Tumor suppressor genes: the puzzle and the promise

Cytogenetic findings in 200 patients with multiple myeloma

Cytogenetic studies were performed in 200 consecutive patients with multiple myeloma and related disorders. Structurally or numerically abnormal clones were found in 63 patients (32%), including 8 of 45 untreated patients (18%), and 55 of 155 treated patients (35%). The abnormal karyotypes generally showed numerous numerical and structural aberrations and in some patients multiple abnormal clones. The most striking feature of patients with hyperdiploid karyotypes was the finding of consistent recurring trisomies for chromosomes 3, 5, 7, 9, 11, 15, 19, and 21, cosegregating together in many cases. Monosomy for chromosome 13 was the most common chromosome loss, occurring in 18 abnormal patients (29%), while interstitial deletions involving band 13q14 occurred in an additional 9 patients, indicating a loss of all or part of chromosome 13 in a high percentage of patients with abnormal karyotypes (43%). Structural aberrations of chromosome 1 were most frequent, occurring in 30 of 63 patients (48%), and involved almost equally the short and long arms. The single most frequent chromosome breakpoint involved band 14q32 and was found in 21 patients (33%), including 11 patients with a 14q+ chromosome, 8 with t(11;14)(q13;q32), and 2 with t(8;14)(q24;132).

Tumor suppressor genes and clonal evolution in B-CLL

This review highlights the genetic alterations that have been detailed in the malignant B-cell clones of patients with B-chronic lymphocytic leukemia (CLL). In particular, the alterations seen in p53 and the retinoblastoma (Rb) genes are reviewed. In addition, the multiplicity of cytogenetic alterations observed at baseline and on sequential analysis are summarized. The cytogenetic and molecular biologic analysis of B-CLL clones has revealed that there is a dynamic array of genetic events which occur within a B-cell clone. This latter data strongly suggests that clonal evolution may occur in B-CLL patients. However the relationship of the clonal instability to the patient's clinical course is still unclear. The relatively frequent detection of multiple tumor suppressor gene alterations in the B-CLL clones offer several interesting clues regarding the transformation event within B-CLL. A model is proposed which attempts to explain the potential contribution and interaction of p53 and Rb gene alterations in a malignant B-cell transformation.

Cytogenetics and molecular genetics of human solid tumours

It is generally accepted that cancer is a genetic disease resulting from the accumulation of multiple genomic rearrangements. These rearrangements involve gross chromosomal abnormalities (e.g. translocations and deletions) as well as submicroscopic mutations affecting both oncogenes and tumour suppressor genes. Recent studies of several tumour specific translocations in sarcomas have shown that the translocations result in so-called fusion genes. In this review we will discuss the specificity and implications of different genetic alterations in both sporadic and hereditary human solid tumours, and provide examples of how these changes can be used as tumour specific markers of both diagnostic and prognostic significance.

Isolation and characterization of a novel mitogenic regulatory gene, 322, which is transcriptionally suppressed in cells transformed by src and ras

In an attempt to isolate novel regulatory and/or tumor suppressor genes, we identified cDNAs whose abundance is low in NIH 3T3 cells and further decreased following the expression of the activated oncogene, v-src. The transcription of one such gene, 322, is suppressed at least 15-fold in src-, ras-, and fos-transformed cells and 3-fold in myc-transformed cells but is unaffected in raf-, mos-, or neu-transformed cells. Activation of a ts-v-src allele in confluent 3Y1 fibroblasts resulted in an initial increase in 322 mRNA levels after 1 to 2 h followed by a rapid decrease to suppressed levels after 4 to 8 h. Morphological transformation was not detected until 12 h later, indicating that the accumulation of 322 transcripts is regulated by v-src and not as a consequence of transformation. Addition of fetal calf serum to starved subconfluent NIH 3T3 or 3Y1 fibroblasts resulted in a similar biphasic regulation of 322, indicating that 322 transcription is responsive to mitogenic factors. Sequence analysis of a putative full-length 322 cDNA clone (5.4 kb) identified a large open reading frame (ORF) encoding a 148.1-kDa product. In vitro transcription and translation of the 322 cDNA from a T7 promoter resulted in a 207-kDa product whose electrophoretic mobility on a sodium dodecyl sulfate-polyacrylamide gel electrophoresis gel was unaffected by digestion with endoglycosidase F. The discrepancy in predicted versus measured molecular weights may result from the high percentage of acidic residues (roughly 20% Glu or Asp) in the 322 ORF product. Comparison of the 322 cDNA ORF with sequences in data banks indicates that this gene is novel. The 322 ORF product contains a potential Cys-1-His-3 Zn finger, at least five nuclear localization signals of the adenovirus E1a motif K(R/K)X(R/K), and alternating acidic and basic domains. Overexpression of the 322 cells resulted in the selection of rapidly growing cells which had lost the transduced 322 cDNA. Thus, 322 represent a novel src- and ras-regulated gene which encodes a potential regulator of mitogenesis and/or tumor suppressor.

The multiple tumor suppressor 1/cyclin-dependent kinase inhibitor 2 gene in human central nervous system primitive neuroectodermal tumor

The recently described multiple tumor suppressor 1/cyclin-dependent kinase inhibitor 2 (MTS1/CDKN2) gene, encoding the cyclin-dependent kinase 4 inhibitor p16, is mutated in a wide variety of tumor cell lines, including gliomas. To investigate the possible role of this gene in the genesis of the central nervous system primitive neuroectodermal tumor (PNET), four established PNET cell lines and 18 PNET surgical specimens were studied for deletions and mutations of the MTS1/CDKN2 gene. One of the four cell lines had homozygous deletion of the gene. No mutation in any of the three MTS1/CDKN2 exons was detected in the other three cell lines by single strand conformational polymorphism analysis. Eighteen surgical PNET specimens were studied for allelic and homozygous deletion at chromosome 9p21, the location of the MTS1/CDKN2 gene. No loss of heterozygosity was noted in 11 of the tumors, and no homozygous loss was noted in any tumor. Single strand conformational polymorphism analysis of the entire coding region of the MTS1/CDKN2 gene revealed no mutation within MTS1/CDKN2 in any tumor. Although deletion of MTS1/CDKN2 may occur in some PNET cell lines, neither deletion nor mutation of the gene is found in tumors before culture. The genesis of the human central nervous system PNET does not involve deletion or mutation of the MTS1/CDKN2 gene.

Understanding the biology of aging: the key to prevention and therapy

OBJECTIVE

To review recent progress and consider future approaches for basic research on aging with clinical applicability.

DATA SOURCES

Peer-reviewed publications on experimental gerontology and geriatrics.

STUDY SELECTION AND DATA EXTRACTION

Studies were selected that described experimental approaches in gerontology and geriatrics, starting with the evolutionary basis of aging, through theories trying to explain its major causes, to novel experimental approaches, e.g., computer informatics, protein chemistry and genetics.

DATA SYNTHESIS

Our increased understanding of the evolutionary basis of aging has made it possible to consider a number of experimental strategies more rationally. Most theories on the causes of aging involve some kind of somatic damage that accumulates with age, the rate of which is determined by environmental, genetic, and behavioral factors. The recent emergence of more powerful methodology offers new possibilities for identifying basic mechanisms of aging, which would increase our understanding of biologically based susceptibility to age-related health problems.

CONCLUSIONS

There is a growing awareness that age-related deterioration will affect an ever growing number of people, in both absolute and relative terms. It can be expected that this will further increase the resources that will be made available for research on aging. Although ultimately unavoidable, aging is a process that appears to be experimentally accessible. Therefore, the mechanisms of senescence and death may eventually be more completely understood, with the promise of preventing and/or delaying many of the adverse effects associated with aging, including most of the common diseases, and possibly also of extending lifespan.

Multiple neurofibromas of the spinal nerve roots

This report describes a rare case of a suspected neurofibromatosis type 1 patient who had multiple bilateral spinal neurofibromas from the cervical to the sacral spinal dorsal nerve roots. The lesions were readily detected by MR imaging and the largest tumour was successfully resected. We provide a brief review of the literature, emphasising the usefulness of MR imaging in the diagnosis and evaluation of spinal neurofibromas.

La citogenetica e la genetica molecolare nella prognosi del carcinoma della vescica: Cytogenetics and molecular genetics in bladder carcinoma prognosis

The use of cytogenetics in the characterization of bladder tumours has made it possible to demonstrate that chromosomal alterations are correlated with stage and grade of the tumour and have a predictive value as regards both tumour recurrences and progression. In the last decade the chromosomes involved in the main aberrations have been identified, and a negative prognostic significance has been suggested for some chromosomal aberrations. The knowledge of cytogenetics has been deepened by the sophisticated methods of molecular genetics, that have discovered many oncogenes and suppressor genes probably involved in the development of bladder tumours. The most characteristic molecular alterations of these tumours are losses of genetic information on chromosomes 9, 11 and 17, as a consequence of deletions and/or mutations. Such alterations probably cause the loss and/or the inactivation of suppressor genes (partly hypothetic still) and could represent important predictive factors of tumour progression.

Gene-modified cells for the treatment of cancer

Gene therapy involves the insertion of a gene into an organism to treat a disease. Since its early development in the 1970s, gene therapy has expanded rapidly both in terms of the methods available and the number of candidate diseases for treatment. This report reviews gene therapy for cancer, including methodology, pre-clinical studies and experimental clinical trials.

Prohibitin: potential role in senescence, development, and tumor suppression

Prohibitin is an evolutionarily conserved gene with homologues found in organisms ranging from yeast to man. In man the gene is located on chromosome 17 at q21. The deduced amino acid sequences of the protein products from mouse and rat are identical; and these differ from the human protein sequence by a single conserved amino acid. Prohibitin has antiproliferative activity and available data suggest a role in such diverse processes as normal cell cycle regulation, replicative senescence, cellular immortalization, and the development of sporadic breast tumors. Although its functional activity is presently unknown, the 30,000-Da protein has been located in the inner membrane of mitochondria, where it is postsynthetically modified, as well as on the plasma membrane of B cells, where it is associated with the IgM receptor. Prohibitin's evolutionary conservation and ubiquitous expression indicate that it is a fundamentally important gene; and current data suggest a functional role in such dissimilar processes as development, senescence, and tumor suppression.

The genetic basis of colorectal cancer--clinical implications

Colorectal carcinomas demonstrate extensive molecular genetic alterations throughout the genome. The genetic changes in cancer of the colon and rectum are among the best understood of any common human cancer. The genetic abnormalities include both dominant-acting oncogenes (Ki-ras, c-src) and tumor-suppressor genes which undergo inactivation or loss (APC, DCC, p53). The evolution of the cancer is a complicated and multistep process. At the various steps of this phenomenon we can recognize specific molecular genetic alterations. These particular genetic changes may be useful as improved markers to predict those patients who have an aggressive cancer of the colon, with occult metastases or increased metastatic capability and this selection of patients could lead to improved surgical and medical management.

Molecular characterization of the in vivo alkylating agent resistant murine EMT-6 mammary carcinoma tumors

The expression of several early-response genes and genes associated with malignant disease was assessed in the EMT-6/parent tumor and the EMT-6/CTX and EMT-6/CDDP in vivo resistant tumor lines growing as tumors or as monolayers in culture. In the absence of treatment the levels of mRNA for the genes c-jun, c-fos, c-myc, Ha-ras and p53 were increased in the EMT-6/CTX and EMT-6/CDDP as compared with the EMT-6/parent tumor, whereas the expression of erb-2 was similar in all three tumors. Although the cells from each of the three tumors show increased expression of early response genes after exposure to cisplatin (CDDP; 100 microM, 2 h) or 4-Hydroxyperoxycyclophosphamide (4-HC; 100 microM, 2 h) in culture, in mRNA extracted from tumor tissue these changes are absent or very small. Both C-jun and erb-2 were detectable in liver. There was increased expression of both of these genes in the livers of tumor-bearing animals as compared with non-tumor-bearing animals. The highest expression of both c-jun and erb-2 occurred in the livers of animals bearing the EMT-6/CDDP tumor. Treatment of the animals with CDDP or cyclophosphamide, in general, resulted in increased expression of both genes at 6 h post treatment. The increased expression of these genes may impart metabolic changes in the tumors and/or hosts that contribute to the resistance of these tumors to specific antitumor alkylating agents.

An overexpressed gene transcript in senescent and quiescent human fibroblasts encoding a novel protein in the epidermal growth factor-like repeat family stimulates DNA synthesis

We carried out subtractive enrichment of a cDNA library derived from mRNA of senescent human diploid fibroblasts (HDF) established from a subject with Werner syndrome of premature aging. By differential screening, we isolated an overexpressed cDNA sequence (S1-5) that codes for a novel protein containing epidermal growth factor (EGF)-like domains which match the EGF-like consensus sequences within several known extracellular proteins that play a role in cell growth, development, and cell signalling. S1-5 mRNA is overexpressed in Werner syndrome and senescent normal HDF, is induced by growth arrest of young normal cells, but is significantly decreased by high serum, conditions which promote cellular proliferation. Paradoxically, microinjection into young HDF of two different lengths of S1-5 mRNA, containing different putative AUG translational start sites, consistently stimulated rather than inhibited DNA synthesis by an apparent autocrine/paracrine mechanism. Thus, the S1-5 gene product may represent a negative and/or positive factor whose ultimate activity is modulated by the cell environment as occurs with other members of EGF-like family.

Nonrandomly-associated forward mutation and mitotic recombination yield yeast diploids homozygous for recessive mutations

We have employed the analysis of spontaneous forward mutations that confer the ability to utilize L-alpha-aminoadipate as a nitrogen source (alpha-Aa+) to discern the events that contribute to mitotic segregation of spontaneous recessive mutations by diploid cells. alpha-Aa- diploid cells yield alpha-Aa+ mutants at a rate of 7.8 +/- 3.6 x 10(-9). As in haploid strains, approximately 97% (30/31) of alpha-Aa+ mutants are spontaneous lys2-x recessive mutations. alpha-Aa+ mutants of diploid cells reflect mostly the fate of LYS2/lys2-x heterozygotes that arise by mutation within LYS2/LYS2 populations at a rate of 1.2 +/- 0.4 x 10(-6). Mitotic recombination occurs in nonrandom association with forward mutation of LYS2 at a rate of 1.3 +/- 0.6 x 10(-3). This mitotic recombination rate is tenfold higher than that of a control LYS2/lys2-1 diploid. Mitotic segregation within LYS2/lys2-x subpopulations yields primarily lys2-x/lys2-x diploids and a minority of lys2-x aneuploids. Fifteen percent of lys2-x/lys2-x diploids appear to have arisen by gene conversion of LYS2 to lys2-x; 85% of lys2-x/lys2-x diploids appear to have arisen by mitotic recombination in the CENII-LYS2 interval. lys2-1/lys2-1 mitotic segregants of a control LYS2/lys2-1 diploid consist similarity of 18% of lys2-1/lys2-1 diploids that appear to have arisen by gene conversion of LYS2 to lys2-1 and 82% of lys2-1/lys2-1 diploids that appear to have arisen by mitotic recombination in the CENII-LYS2 interval.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of p53, transforming growth factor alpha, epidermal growth factor receptor, and c-erbB-2 in endometrial carcinoma and correlation with survival and known predictors of survival

Abnormal expression of p53, transforming growth factor alpha (TGF alpha), epidermal growth factor receptor (EGFR), and c-erbB-2 occurs in a variety of cancers and in some cases is associated with poor prognosis. Immunoperoxidase staining using these markers in formalin-fixed, paraffin-embedded endometrial carcinoma tissue was performed to determine whether immunoreactivity correlates with survival and known prognostic variables. Cases included 84 endometrioid adenocarcinomas, five adenoacanthomas, 12 adenosquamous carcinomas, 11 serous carcinomas, 15 clear cell carcinomas, and one carcinosarcoma for a total of 128 cases. Frequencies of immunoreactivity were as follows: p53, 37 of 128 (29%); TGF alpha, strong (2+) 23 of 128 (18%) and intermediate (1+) 26 of 128 (20%); EGFR, strong (3+) 21 of 128 (16%) and intermediate (2+ or 1+) 83 of 128 (65%); and c-erbB-2, strong (2+) four of 128 (2%) and intermediate (1+) three of 128 (1%). p53 and TGF alpha staining showed statistically significant correlations with decreased length of survival (P < .0017 and P < .0013, respectively, generalized Savage [Mantel Cox]). p53 immunoreactivity correlated with tumor types, grade, and stage. Transforming growth factor alpha staining correlated with increased depth of invasion and presence of vascular invasion. Epidermal growth factor receptor staining did not correlate with length of survival or known prognostic variables. c-erbB-2 staining correlated with tumor type. In the multivariate analysis p53 and TGF alpha staining were not independent predictors of survival when other variables were taken into account, including grade, stage, tumor type, presence of vascular invasion, and depth of invasion. Grade and stage were the only independent predictors of survival when used in combination in a Cox proportional hazards model.

Isolation of two contigs of overlapping cosmids derived from human chromosomal band 3p21.1 and identification of 5 new 3p21.1 genes

Consistent loss of DNA sequences from several regions on the short arm of human chromosome 3 has suggested that multiple tumor suppressor genes reside on chromosome 3p in various types of cancer cells. We have focused our efforts on an analysis of chromosomal band 3p21.1 since aminoacylase-1 (ACY1), which is localized to this band, has been shown to have lower levels of expression in several small cell and non-small cell lung cancer cell lines. Starting with two cosmids within 3p21.1, D3S92 and D3S93, we have isolated two separate contigs of overlapping cosmids within 3p21.1, by screening a library of 5700 chromosome 3-specific cosmid clones. Detailed restriction maps for these two contigs show that they contain multiple clusters of rare cutting restriction endonuclease sites. One contig extends for 100 kb and encompassed both ACY1 and D3S92, and the other extends about 80 kb around the D3S93 locus. Many different restriction fragments derived from these two contigs were found to be evolutionarily conserved and hybridized to distinct message transcripts. These fragments were used to identify homologous cDNAs from an adenogastric cDNA library, and several of these cDNAs were partially sequenced. We have identified five new genes from these two contigs and there is evidence to suggest that several additional genes reside within these cosmid contigs. The genes identified from 3p21.1 were then hybridized to DNA, isolated from a series of lung cancer cell lines and matched normal and tumor DNA from lung cancer patients. No alterations were detected with any of these probes, both at the DNA or RNA levels. A similar analysis with DNA fragments derived from these two genomic regions also failed to detect any alterations.

Differentiation as symbiosis

Preservation of the identity of DNA is the ultimate goal of multicellular organisms. An abnormal DNA sequence in cells within an individual means its parasitic nature in cell society as shown in tumors. Somatic gene arrangement and gene mutation in development may be considered as de novo formation of parasites. It is likely that the developmental process with genetic alterations means symbiosis between altered cells and germ line cells preserving genetic information without alterations, when somatic alteration of DNA sequence is a major mechanism of differentiation. According to the selfish gene theory of Dawkins, germ line cells permit symbiosis when somatic cell society derives clear profit for the replication of original DNA copies.

The lack of v-src involvement in tumorigenicity of marmoset cells transformed in vitro with Rous sarcoma virus

The transformation of nonhuman primate marmoset cells by Rous sarcoma virus of Schmidt-Ruppin strain (RSV-SR) generates transformants which lack tumorigenicity in allo- and xenogeneic hosts. Marmoset cells acquire this property when they are transformed by RSV rescued from non-tumorigenic allogeneic cells. One of the rescued RSV, when used to infect marmoset kidney cells in vitro, yielded transformants which became tumorigenic in adult allogeneic hosts. Cytogenetic and molecular analyses of transformants revealed progressive genetic changes from cell diploidy to aneuploidy and from the presence to the loss of v-src during propagation in vitro. The loss of v-src in transformed cells coincided with the evolution of aneuploid cell clone with specific marker chromosome (M1). Although both early passage diploid and late passage aneuploid transformants were tumorigenic, the induced tumors originated from different type of cells. Tumors induced by diploid- and v-src-positive transformants were derived predominantly from the host cells, while tumors induced by late-passage transformants and with deleted v-src originated from an aneuploid cell clone that contained a rearranged M1 marker chromosome. These results suggest that besides the v-src oncogene, proviral integration can facilitate chromosomal rearrangements that contribute to tumorigenic transformation of nonhuman primate cells in vitro.

Etiopathology of feline toxic nodular goiter

We have discussed the etiopathology of feline toxic nodular goiter in the context of human nodular goiter pathogenesis. We have reviewed thyroid heterogeneity, growth regulation, functional and growth autonomy, nodule and tumor formation, and the evolution of toxic nodular goiter in the human being. By addressing toxic nodular goiter of the cat, the history, morphologic findings, xenotransplantation and cell culture studies, evidence for and against circulating thyroid stimulators and epizootiological studies of the feline disease have been summarized. Due to its structure, the thyroid gland offers some unique possibilities to study the mechanisms that are responsible for cellular heterogeneity, the emergence of autonomous nodular growth and function, and, ultimately, the development of tumors. The demonstration of naturally occurring clones of cells with high intrinsic proliferation potential within the follicular epithelium of the thyroid has fostered promising new concepts on the genesis of nodular growth of benign and possibly malignant endocrine tumors. Hyperthyroid cat goiters contain single or multiple, autonomously (i.e., TSH-independently) functioning and growing nodules. Neither hyperfunction nor growth of these nodules depends on extrathyroidal circulating stimulators. The basic lesion appears to be an excessive intrinsic growth capacity of some thyroid cells. The factors enhancing the transformation of a normal thyroid into a nodular hyperfunctioning goiter over many years are still unknown. Immunological, environmental, and nutritional factors are the focus of ongoing studies, but an infectious agent can not yet be excluded.

Chromosomal markers of immortalization in human breast epithelium

We describe a series of five immortal breast cell lines that have emerged independently from diploid cultures from two individuals. We have karyotyped representative cultures of each of these lines prior to and at intervals after immortalization. Although considerable diversity of chromosomal aberration was found among the five lines, analysis of sublines has defined the chromosomal changes common for each immortalization. These changes differed both within and between the individual patient sources. Some common alterations were noted in lines from both patients, however, including loss of the short arm of chromosome 20 and gain of 1q. We suggest that genes within these chromosomal regions contribute to spontaneous immortalization of human breast epithelium.

Loss of p53 protein during radiation transformation of primary human mammary epithelial cells

The causative factors leading to breast cancer are largely unknown. Increased incidence of breast cancer following diagnostic or therapeutic radiation suggests that radiation may contribute to mammary oncogenesis. This report describes the in vitro neoplastic transformation of a normal human mammary epithelial cell strain, 76N, by fractionated gamma-irradiation at a clinically used dose (30 Gy). The transformed cells (76R-30) were immortal, had reduced growth factor requirements, and produced tumors in nude mice. Remarkably, the 76R-30 cells completely lacked the p53 tumor suppressor protein. Loss of p53 was due to deletion of the gene on one allele and a 26-bp deletion within the third intron on the second allele which resulted in abnormal splicing out of either the third or fourth exon from the mRNA. PCR with a mutation-specific primer showed that intron 3 mutation was present in irradiated cells before selection for immortal phenotype. 76R-30 cells did not exhibit G1 arrest in response to radiation, indicating a loss of p53-mediated function. Expression of the wild-type p53 gene in 76R-30 cells led to their growth inhibition. Thus, loss of p53 protein appears to have contributed to neoplastic transformation of these cells. This unique model should facilitate analyses of molecular mechanisms of radiation-induced breast cancer and allow identification of p53-regulated cellular genes in breast cells.

Genetic aberrations in human brain tumors

Over the last decade, much has been learned about the genetic changes that occur in human neoplasia and how they contribute to the neoplastic state. Oncogenes and tumor suppressor genes have been identified, and many powerful molecular genetic techniques have emerged. Brain tumors have been intensively studied as part of this process. Specific and recurring genetic alterations have been identified and are associated with specific tumor types. In astrocytomas, for example, losses of genetic material on chromosomes 10 and 17 and amplification of the epidermal growth factor receptor gene seem important in pathogenesis, with the loss of chromosome 10 and the amplification of epidermal growth factor receptor being strongly associated with glioblastoma multiforme. Meningiomas, on the other hand, have usually lost part or all of chromosome 22. Brain tumors also express growth factors and growth factor receptors that may be important in promoting tumor growth and angiogenesis. These include epidermal growth factor, transforming growth factor-alpha, platelet-derived growth factor, the fibroblast growth factors, and vascular endothelial growth factor. In this article, we review the genetic aberrations that occur in the major types of brain tumors, including glial tumors, meningiomas, acoustic neuromas, medulloblastomas, primitive neuroectodermal tumors, and pituitary tumors. Wherever possible, clinical correlations have been made concerning the prognostic and therapeutic implications of specific aberrations. We also provide some background about the cytogenetic and molecular genetic techniques that have contributed to the description and understanding of these alterations and speculate as to some clinical and basic science issues that might be explored in the future.

Loss of p53 protein during radiation transformation of primary human mammary epithelial cells

The causative factors leading to breast cancer are largely unknown. Increased incidence of breast cancer following diagnostic or therapeutic radiation suggests that radiation may contribute to mammary oncogenesis. This report describes the in vitro neoplastic transformation of a normal human mammary epithelial cell strain, 76N, by fractionated gamma-irradiation at a clinically used dose (30 Gy). The transformed cells (76R-30) were immortal, had reduced growth factor requirements, and produced tumors in nude mice. Remarkably, the 76R-30 cells completely lacked the p53 tumor suppressor protein. Loss of p53 was due to deletion of the gene on one allele and a 26-bp deletion within the third intron on the second allele which resulted in abnormal splicing out of either the third or fourth exon from the mRNA. PCR with a mutation-specific primer showed that intron 3 mutation was present in irradiated cells before selection for immortal phenotype. 76R-30 cells did not exhibit G1 arrest in response to radiation, indicating a loss of p53-mediated function. Expression of the wild-type p53 gene in 76R-30 cells led to their growth inhibition. Thus, loss of p53 protein appears to have contributed to neoplastic transformation of these cells. This unique model should facilitate analyses of molecular mechanisms of radiation-induced breast cancer and allow identification of p53-regulated cellular genes in breast cells.

Negative regulators of cell proliferation

Cell proliferation is governed by the influence of both mitogens and inhibitors. Although cell contact has long been thought to play a fundamental role in cell cycling regulation, and negative regulators have long been suspected to exist, their isolation and purification has been complicated by a variety of technical difficulties. Nevertheless, over recent years an ever-expanding list of putative negative regulators have emerged. In many cases, their biological inhibitory activities are consistent with density-dependent growth inhibition. Most likely their interactions with mitogenic agents, at an intracellular level, are responsible for either mitotic arrest or continued cell cycling. A review of naturally occurring cell growth inhibitors is presented with an emphasis on those factors shown to be residents of the cell surface membrane. Particular attention is focused on a cell surface sialoglycopeptide, isolated from intact bovine cerebral cortex cells, which has been shown to inhibit the proliferation of an unusually wide range of target cells. The glycopeptide arrest cells obtained from diverse species, both fibroblasts and epithelial cells, and a broad variety of transformed cells. Signal transduction events and a limited spectrum of cells that are refractory to the sialoglycopeptide have provided insight into the molecular events mediated by this cell surface inhibitor.

Observations on tumor and metastatic suppressor gene status in endometrial carcinoma with particular emphasis on p53

BACKGROUND

Genetic changes in the development of endometrial carcinoma have not been characterized, and little is known of tumor or metastatic suppressor gene status in these malignancies. The current study on endometrioid carcinoma was undertaken to examine the status of two tumor suppressor genes that frequently have been found to be altered in human malignancies (the p53 gene and the retinoblastoma [Rb] gene) and to examine the status of the candidate metastatic suppressor gene, nm23-H1.

METHODS

The status of the p53 gene was studied by immunohistochemistry of formalin-fixed paraffin-embedded biopsy samples from 72 patients with atypical endometrial hyperplasia or endometrioid carcinoma who underwent hysterectomy immediately after biopsy and from 5 patients with benign endometria. A search for loss of heterozygosity (LOH) of the nm23 gene after DNA extraction from frozen tissues and hybridization with nm23-H1 cDNA specific probe was made in 10 endometrial carcinomas. Rb gene status was evaluated by image analysis quantification of immunoreactive retinoblastoma protein in frozen sections of 10 carcinomas and 2 benign endometria.

RESULTS

p53 expression was low in all benign endometria, but high expression was found in 2 (15%) of 13 atypical hyperplasias and in 23 (39%) of 59 carcinomas. High levels of p53 expression in endometrioid carcinoma correlated with the spread of disease outside of the uterus and by logistic regression, the presence of squamous differentiation, nuclear grade, and high p53 expression in the biopsy all independently correlated with spread of disease outside of the uterus. Although 7 of the 10 carcinomas studied were informative, LOH for the nm23 gene was not seen in any, including a site of metastasis. Rb protein expression in endometrial carcinoma was similar to expression in benign endometria.

CONCLUSIONS

Although this study found no evidence of nm23-H1 gene alteration or alterations in Rb protein levels in endometrial carcinoma, high expression of p53 protein was sporadically identified in biopsy specimens of atypical hyperplasia and frequently found in endometrioid carcinomas. Determination of p53 expression in combination with the presence or absence of squamous differentiation and nuclear grade in biopsy material may help predict spread of endometrioid carcinoma outside the uterus and facilitate therapeutic planning before hysterectomy.

Cytokine therapeutics: lessons from interferon alpha

Cytokines are soluble proteins that allow for communication between cells and the external environment. Interferon (IFN) alpha, the first cytokine to be produced by recombinant DNA technology, has emerged as an important regulator of growth and differentiation, affecting cellular communication and signal transduction pathways as well as immunological control. This review focuses on the biological and clinical activities of the cytokine. Originally discovered as an antiviral substance, the efficacy of IFN-alpha in malignant, viral, immunological, angiogenic, inflammatory, and fibrotic diseases suggests a spectrum of interrelated pathophysiologies. The principles learned from in vivo studies will be discussed, particularly hairy cell leukemia, chronic myelogenous leukemia, certain angiogenic diseases, and hepatitis. After the surprising discovery of activity in a rare B-cell neoplasm, IFN-alpha emerged as a prototypic tumor suppressor protein that represses the clinical tumorigenic phenotype in some malignancies capable of differentiation. Regulatory agencies throughout the world have approved IFN-alpha for treatment of 13 malignant and viral disorders. The principles established with this cytokine serve as a paradigm for future development of natural proteins for human disease.

Analysis of chromosome 22 loci in meningioma. Alterations in the leukemia inhibitory factor (LIF) locus

Meningiomas are typically benign tumors arising from arachnoidal cells at the base of the brain. Meningioma is thought to result from the loss or inactivation of a putative tumor suppressor gene located on chromosome 22. We analyzed a set of meningioma DNA specimens by Southern blot hybridization with chromosome 22-specific probes and by PCR using oligomer primers and probes specific to the leukemia inhibitory factor (LIF) gene. Southern analysis suggested that a subset of our specimens are monosomic for 22q11-qter and may have lost one entire copy of chromosome 22. The gene(s) involved in the etiology of meningioma has been localized to 22q11.2-12.3. The locus encoding LIF, a factor that affects the differentiation and proliferation of numerous cell types, has also been localized to this region, at 22q12.1-12.2. The partial overlap of these loci, coupled with the known involvement of the LIF gene product in growth and differentiation, suggested that the LIF locus may be associated with the meningioma defect. We have examined the LIF locus in meningioma specimens at the molecular level by PCR, and by DNA and RNA gel-blot hybridizations. Alterations in the structure and/or expression of the LIF locus were detected in several specimens, including the subset that were shown to be monosomic for 22q. All of our tumor specimens were shown to be undermethylated at the LIF locus relative to constitutional DNA from the same patients. Sequence analysis of LIF cDNA from a meningioma revealed the existence of a novel, alternatively spliced LIF mRNA. These results suggest that the LIF gene may be near the putative tumor suppressor locus associated with the development of this phenotype.

What's new in breast cancer? Molecular perspectives of cancer development and the role of the oncogene c-erbB-2 in prognosis and disease

The oncogene c-erbB-2 is frequently amplified in human breast carcinoma. The c-erbB-2 gene is present as a single copy in normal cells, and has been mapped to chromosome 17 in the region 17q 12-21.32. c-erbB-2 encodes a transmembrane glycoprotein known as p185. The intracellular component of p185 has tyrosine kinase activity; the extracellular domain has a structure resembling a growth factor receptor. c-erbB-2 amplification, p185 overexpression and levels of transcribed c-erbB-2 specific messenger RNA have been studied in a large number of breast carcinomas using a variety of techniques. In general, overexpression of p185 oncoprotein reflects various levels of DNA amplification, though in some cases amplification can be detected in the absence of overexpression of p185 and similarly overexpression of p185 can be present without detectable levels of c-erbB-2 amplification. This findings suggests that multiple mechanisms may be responsible for overexpression. c-erbB-2 amplification and/or overexpression occurs in almost all cases of high grade duct carcinoma in-situ, but has been reported in only 10%-40% of infiltrating duct carcinoma. c-erbB-2 amplification or overexpression occurs rarely in invasive lobular carcinoma, and has not been detected in ductal or lobular epithelial hyperplasia, or in atypical ductal or atypical lobular hyperplasia. It is generally believed that c-erbB-2 amplification/overexpression is an important independent prognostic indicator in breast carcinoma, identifying a subset of patients with poor prognosis tumours, particularly if axillary node metasases are present. However, many unanswered questions remain regarding c-erbB-2 and its role in breast cancer development and progression. The causes of c-erbB-2 amplification are unknown. There is no evidence of mutations in the human gene which might cause amplification or overexpression. The significance of the differences in levels of c-erbB-2 amplification/overexpression in in-situ duct carcinoma and associated invasive duct carcinoma has not been established. Amplification or overexpression have not been reported in atypical duct hyperplasia, a proposed precursor of duct carcinoma in-situ, yet overexpression occurs almost always in high grade duct carcinoma in-situ. c-erbB-2 may play a critical role in the development of a clonal in-situ, proliferation of high histological grade, yet does not obviously influence the acquisition of an invasive phenotype. We would postulated that this instability in amplification/overexpression is of biological significance, and if better understood may aid in the study of progression of human breast carcinoma.

Cell lines derived from ultraviolet radiation-induced benign melanocytic nevi in Monodelphis domestica exhibit cytogenetic aneuploidy

The gray short-tailed opossum, Monodelphis domestica, develops dermal melanocytic nevi (MN) after long-term chronic exposure to UVB (midwavelength ultraviolet radiation) alone. We developed cell lines from six UVB-induced dermal benign melanocytic lesion biopsies. One of the MN was determined histologically to be a benign melanoma (BM), whereas the remainder were benign melanocytic hyperplasias (MH). The cell lines were not tumorigenic when injected subcutaneously into athymic nude mice. Protein extracts prepared from these cell lines were analyzed electrophoretically on polyacrylamide gels and protease zymograms in preliminary attempts to identify protein and protease markers for pathogenesis. Cytogenetic analyses showed that half (three of six) of the MN cell lines exhibited aneuploidy involving extra copies of chromosomes 3, 5, 7, and/or 8. This result suggests that nonrandom aneuploidy can be an early event in chronic UVB induction of benign dermal melanocytic lesions. Karyotyping also showed a centromeric variant of chromosome 7 in some animals, which was confirmed to be constitutional. These Monodelphis cell lines will be valuable reagents for future studies of UVB-induced damage to mammalian skin.

Chromosome 7 suppresses indefinite division of nontumorigenic immortalized human fibroblast cell lines KMST-6 and SUSM-1

Using nontumorigenic immortalized human cell lines KMST-6 (KMST) and SUSM-1 (SUSM), we attempted to identify the chromosome that carries a putative senescence-related gene(s). These cell lines are the only ones that have been established independently from normal human diploid fibroblasts following in vitro mutagenesis. We first examined restriction fragment length polymorphisms on each chromosome of these immortalized cell lines and their parental cell lines and found specific chromosomal alterations common to these cell lines (a loss of heterozygosity in KMST and a deletion in SUSM) on the long arm of chromosome 7. In addition to these, we also found that introduction of chromosome 7 into these cell lines by means of microcell fusion resulted in the cessation of cell division, giving rise to cells resembling cells in senescence. Introduction of other chromosomes, such as chromosomes 1 and 11, on which losses of heterozygosity were also detected in one of the cell lines (KMST), to either KMST or SUSM cells or of chromosome 7 to several tumor-derived cell lines had no effect on their division potential. These results strongly suggest that a gene(s) affecting limited-division potential or senescence of normal human fibroblasts is located on chromosome 7, probably at the long arm of the chromosome, representing the first case in which a specific chromosome reverses the immortal phenotype of otherwise normal human cell lines.

Chromosome 7 suppresses indefinite division of nontumorigenic immortalized human fibroblast cell lines KMST-6 and SUSM-1

Using nontumorigenic immortalized human cell lines KMST-6 (KMST) and SUSM-1 (SUSM), we attempted to identify the chromosome that carries a putative senescence-related gene(s). These cell lines are the only ones that have been established independently from normal human diploid fibroblasts following in vitro mutagenesis. We first examined restriction fragment length polymorphisms on each chromosome of these immortalized cell lines and their parental cell lines and found specific chromosomal alterations common to these cell lines (a loss of heterozygosity in KMST and a deletion in SUSM) on the long arm of chromosome 7. In addition to these, we also found that introduction of chromosome 7 into these cell lines by means of microcell fusion resulted in the cessation of cell division, giving rise to cells resembling cells in senescence. Introduction of other chromosomes, such as chromosomes 1 and 11, on which losses of heterozygosity were also detected in one of the cell lines (KMST), to either KMST or SUSM cells or of chromosome 7 to several tumor-derived cell lines had no effect on their division potential. These results strongly suggest that a gene(s) affecting limited-division potential or senescence of normal human fibroblasts is located on chromosome 7, probably at the long arm of the chromosome, representing the first case in which a specific chromosome reverses the immortal phenotype of otherwise normal human cell lines.

Caffeine enhanced measurement of mutagenesis by low levels of gamma-irradiation in human lymphocytes

The well-known action of caffeine in synergizing mutagenesis (including chromosome aberrations) of agents like ionizing radiation by inhibition of cellular repair processes has been incorporated into a rapid procedure for detection of mutagenicity with high sensitivity. Effects of 5-10 rads of gamma-irradiation, which approximate the human lifetime dose accumulation from background radiation, can be detected in a two-day procedure using an immortalized human WBC culture. Chromosomally visible lesions are scored on cells incubated for 2 h after irradiation in the presence and absence of 1.0 mg/ml of caffeine. An eightfold amplification of scorable lesions is achieved over the action of radiation alone. This approach provides a closer approximation to absolute mutagenicity unmitigated by repair processes, which can vary in different situations. It is proposed that mutagenesis testing of this kind, using caffeine or other repair-inhibitory agents, be employed to identify mutagens in their effective concentrations to which human populations may be exposed; to detect agents such as caffeine that may synergize mutagenic actions and pose epidemiologic threats; and to discover effective anti-mutagens. Information derived from the use of such procedures may help prevent cancer and newly acquired genetic disease.

Absence of p53 mutations in childhood central nervous system primitive neuroectodermal tumors

The primitive neuroectodermal tumor of the central nervous system is one of a number of tumors in which deletions on chromosome 17p have been identified. The tumor suppressor gene, p53, is located in the region of the deletion. To determine if the p53 gene is involved in the development of primitive neuroectodermal tumors, deoxyribonucleic acid (DNA) blot analysis, ribonucleic acid blot analysis, and p53 complementary DNA sequencing were performed on 34 primitive neuroectodermal tumors removed from children. No rearrangement in the gene was detected in 21 tumors. The p53 messenger ribonucleic acid was of the expected size in all 18 tumors for which ribonucleic acid was available. Sequencing of p53 Exons 5 through 9 revealed a mutation in the cell line DAOY and in only 1 of 14 tumors examined. A DNA rearrangement was detected in the DNA from one tumor with a probe mapping to the distal portion of 17p. Taken together, these data suggest that the p53 gene is not involved in the development of most primitive neuroectodermal tumors. In addition, a gene of interest may be present on distal 17p.