inherited (also called germ-line) and/or acquired (also termed somatic) mutations of genes in these two categories. Molecular studies of bladder neoplasms have identified a series of nonrandom genetic alterations affecting a particular set of oncogenes and tumor-suppressor genes. Because the modality of therapy for patients with bladder neoplasms primarily depends on morphological evaluation and clinical staging, the diagnosis carries significant consequences. However, it is well known that morphologically similar tumors presenting in any assigned stage may behave in radically different fashions, which seriously hampers the physician's ability accurately to predict clinical behavior in a given case. Recent studies have shown that inactivation of certain tumor-suppressor genes, such as RB and TP53, occur in bladder tumors that have a more aggressive clinical outcome and poor prognosis. In the present paper we review the molecular abnormalities associated with these dominant and recessive genes in bladder cancer and discuss the potential clinical use of their detection. The implementation of objective predictive assays to identify these alterations in clinical material will enhance our ability to assess tumor biological activities and to design effective treatment regimens. The need now is to translate this newly developed scientific knowledge into diagnostic and therapeutic strategies, which in turn will enhance the quality of life and prolong the survival of patients with bladder cancer.

Deletion of cyclin-dependent kinase 4 inhibitor genes P15 and P16 in non-Hodgkin's lymphoma

B-cell non-Hodgkin's lymphoma (NHL) is a heterogeneous lymphoid malignancy consisting of several histologic types. Alterations in proto-oncogenes caused by reciprocal chromosome translocations have been implicated in the etiology of specific histologic groups. In this study, we examined the contribution of the cell cycle inhibitor genes P15, P16, and P18 to pathogenesis in a large panel of 209 cytogenetically characterized B-cell NHL tumors representing varied histologic groups. We identified the homozygous deletion of P15 and P16 genes in 13 tumors from 12 patients, all belonging to diffuse large-cell histology; 10 had this diagnosis made on presentation, 1 had transformed from small lymphocytic lymphoma, and 1 had transformed from Hodgkin's disease. Tumor-specific point mutations were not identified in the coding regions of these genes. Cytogenetically, chromosome 9p was normal in all but one tumor. On the other hand, eight tumors hemizygous for 9p by cytogenetic analysis showed wild-type configuration of these genes. Our study, therefore, indicates that deletion of P15 and P16 occurs in about 15% of diffuse large-cell NHL and is not usually detected by cytogenetic analysis. P18 was wild-type in all tumors including the 13 tumors hemizygous for 1p.

Deletion of Cyclin-Dependent Kinase 4 Inhibitor Genes P15 and P16 in Non-Hodgkin's Lymphoma

B-cell non-Hodgkin's lymphoma (NHL) is a heterogeneous lymphoid malignancy consisting of several histologic types. Alterations in proto-oncogenes caused by reciprocal chromosome translocations have been implicated in the etiology of specific histologic groups. In this study, we examined the contribution of the cell cycle inhibitor genes P15, P16, and P18 to pathogenesis in a large panel of 209 cytogenetically characterized B-cell NHL tumors representing varied histologic groups. We identified the homozygous deletion of P15 and P16 genes in 13 tumors from 12 patients, all belonging to diffuse large-cell histology; 10 had this diagnosis made on presentation, 1 had transformed from small lymphocytic lymphoma, and 1 had transformed from Hodgkin's disease. Tumor-specific point mutations were not identified in the coding regions of these genes. Cytogenetically, chromosome 9p was normal in all but one tumor. On the other hand, eight tumors hemizygous for 9p by cytogenetic analysis showed wild-type configuration of these genes. Our study, therefore, indicates that deletion of P15 and P16 occurs in about 15% of diffuse large-cell NHL and is not usually detected by cytogenetic analysis. P18 was wild-type in all tumors including the 13 tumors hemizygous for 1p.

CUMULATIVE GENE AND CHROMOSOME ALTERATIONS ASSOCIATED WITH IN-VITRO NEOPLASTIC TRANSFORMATION OF HUMAN CERVICAL CELLS

The development of cancer is a multistep process requiring cumulative genetic alterations. An in vit ro model utilizing human cervical cells and papillomaviruses (HPV) that mimics human cervical cancer has been developed. Chromosome and gene alterations associated with distinctive stages of neoplastic transformation were demonstrated with an exocervical cell line obtained after sequential transfection with recombinant HPV-16 DNA and v-Ha-ras oncogene. Acquisition of immortality after HPV-16 transfection was associated with aneuploidy, structural changes of chromosomes 8, 10, 17, 19, 20, and 21, as well as proto-oncogene alterations. HPV-16 DNA was localized to two sites on chromosome 21, with one site at 21q22.2-22.3 near the ets-2 proto-oncogene. Ets-2 as well as c-myc gene mRNA levels were elevated in HPV immortal cells compared to primary nontransfected exocervical strains. Although the HPV-immortalized cells had several features characteristic of malignant cells, they lacked tumorigenic potential. Tumorigenicity occurred after transfection with v-Ha-ras oncogene, which was found stably integrated on chromosome 12 at the telomeric band q24.3. The tumorigenic line had additional clonal chromosomal abnormalities; consisting of multiple deletions involving regions of chromosomes 1p/q, 3p, 9q, loss of one copy of chromosome 11, and a complex rearrangement of chromosomes 8 and 13 as shown by in situ suppression hybridization with whole chromosome probes. Loss of tumor suppressor genes on deleted regions may have contributed to the acquisition of tumorigenicity. The genetic changes observed in these cells parallel those found in cervical carcinomas, demonstrating the validity of the in vitro model for studying the multistep progression resulting in cervical carcinoma.

Gene amplifications in advanced-stage human prostate cancer

Gene amplification is a model of proto-oncogene alterations occasionally observed in human tumors. This amplification can, in some cases, have prognostic value (N-myc in neuroblastoma, c-erbB2 and int-2 in breast cancer, etc.). Amplifications of the proto-oncogenes c-myc, c-erbB2 and int-2 have not yet been report in prostate adenocarcinoma, which, like breast cancer, is hormone dependent. We sought amplifications of these three proto-oncogenes by means of Southern blotting in 15 human prostate adenocarcinoma specimens, most of which were advanced (7 stage C and 6 stage D1 or D2). We confirmed the lack of c-myc and c-erbB2 amplification, regardless of the stage, in contrast to the case of breast cancer. Int-2 amplification was observed in one advanced tumor with bone metastases, out of a total of six stage D tumors. The precise frequency of int-2 amplification and its role in prostate carcinogenesis remain to be determined.

Growth Factor Expression in Normal Peritoneum of Patients with Gynecologic Carcinoma

Both epidermal growth factor receptor (EGFR) and HER-2/neu (neu) have been found to be of prognostic importance in epithelial ovarian and endometrial carcinoma, but alterations in proto-oncogene expression of normal tissues of patients with gynecologic malignancies are unknown. Patients (118) undergoing laparotomy for gynecologic indications (78 ovarian cancer, 11 endometrial cancer, 19 benign gynecologic disease, 10 other cancers) had biopsies of normal peritoneum for quantitative assessment of neu and EGFR concentrations. Patients undergoing exploration for gynecologic malignancy were found to have significantly higher median neu expression in the peritoneal biopsies than patients with benign gynecologic disease (P = 0.002). Most patients in this study were found to have ovarian cancer, and median peritoneal neu expression was found to be significantly higher in patients with ovarian cancer versus benign ovarian masses (P = 0.0008) or any benign gynecologic disease (P = 0.004). No significant alteration of unbound EGFR was found in peritoneal biopsies of any of the groups of patients. No associations were found for a history of breast cancer, presence of ascites, or menopausal status with alteration of neu or EGFR expression in normal peritoneum. These findings of altered expression of neu in normal tissues of patients with ovarian cancer are suggestive of the presence of proto-oncogene alterations in loco-regional tissues of the peritoneum, such as might be seen if a paracrine influence existed between tumor and peritoneal cells. Alternatively, the alterations may represent subtle alterations of proto-oncogene expression of germ-line tissues.

Analysis of c-fos, c-jun, c-erbB1, c-erbB2 and c-myc in primary lung carcinomas and their lymph node metastases.

The purpose of this study was to identify possible alterations in proto-oncogenes (c-fos, c-jun, c-erbB1, c-erbB2 and c-myc) at the protein level in primary lung carcinomas and simultaneous metastatic lymph nodes of 21 patients. The analysis showed that proteins of c-jun and c-myc were expressed in a significantly higher frequency in metastases than in primary lung tumors. Gross differences were not found between primary tumors and metastatic tumors with regard to the expression of c-erbB1, c-erbB2 and c-fos. The finding of cases with a higher expression of c-jun and c-myc in lymph nodes suggests that metastatic capability may be higher in certain cell populations.

Growth factor independence and growth regulatory pathways in human melanoma development

This review concentrates on growth autonomy of tumor cells in relation to tumor progression. Human malignant melanoma serves as an example for progressive growth factor independence at subsequent stages of tumor progression. Mechanisms by which malignant cells acquire growth factor independence are discussed. In melanoma, deregulation of growth regulatory pathways has been described on four levels: 1) aberrant production of autocrine growth factors that substitute for exogenous growth factors (basic fibroblast growth factor [bFGF]); 2) alterations in the response to negative autocrine growth factors (interleukin [IL]-6 and transforming growth factor [TGF]-beta); 3) overexpression of epidermal growth factor receptors (EGF-R); and 4) alterations of cellular protooncogenes involved in signal transduction (RAS, MYB) and growth suppression (p53). In addition to bFGF and IL-6, multiple other growth factor genes are activated in malignant melanoma cells but not normal melanocytes. These include both chains of platelet-derived growth factor (PDGF), TGF-alpha, IL-1, IL-8, and tumor necrosis factor (TNF)-alpha. Of these, PDGF-B has been investigated in more detail. Melanoma-derived PDGF clearly does not act in a direct autocrine mode, but has important paracrine effects on normal tissue constituents, notably fibroblasts and endothelial cells, that are essential for tumor development in vivo. It is speculated that other melanoma-derived growth factors with as yet undefined functions similarly exert such paracrine or 'indirect' autocrine effects that cannot be sufficiently addressed in studies on cultured cells.

Cell growth regulation in epithelial ovarian cancer.

As in the case of other epithelial neoplasms, most ovarian cancers arise from single clones of cells that have undergone multiple genetic alterations. A comparison of normal and malignant ovarian epithelium has identified several differences in growth regulation by peptide growth factors, protooncogenes, and tumor suppressor genes. Recent articles and abstracts have been reviewed. The malignant ovarian epithelial phenotype has been associated with (1) autocrine growth stimulation by transforming growth factor-alpha, (2) loss of autocrine growth inhibition by transforming growth factor-beta, (3) mutation or amplification of ras in 2-12% of cases, (4) amplification of myc in 23% of specimens, (5) expression of fms in 56% of cases with potential autocrine stimulation by macrophage colony stimulating factor, (6) paracrine stimulation by macrophage products including interleukin-1, interleukin-6 and tumor necrosis factor, (7) overexpression of c-erbB-2 (HER-2/neu) in 30% of cases, and (8) mutation with consequent overexpression of p53 in 50% of advanced ovarian cancers. A poor clinical prognosis is associated with expression or overexpression of the epidermal growth factor receptor, fms, and HER-2/neu. Antibodies against the extracellular domain of the HER-2/neu gene product p185 inhibit the growth of tumor cells that overexpress HER-2/neu and are associated with marked decreases in diacylglycerol levels. The intracellular kinase domain is required for growth inhibition. Antibodies that inhibit growth stimulate phosphorylation of intracellular substrates. Ricin A chain monoclonal antibody conjugates that react with p185 also inhibit the growth of tumor cells that overexpress p185. The intracellular kinase region is not required for immunotoxin-mediated killing. Coexpression of HER-2/neu and the epidermal growth factor receptor has been observed in 65% of epithelial ovarian cancers and in a limited number of normal tissue from a fraction of donors. Multiple alterations in growth factors, protooncogenes and growth factors have been detected in different epithelial ovarian cancers. Inappropriate signalling from receptor tyrosine kinases may be particularly important for ovarian oncogenesis. Drugs that affect tyrosine kinase and phosphatase activity deserve attention as potential therapeutic agents for ovarian cancer. The extracellular domains of the HER-2/neu gene product p185 and the epidermal growth factor receptor may provide useful targets for serotherapy.

C-erbB-2 DNA Amplification and mRNA Expression in Human Primary Breast Tumors and Its Relationship to Other Prognostic Factors

In order to evaluate the involvement of cerbB-2 oncogene in the etiology and progression of breast cancer, DNA samples from 157 primary human mammary carcinomas were subjected to Southern and dot blot analyses for the presence of c-erbB-2 protooncogene alterations. None of 157 carcinomas analyzed showed c-erbB-2 rearrangement. Amplification of the c-erbB-2 was found in 28.6% (45/157) of the samples. Gene expression could be analyzed in only 97 of these tumors. High levels of c-erbB-2 transcripts were detected in 25.7% (25/97) of the tumor RNA preparations. Although there was a good correlation between c-erbB-2 overexpression and gene amplification, a significant proportion of the tumors showed overexpression in the absence of gene amplification or gene amplification without overexpression. A significant correlation between c-erbB-2 proto-oncogene alterations with the number of positive lymph nodes and tumor necrosis was found, suggesting that c-erbB-2 genetic alterations have a biological importance in the etiology of breast cancer.

Positive and negative growth control in multistage skin carcinogenesis.

Early studies on the multistep nature of tumour formation in mouse skin were instrumental in the evolution of the present concepts of tumour initiation, promotion and progression. More recently, the application of molecular genetics to the mouse skin model has led to the identification of a number of mutational alterations in both proto-oncogenes and tumour suppressor genes which are associated with specific stages of carcinogenesis in this particular system. This article aims to review our current understanding of the genetic and biological changes implicated in mouse skin carcinogenesis.KeywordsSpindle CellMouse SkinSkin CarcinogenesisSpindle Cell CarcinomaSimple Sequence Length PolymorphismThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Analysis of oncogene alterations in human endometrial carcinoma: Prevalence of ras mutations

The molecular genetics of human endometrial carcinoma have yet to be defined to any significant extent. Cell lines from 11 endometrial carcinomas were examined for alterations in proto-oncogenes that might predictably be present, based on existing data from the better-characterized human carcinomas of the uterine cervix, ovary, and breast. Codons 12, 13, and 61 of the Ha-ras, Ki-ras, and N-ras genes were examined for possible point mutations, and the c-erbB2/neu, c-myc, and epidermal growth factor receptor (EGFR) genes were examined for amplification or overexpression. Ras mutations were found in seven of 11 (64%) tumors, including three in codon 61 of Ha-ras (CAG----CAT) and four in codon 12 of Ki-ras (GGT----GAT in two and GGT----GTT in two). No evidence was found for amplification or overexpression of the c-erbB2 or EGFR genes in any tumor. One tumor contained amplified c-myc sequences and exhibited relative overexpression of c-myc. These data suggest that the amplification or overexpression of several proto-oncogenes frequently observed in other human gynecologic and breast tumors are not prevalent in endometrial carcinoma and that ras gene mutations are relatively common in this tumor type.

DNA alterations at proto-oncogene loci and their clinical significance in operable non-small cell lung cancer

DNA from tumor samples of 54 patients with operable non-small cell lung cancer (NSCLC) was analyzed to determine whether proto-oncogene alterations could be correlated with the clinical behavior of lung cancer. Among seven proto-oncogenes tested, changes in the copy number of Ha-ras, c-myc and c-raf-1 were found in only seven tumors. Most of them were epidermoid carcinomas without lymph node involvement (N0). In spite of a localized disease with complete surgical resection, six of these patients relapsed within a mean disease-free interval (DFI) of only 6.5 months. There is a significant correlation between DNA alterations at proto-oncogene loci and clinical relapse within 12 months of surgical resection (P less than 0.025).

The molecular genetics of human lung cancer

With the development of molecular biological techniques the search for genetic alterations in cancer cells has resulted in the beginning of a molecular description of cellular transformation. Most of these genetic changes occur in genes which have a role in the control of cellular growth and development, the proto oncogenes. In the last decade, it has become clear that the myc and ras oncogene families are important in the carcinogenesis of human lung cancers. The myc oncogenes are usually found to be altered in small cell lung cancer (SCLC), and these alterations appear to correlate with rapid growth and progression. Mutations in the Kras gene are specific for adenocarcinoma, a subclass of non small cell lung cancer (NSCLC). Kras gene mutations are closely associated with tobacco smoking, since all were found in adenocarcinomas from patients with a history of smoking. The erbB oncogene, which encodes the epidermal growth factor receptor, is often highly expressed in epidermoid carcinomas. The roles for other oncogenes, such as raf or myb, as well as those of "suppressor" genes remain to be investigated, but may be of paramount importance. The study of alterations in proto oncogenes may aid in the (sub)classification and diagnosis of lung cancer, and may yield useful prognostic information in the near future.

Oncogenes in hematologic neoplasia.

Proto-oncogenes are normal genes involved in cellular proliferation and differentiation. Structural alterations in these genes can convert them to oncogenes involved in the initiation or progression of malignancy. About 50 proto-oncogenes have been described and four different activation mechanisms are known. Proto-oncogene alterations specific for human hematologic malignancies are well characterized.

A unique pattern of proto-oncogene abnormalities in ovarian adenocarcinomas.

Twelve cases of ovarian adenocarcinoma were studied for alterations in proto-oncogenes, and a unique pattern of altered ras proto-oncogenes was observed. Amplification of ras-Ki was found in three of seven ovarian tumors and amplification of ras-Ha in one of 12. In contrast, ras-Ha amplification was not found in any of the 334 other tumors and ras-Ki amplification was only seen in breast cancer at a frequency of 3%. Other proto-oncogenes altered in ovarian adenocarcinomas included c-myc and c-erbb-2. Proto-oncogene abnormalities were more frequent in aggressive tumors of high histologic grade.

Novel combination of c-myc, N-myc and N-ras oncogene alteration in brain tumors

We have examined forty human brain tumors (neoplasias presenting an important incidence in Mexico), for cellular myc (c-myc), N-myc and N-ras proto-oncogene alterations. An elevated amplification and/or rearrangement of the oncogenes was detected in most samples (60% presenting alteration for c-myc, 54% for N-myc, 6% for N-ras and 60% for ras-related genes). The tumors were of different histological types and for some of them we detected either amplification and/or rearrangement of the oncogenes. We describe, for the first time, the alterations of two related genes (c-myc and N-myc) in the same tumor samples; in 64% of the analyzed samples, oncogene alterations were accompanied by enhanced expression of N-myc and ras-related genes. These results suggest an important role for c-myc, N-myc and N-ras oncogenes, in the development and progression of brain tumors.

Alterations of class I HLA genes in human colon cancers

Alterations of HLA class I genes were found in 3 of 12 human colon cancers. Rearrangements in HLA class I genes were observed in 2 cancers and amplification of HLA-coding genes was observed in 1 cancer. All 3 cancers were at an advanced stage. No examples of amplification or rearrangement in the HLA genes were found in 10 other tumours of diverse types. No alterations in the beta 2-microglobulin gene were observed in 22 human solid tumours included in this study. The association between alterations in HLA genes and proto-oncogenes in these tumours is discussed.

Abnormalities of protooncogenes in non-small cell lung cancer. Correlations with tumor type and clinical characteristics.

Twenty-seven primary non-small cell (NSC) lung cancers were analyzed for alterations of protooncogenes by DNA hybridization techniques. Abnormalities were found in 56% of tumors including ten of 16 adenocarcinomas, three of nine squamous cell cancers and two of two larger cell cancers. Five protooncogenes were found to be commonly altered in tumors at frequencies between 12% and 60%. These were c-myc, c-myb, c-ras-Ha, c-erbB-1 and c-erb-B-2. Alterations in c-erbB-1 and c-erbB-2 correlated with histologic type of tumor and were more common in advanced cancers. Allelic deletions of c-ras-Ha or c-myb were frequently observed in primary tumors which recurred or progressed after surgery (five of six). Analysis of protooncogenes may provide insights into the pathogenesis of lung cancer and may aid in predicting clinical behavior.

V-H-ras gene reduces IL-3 requirement in PB-3c mastocytes in vitro followed by autokrine tumor formation in vivo.

The search for the physiological functions of proto-oncogenes has led to the notion that some code for products involved in control of mitosis as growth factor or growth factor receptor. This association of proto-oncogenes with mitotic control elements is consistent with the hypothesis that changes of various proto-oncogenes correlate with the multistep process of human carcinogesis, and there are numerous reports on specific proto-oncogene alterations in various human malignancies. What is not known, however, is the nature of the involvement of an altered proto-oncogene with the malignant process, i.e., the precise pathogenic role of the protein.KeywordsAcute Myeloblastic LeukemiaMyelomonocytic LineCumulative Tumor IncidenceMitogenic CultureThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.