Tumor suppressor genes: the puzzle and the promise

Alterations of the p53 gene in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a malignancy which is consistently associated with the Epstein-Barr virus (EBV). The structure of the EBV genome in NPC suggests that NPC is a clonal proliferation of epithelial cells which emerges after EBV infection. The disease develops with high incidence in specific populations in discrete geographic locations, implicating possible genetic or environmental cofactors. Mutations of the p53 gene are among the most frequent genetic changes found in a large variety of human tumors. Mutations in p53 have been shown to abrogate the suppressor function of wild-type p53 and thus contribute to the transformed phenotype. To determine if mutation in p53 participates in the development of the malignant clone in NPC, the structure and sequence of p53 in 42 primary, metastatic, and nude mouse-passaged NPC specimens was analyzed. A high frequency (6 of 9) of mutations was detected in the nude mouse-passaged tumors, while only 2 of 15 metastatic and 0 of the 18 primary tumors harbored mutant p53. The p53 mutations included single-point mutations and more extensive changes such as frame shifts, deletion, duplication, or complete loss of coding sequences. These data indicate that alterations of the p53 gene are unlikely to be involved in the initial genetic events leading to the clonal outgrowth in NPC. However, although it is a rare NPC which can be established in nude mice, this growth advantage appears to be conferred on tumors bearing a mutant p53.

Evolutionary somatic cell changes in cervical tumour progression quantitatively evaluated with morphological, histochemical and kinetic parameters

The somatic cell changes which characterise malignancy evolution in human cervical preneoplastic and neoplastic lesions have been assessed on histological sections by means of a computerised image analyser. Many features have been simultaneously measured on each cell of the lesions studied, and the following results have been obtained: Some features, mainly kinetic, show continuously increasing values which express changes correlated to the increasing malignancy; other features, especially related to nuclear atypia, cellular heterogeneity and the degree of aneuploidy, have values dropping at the level of early stromal infiltration, which can be morphometrically characterised as composed of relatively homogeneous phenotypes; these features seem to express the degree of genetic instability and relate to the evolutionary somatic cell changes; tumour progression evolves through sequential discontinuous steps, each of them characterised by specific phenotypical features of the neoplastic cell population; the neoplastic cells in the foci of early stromal infiltration and vascular invasion, phenotypically more homogeneous than the parent cell populations of carcinoma in situ and infiltrating carcinoma, seem to possess a greater genetic stability.

Telomeric associations evolving to ring chromosomes in a recurrent pleomorphic xanthoastrocytoma

Telomeric associations observed in a recurrent untreated pleomorphic xanthoastrocytoma were apparently the primary cytogenetic events that evolved by fusion and breakage events, resulting in subclones with ring chromosomes. The telomeric fusions between chromosomes 15pter and 20qter, and between an extra copy of the long arm of chromosome 1 and chromosome 22qter, evolved in a stepwise fashion to ring chromosomes 20 and 22. The findings in this tumor demonstrate that telomeric association is one mechanism that can initiate chromosome instability by generating subclones with unstable chromosome intermediates and result in ring chromosomes and subsequent chromosome loss.

A novel blocker-PCR method for detection of rare mutant alleles in the presence of an excess amount of normal DNA

A novel polymerase chain reaction method was developed to preferentially amplify a segment of DNA containing a base substitution mutation. This technique uses a pair of dideoxynucleotide-labeled oligonucleotides (18 mers) of normal sequences as blockers located between the two primers. By virtue of a subtle difference in the melting temperature between the blocker-normal DNA and blocker-mutant DNA hybrids, the method allows preferential amplification of the mutant DNA. We used the human N-ras gene as a model. Two different types of N-ras mutations could be effectively amplified when they were present with an excess amount of normal DNA at a ratio of 1:10(3). Furthermore, the sensitivity was increased 10-fold by using single strand conformation polymorphism analysis for the amplified products, and mutant DNA was detected in the presence of a 10(4) times excess amount of normal DNA.

Expression of interleukin 1-inducible genes and production of interleukin 1 by aging human fibroblasts

The interleukin 1 (IL-1)-inducible mRNAs for plasminogen activator inhibitor type 2, manganese superoxide dismutase, and urokinase are overexpressed in old (greater than 70% of life-span completed) but not in young (less than 40% of life-span completed) human foreskin fibroblasts. Furthermore, the activity of this superoxide dismutase is greater in old than in young fibroblasts. IL-1 beta mRNA is detected by Northern blot analysis in old fibroblasts and its expression is further enhanced by a treatment with IL-1 alpha. IL-1 alpha and IL-1 beta mRNAs are detected in old foreskin and lung fibroblasts by a sensitive reverse transcription-PCR assay. IL-1 mRNA is consistently expressed after fibroblasts have completed 85% of their in vitro life-span; an assay with specific antibodies shows that IL-1 alpha is present in these fibroblasts. Prolonged treatment with IL-1 receptor antagonist decreases the levels of IL-1 alpha and of IL-1 alpha and IL-1 beta mRNAs. This observation suggests that IL-1 receptor antagonist inhibits an autocrine loop responsible for IL-1 expression. IL-1 mRNA accumulates in young fibroblasts treated with cycloheximide, suggesting that it is transcribed but unstable in these cells; accumulation of IL-1 mRNA in old fibroblasts may be due at least in part to increased stability. IL-1 alpha stimulates DNA synthesis in young fibroblasts but has progressively less effect as the cells age in culture. These data indicate that IL-1 is "constitutively" produced by aging fibroblasts and that IL-1 induces the expression of specific proteins in these cells. The mechanism for this constitutive production of IL-1 is explored in this paper.

Suppression of transformed phenotype in hybrids of v-fgr and v-raf transformed rat-1 cells with rat embryonic fibroblasts is due to transcriptional inactivation of viral oncogenes

Rat-1 cells that had been transformed to tumorigenicity by transfection with the retroviral oncogenes v-raf from 3611-murine sarcoma virus, or v-fgr from Gardner-Rasheed feline sarcoma virus were fused with rat embryonic fibroblasts at an early passage. In both fusion experiments hybrid cells were isolated that exhibited normal morphology, anchorage requirement for proliferation, and either no tumorigenicity (v-fgr) or extended latency periods for tumor growth (v-raf) in nude mice. Transcription of viral oncogenes is drastically reduced in hybrid cells (at least 30-fold compared to their transformed parental cells), while the half-life of the corresponding transcripts is not effected. In the chromatin of hybrid cells the integrated retroviral oncogenes are as sensitive to degradation with pancreatic DNase I as the endogenous actin gene. Thus the observed down regulation of proviral transcript levels does not correlate with changes in chromatin structure. We conclude that in hybrids of (v-fgr)- and (v-raf)-transformed Rat-1 cells with embryonic fibroblasts, transcription of the retroviral oncogenes appears to be repressed by trans-acting factors of the normal parental cell.

Reciprocal regulation of adipogenesis by Myc and C/EBP alpha

3T3-L1 adipoblasts that express large amounts of c-Myc cannot terminally differentiate, raising the possibility that Myc inhibits the expression of genes that promote adipogenesis. The CCAAT/enhancer binding protein (C/EBP alpha) is induced during 3T3-L1 adipogenesis when cells commit to the differentiation pathway. Transfection of 3T3-L1 adipoblasts with the gene that encodes C/EBP alpha caused overt expression of the adipocyte morphology. Expression of Myc prohibited the normal induction of C/EBP alpha and prevented adipogenesis. Enforced expression of C/EBP alpha overcame the Myc-induced block to differentiation. These results provide a molecular basis for the regulation of adipogenesis and implicate Myc and C/EBP alpha as pivotal controlling elements.

Down-regulation of a member of the S100 gene family in mammary carcinoma cells and reexpression by azadeoxycytidine treatment

A cDNA clone, designated CaN19 (originally called clone 19), isolated by subtractive hybridization, contains sequences that are preferentially expressed in normal mammary epithelial cells but not in breast tumor cells. Comparison of its deduced amino acid sequence with sequences in the GenBank data base revealed similarity with the S100 protein family, a group of small Ca(2+)-binding modulator proteins involved in cell cycle progression and cell differentiation. CaN19 expression is down-regulated in normal cells by A23187, a calcium ionophore, suggesting that its regulation is calcium-dependent. We have assigned CaN19 to human chromosome 1q21-q24, a region containing four other S100-related genes. In contrast to CaN19 mRNA expression, most members of the S100 protein family are activated or overexpressed in tumor cells. Synchronization experiments by growth-factor deprivation demonstrated a biphasic induction of CaN19 expression in normal cells, approximately 2-fold in early G1 phase and another 2- to 3-fold at the G1/S boundary. Exposure of mammary tumor cells to 5-aza-2'-deoxycytidine, an inhibitor of DNA methylation, reactivated the expression of CaN19 mRNA.

Human chromosome 11 contains two different growth suppressor genes for embryonal rhabdomyosarcoma

The identification of acquired homozygosity in human cancers implies locations of tumor suppressor genes without providing functional evidence. The localization of a defect in embryonal rhabdomyosarcomas to chromosomal region 11p15 provides one such example. In this report, we show that transfer of a normal human chromosome 11 into an embryonal rhabdomyosarcoma cell line elicited a dramatic loss of the proliferative capacity of the transferrants. Indeed, the majority of the viable microcell hybrids had either eliminated genetic information on the short arm of the transferred chromosome 11 or increased the copy number of the rhabdomyosarcoma-derived chromosomes 11. Cells that possessed only the long arm of chromosome 11 also demonstrated a decreased growth rate. In contrast, all microcell hybrids retained the ability to form tumors upon inoculation into animals. These functional data support molecular studies indicating loss of genetic information on chromosome 11p15 during the development of embryonal rhabdomyosarcoma. In addition, our studies demonstrate the existence of a second gene on the long arm, previously unrecognized by molecular analyses, which negatively regulates the growth of embryonal rhabdomyosarcoma cell lines.

A chromosome 17:7 translocation is associated with a hepatitis B virus DNA integration in human hepatocellular carcinoma DNA

Chronic hepatitis B virus infection is often associated with major structural rearrangements of both the integrated viral DNA and the associated cellular sequences. We present here the structure of a single-copy hepatitis B virus insert cloned from human hepatocellular carcinoma DNA recently reported to encode a novel transcriptional trans-activator function. The hepatitis B virus portion of the clone consists of two colinear fragments covering the X gene with its promoter and enhancer (nucleotides 717 to 1796) and a 3' truncated pre-S/S gene (nucleotides 2703 to 423). The lack of the entire pre-C/C gene caused a fusion of the 3' end of the X gene with sequences upstream from the pre-S gene. The structure of the integrated viral DNA fragments suggests insertion of hepatitis B virus replication intermediates into cellular DNA and subsequent recombination between these primary integrations to generate the final structure of the clone. The 5' and 3' cellular flanking sequences mapped to the centromeric alpha-satellite DNA of chromosome 17 and to the short arm of chromosome 7 (p14-pter), respectively, indicating that chromosomal translocation was associated with the hepatitis B virus DNA integration. Because this is the fourth case reported in which hepatitis B virus-associated rearrangements have affected chromosome 17, it is conceivable that a loss of important cellular genes (such as the p53 antioncogene on chromosome 17) may be a crucial step in hepatitis B virus-related hepatocarcinogenesis.

Cytogenetic comparison of two poorly differentiated human lung squamous cell carcinoma lines

This paper presents a cytogenetic analysis of two established but early-passage (passages 5 and 18) cell lines derived from histologically similar, poorly differentiated lymph node metastases of squamous cell carcinoma of the lung. The cell lines showed 3 shared marker chromosomes, del(1)(q11), del(2)(p11.1) and del(2)(q11.1). One of the lines (DLKP) had 8 additional markers including structural rearrangements such as translocations and isochromosomes. Five additional markers (including two deletions of chromosome 3) were found in DLRP. A notable feature of DLRP was the high incidence of telomeric association evident in the majority of metaphase plates. Over-representation of chromosome 7 was a characteristic feature of metaphases derived from DLKP, and identification of i(21q) in this cell line was an unusual finding. The results indicate significant cytogenetic heterogeneity between these early-passage cell lines derived from two apparently histologically similar tumors.

Neoplastic expression in murine cells induced by halogenated hydrocarbons

The neoplastic expression in mouse embryo fibroblasts exposed to 1,2-dibromoethane and its chloroanalogue, 1,2-dichloroethane in vitro, was examined. Both substances are widely used as fumigants for carpet and upholstery, as gasoline additives, and as organic solvents. Both are known to be highly toxic, mutagenic, and carcinogenic agents. C3H10T1/2 cells treated with these haloalkanes exhibited altered morphology and were selected further by cloning in soft agar. Soft agar clones were found to induce a 100% multitumor occurrence in the nude mouse model. These results suggest that this pair of mutagens have altered the normal phenotype of mouse embryo cells, and these cells have become neoplastic. These neoplastic cell lines will be useful as an in vitro model to study the role of genetic changes in the transformation processes induced by halogenated hydrocarbons.

Somatic mutations and human breast cancer. A status report

A systematic study of primary human breast tumor DNA demonstrated that three proto-oncogenes or regions of the genome (c-myc, int-2, and c-erbB2) are frequently amplified and that there is loss of heterozygosity (LOH) on chromosomes 1p(37%), 1q(20%), 3p(30%), 7(41%), 11p(20%), 13q(30%), 17p(49%), 17q(29%), and 18q(34%). Specific subsets of tumors can be defined based on the particular collection of mutations they contain. For instance, LOH on chromosomes 11p, 17p, and 18q frequently occurs in the same tumor. A search for putative tumor suppressor genes within the regions of the genome affected by LOH has been started. In a comprehensive molecular analysis of the p53 gene on chromosome 17p, 46% of the tumors contained a point mutation in the p53 gene.

Frequent deletions in nine newly immortal human cell lines

Nine newly immortal lines of human fibroblasts transfected with SV40 T antigen were examined for recurrent chromosome losses. In order of decreasing frequency, all nine lines had three or more of the following minimal deletions specifically associated with the immortalization event: del(6)(q21), del(3)(p24), del(1)(p34), del(4)(p25), del(5)(p14), del(11)(p11), del(11)(q14), del(12)(p12), and del(14)(p?). Many other chromosome changes were not clearly associated with immortalization, but were acquired during other stages of this multistep model of neoplastic transformation. We propose that these chromosome loci associated with immortalization are candidates for the location of genes involved in cellular senescence.

The association of astrocytoma and pituitary adenoma in a patient with alcaptonuria

A female patient with a juvenile pilocytic astrocytoma and a pituitary adenoma is described. The patient also has alcaptonuria, a rare inborn error of metabolism with autosomal recessive mode of inheritance. The association of these three disorders has never been reported previously. The possible existence of a common genetic factor in the development of both tumors and alcaptonuria is discussed.

Cancer volume and site of origin of adenocarcinoma in the prostate: relationship to local and distant spread

Biologic aggressive behavior in adenocarcinoma of the prostate is proposed to be a direct function of cancer volume. In an autopsy series, distant metastasis was found only in cancers that had both volume greater than 5 cc and areas of poor differentiation (Gleason grades 4 and 5). In subsequent study of over 200 radical prostatectomy specimens, cancers were found to originate both in the peripheral zone (PZ) and in the normally small anteromedial transition zone (TZ) where benign nodular hyperplasia also develops. Anatomic TZ and PZ cancers were nearly equivalent to clinical stage A and B cancers, respectively. Transition zone cancers showed much less capsule penetration and seminal vesicle invasion than PZ cancers of comparable volume because the TZ boundary provided a barrier to cancer spread through the PZ. In PZ carcinomas, capsule penetration depended largely on facilitated spread along perineural spaces, and its distribution was determined by the location of superior and inferior nerve pedicles. Capsule penetration, seminal vesicle invasion, and positive surgical margins were all strongly correlated with cancer volume. Tumors smaller than 4 cc had all morphologic variables favorable; tumors larger than 12 cc tended to have all variables unfavorable. Lymph node metastasis in radical prostatectomy cases was most strongly predicted by a combination of cancer volume plus percentage of high-grade tumor. Cancers with more than 3.2 cc of grade 4 and/or 5 component showed a 100-fold increase in proportion of cases with nodal spread.

Predominance of chromosome 5 deletions in myeloid neoplasia associated with solid tumors managed by surgical excision

To assess potential differences in genetic predisposition to myeloid neoplasia, we evaluated the karyotypes and reviewed results of cytogenetic studies on bone marrow specimens from six patients with myelodysplastic syndrome, or acute myeloid leukemia, and a history of solid tumor managed solely by surgical resection. Structural or numerical deletions of chromosome 5 were identified in each of four patients with abnormal marrow karyotypes. Constitutional karyotypes were normal in two patients studied with clonal marrow chromosome abnormalities. Review of previously reported cases of myeloid neoplasia following resection of solid tumors disclosed a preponderance of chromosome 5 deletions. Predisposition to specific chromosome loss may influence genetic expression of disease in solid tumor patients developing hematologic malignancy.

Chromosome 1 in human colorectal tumors. Cytogenetic research on structural changes and their significance

The significance of short and long arm anomalies of chromosome 1 was investigated in 55 colorectal tumors comprising 41 carcinomas and 14 adenomas. The tumors were at various stages of transformation from adenoma to carcinoma. Our investigation was prompted by the observation of a p32-pter deletion on the short arm of chromosome 1 in a case of benign tubulovillous adenoma with mild dysplasia, as well as by frequent reports that chromosome 1 is involved in many neoplastic processes. Long arm anomalies were found in seven of the 41 carcinomas, six of which were in stage B2, and short arm anomalies in ten carcinomas at various stages. Three of the adenomas exhibited chromosome 1 anomalies, which in one case comprised a 1p32-pter deletion only. Overall, short arm anomalies especially concerned the p32-36 region. These results suggest that the cytogenetic anomalies respectively located on the short and long arms of chromosome 1 should be considered separately. Damage to the long arm might constitute a late non-specific event, whereas damage to the p32-pter region of the short arm might be involved in triggering colorectal tumor development.

The cell-cell channel in the control of growth

Several lines of evidence indicate that the cell-cell channels in gap junction are conduits for growth-regulating signals. Experimental upregulation of the channels by retinoids causes inhibition of cellular growth and, conversely, their downregulation by oncogenes, e.g. activated src, stimulates growth. In either direction, the extent of growth correlates tightly with the degree of communication. Cogent evidence of the channel's function in growth regulation is now on hand: incorporation of a channel-protein gene into the genome of a transformed communication-deficient cell line normalizes communication and growth. The current data conform to a model of growth control with discrete regulatory centers.

Deficiency of 5'-deoxy-5'-methylthioadenosine phosphorylase activity in malignancy. Absence of the protein in human enzyme-deficient cell lines

The absence of 5'-deoxy-5'-methylthioadenosine phosphorylase (MTAase) activity in malignant cells, and the putative localization of its gene, suggest that this enzyme deficiency might be due to a genomic alteration also involving a tumour-suppressor gene. We studied the possible occurrence of inactive forms of the protein in two MTAase-negative cell lines, namely K562 and Jurkat, by immunochemical methods. Two highly specific antisera, directed against different epitopes of the phosphorylase [Della Ragione, Oliva, Gragnaniello, Russo, Palumbo & Zappia (1990) J. Biol. Chem. 265, 6241-6246], were used to carry out immunotitration and immunoblotting analyses, as well as to investigate the biosynthesis of the enzyme. No MTAase protein was detected by Western-blotting technique performed under conditions where all the phosphorylase-positive samples gave a clear band at the MTAase subunit molecular mass. No cross-reacting material was observed by a sensitive immunotitration method which permitted the detection of as low as 0.5 ng of protein. Moreover, the results obtained by [35S]methionine-labelling experiments ruled out phosphorylase biosynthesis in the negative cell lines. Altogether, these data suggest that an alteration at the gene level hampering the specific mRNA biosynthesis or resulting in an untranslatable mRNA is the cause of the enzyme deficiency in the MTAase-negative cell lines studied.

Differential retention of tumor- and differentiation-suppressor functions in cells derived from a human squamous cell carcinoma

Three morphologically distinct cell lines--F.2a, V, and B.2--were isolated from a single human squamous cell carcinoma. Although all three cell lines can grow indefinitely in culture, they differ in a number of important transformation-related phenotypes. Only B.2 is strongly tumorigenic when injected into the flanks of nude mice, and only V can efficiently grow in semisolid media. The dominance of these traits was investigated by generating somatic cell hybrids among the three cell lines. F.2a was able to suppress the tumorigenicity of B.2 cells, whereas B.2 inhibited the capacity for anchorage-independent growth of V, the latter trait being a function of the ability of these epithelial cells to differentiate when deprived of support. The influence of exogenously added growth factors was also evaluated. This study indicates that the particular tumor we examined consisted of a heterogeneous population of cells with distinct growth and differentiation capacities.

Association of induction of a fully tumorigenic phenotype in murine radiation-induced T-lymphoma cells with loss of differentiation antigens, gain of CD44, and alterations in p53 protein levels

We investigated the mechanism of radiation induction of murine thymic lymphomas by studying the characteristics of primary x-ray-induced thymic lymphoma (PXTL) cell lines and of their oncogene-induced, progressed progeny. It is widely thought that proto-oncogene alterations are associated with the induction of murine lymphomas; however, few, if any primary murine radiation-induced lymphomas possess (proto-)oncogene alterations. Independently derived cell lines grown directly (i.e., without in vivo transplantation) from thymic lymphomas of irradiated C57BL/6 mice possess the properties of immortalized pre-T cells and lack many of the characteristics of "tumor cells". PXTL cells are poorly tumorigenic upon transplantation, do not clone in methylcellulose cultures, are growth factor dependent and autocrine, and lack consistent chromosome and oncogene abnormalities. However, the thymic lymphomas are malignant and cause the death of each afflicted mouse. PXTL cells expressed two immunologically distinct forms of the tumor suppressor protein p53 that have moderately increased stability (t1/2 = 1 h) when compared with p53 of normal splenic T lymphocytes. Early PXTL cells could progress in vitro to a fully tumorigenic phenotype after infection with retroviruses encoding the c-myc and v-ras oncogenes. Progressed T-lymphoma cells acquired growth factor independence, a highly transplantable and tumorigenic phenotype, and the ability to quantitatively clone in methylcellulose cultures. Progressed lymphoma cells coordinately downregulated the expression of five T-cell differentiation markers, upregulated the expression of CD44 (Pgp-1), and harbored vastly elevated levels of two immunologically distinct forms of p53. Our results suggest that the early thymic lymphomas consist of differentiation-inhibited, immortal pre-T cells that are precursors to progressed, fully tumorigenic T-lymphoma cells.

Indicators of increased breast cancer risk in humans

Specific atypical histological patterns of epithelial hyperplasia (AH) indicate a medically relevant risk of breast cancer development in 5-10% of women with otherwise benign biopsies. This risk is about four times that of similar women, i.e., of the same age and at risk for the same length of time. These relative risks are not stable with time and fall 10-15 years after detection. Absolute risk for invasive breast cancer after AH is about 10% in 10-15 years after biopsy and is most certain for perimenopausal women. Proliferative disease without atypia predicts only a slight elevation of risk with a relative risk (RR) of 1.5 to 2 times that of the general population. There is such a strong interaction between family history and AH that it is relevant to consider women with atypical hyperplasia who have a positive family history (FH) of breast cancer separately from those who do not. The absolute risk of breast cancer development in women with AH without a FH was 8% in 10 years (RR about 4), whereas those with a positive family history experienced a risk of about 20% at 15 years (RR of about 10). This interaction of AH and FH has also been observed in other recent studies. Low replacement doses of conjugated estrogen after menopause do not further elevate risk beyond that identified by histology.(ABSTRACT TRUNCATED AT 250 WORDS)

Possible cellular and molecular mechanisms for asbestos carcinogenicity

Asbestos fibers may exert their carcinogenic effects on mesothelial cells and bronchial epithelial cells by direct and indirect mechanisms. Direct effects can occur following the physical interaction of fibers with target cells or by the generation of free radicals from the fiber surface; indirect effects, following the interaction of fibers with inflammatory cells can result in the production of cellular mediators such as cytokines and various reactive oxygen species. As a result, target cells may be induced to proliferate and/or sustain genetic alterations, which lead to tumor development.

Genetic changes in mammalian cells transformed by helium ions

Midterm Syrian Hamster embryo (SHE) cells were employed to study high LET-radiation induced tumorigenesis. Normal SHE cells (secondary passage) were irradiated with accelerated helium ions at an incident energy of 22 MeV/u (9-10 keV/micrometer). Transformed clones were isolated after growth in soft agar of cells obtained from the foci of the initial monolayer plated postirradiation. To study the progression process of malignant transformation, the transformed clones were followed by monolayer subculturing for prolonged periods of time. Subsequently, neoplasia tests in nude mice were done. In this work, however, we have focused on karyotypic changes in the banding patterns of the chromosomes during the early part of the progressive process of cell transformation for helium ion-induced transformed cells.

Molecular mechanisms of spontaneous and induced loss of heterozygosity in human cells in vitro

The human TK6 lymphoblast cell line is heteroallelic at the thymidine kinase (TK) locus, with one functional and one nonfunctional allele. Cells that have undergone loss of heterozygosity (LOH) at TK can be selected and cloned in an in vitro assay. In order to study the extent of LOH, we have analyzed a total of 166 thymidine kinase-deficient mutants that arose either spontaneously or following induction by X-ray or ethyl methane sulfonate (EMS) using DNA probes in and around the TK gene on chromosome 17. Two distinct groups of mutants with different doubling times were identified. Among slow-growth mutants, the predominant change for both spontaneous and induced mutants was LOH that generally extended through the entire TK gene to both proximal and distal markers on 17q. While the majority of both spontaneous and X-ray-induced normal-growth mutants showed LOH, this was considerably more localized in scale for X-ray-induced mutants, which rarely involved the distal marker. LOH was rare among EMS-induced normal-growth mutants. LOH was never observed with a 17p marker, indicating that nondisjunctional events were not involved in any of the mutant clones examined. Densitometric analysis of the LOH mutants indicated mitotic recombination was a likely mechanism in more than half the spontaneous LOH mutants in both groups, whereas most induced mutants appeared to arise from simple deletions.

Multistage carcinogenesis in mouse skin

The mouse skin model of multistage carcinogenesis has for many years provided a conceptual framework for studying carcinogenesis mechanisms and potential means for inhibiting specific stages of carcinogenesis. The process of skin carcinogenesis involves the stepwise accumulation of genetic change ultimately leading to malignancy. Initiation, the first step in multistage skin carcinogenesis involves carcinogen-induced genetic changes. A target gene identified for some skin tumor initiators is c-Ha-ras. The second step, the promotion stage, involves processes whereby initiated cells undergo selective clonal expansion to form visible premalignant lesions termed papillomas. The process of tumor promotion involves the production and maintenance of a specific and chronic hyperplasia characterized by a sustained cellular proliferation of epidermal cells. These changes are believed to result from epigenetic mechanisms such as activation of the cellular receptor, protein kinase C, by some classes of tumor promoters. The progression stage involves the conversion of papillomas to malignant tumors, squamous cell carcinomas. The accumulation of additional genetic changes in cells comprising papillomas has been correlated with tumor progression, including trisomies of chromosomes 6 and 7 and loss of heterozygosity. The current review focuses on the mechanisms involved in multistage skin carcinogenesis, a summary of known inhibitors of specific stages and their proposed mechanisms of action, and the relevance of this model system to human cancer.

Oncogenes in gynecological tumors

Evidence is increasing that proto-oncogenes and cancer suppressor genes are involved in the development and/or progression of gynecological malignancies. While histopathologic examination remains an indispensable tool of the surgical pathologist in the diagnosis and evaluation of patients with gynecological malignancies, the advancement to technology and the development of new knowledge regarding neoplastic transformation are providing a basis for new opportunities to improve patients care. These new opportunities will depend on the use of the skills and reagents developed in the basic medical science laboratories. Thus, it is important for those in the field of diagnostic pathology to begin to acquire a knowledge of proto-oncogenes and cancer suppressor genes as well as a basic understanding of the techniques used to detect and evaluate them.

Flow cytometric measurements of somatic cell mutations in Thorotrast patients

Exposure to ionizing radiation has long been well-recognized as a risk factor for cancer development. Since ionizing radiation can induce mutations, an accurate way of measuring somatic mutation frequencies could be a useful tool for evaluating cancer risks. In the present study, we have examined in vivo somatic mutation frequencies at the erythrocyte glycophorin A (GPA) and T-cell receptor (TCR) loci in 18 Thorotrast patients who have been continuously irradiated with alpha-particles emitted from the internal deposition of thorium dioxide and who thus have increased risks of certain malignant tumors. When compared with controls, the results showed a significantly higher frequency of mutants at the lymphocyte TCR loci but not at the erythrocyte GPA loci in the Thorotrast patients. The discrepancy between the results of the two assays is discussed.

Growth factor requirements of human colorectal tumour cells: relations to cellular differentiation

Human colorectal tumour lines that exhibit different degrees of differentiation were studied to define their growth requirements. The poorly differentiated cell lines SW620, SW480, SW48 and SW837 proliferated in Dulbecco's modified Eagle's medium without exogenously added growth factors. In contrast, the moderately differentiated cell lines SW1222, HT29, PC/JW and LS174T proliferated only in medium supplemented with growth factor. SW1222 and HT29 cells required transferrin for growth, which was improved by other growth-promoting factors including epidermal growth factor (SW1222) and sodium selenite (HT29). PC/JW and LS174T required both insulin and transferrin for optimal growth. The tumour cell lines could be passaged continuously in serum-free medium supplemented with growth factor and in some cases they grew better than in serum-supplemented medium. The serum-free growth conditions should prove useful for studies on differentiation in colorectal cell lines and their interactions with growth factors.

Loss of constitutional heterozygosity on chromosome 5q in hepatocellular carcinoma without cirrhosis

Suppressor gene loci involved in the development of hepatocellular carcinoma (HCC) have not been fully identified. The aim of this study was to look for consistent allele loss, or loss of heterozygosity (LOH), in HCC which might represent such gene loci. We have prepared DNA from tumour and non-tumour material from 16 patients with HCC (nine with and seven without liver cirrhosis). Tumour DNA was compared with non-tumour DNA by Southern analysis performed with a panel of 22 probes recognising restriction fragment length polymorphisms assigned to chromosomes 1, 4, 5, 7, 9, 11, 12, 13, 14, 16, 17, 18 and 20. Non-tumour DNA from five of the seven patients with HCC without cirrhosis was heterozygous with the probe Lambda MS8 (5q35-qter), and in all five there was LOH in tumour DNA. Probes for other regions of chromosome 5 have as yet shown no LOH in this group of patients. Cirrhotic HCC patients exhibited LOH on chromosomes 1q and 5p but not in the region 5q35-qter. Both groups of HCC showed LOH on chromosome 17p13. Screening with other probes has not shown any consistent LOH in either group as yet. A comparison of LOH on chromosome 5 in seven patients with colorectal metastasis in the liver showed a different pattern, which suggests that the proposed tumour suppressor gene locus for HCC without cirrhosis on chromosome 5 appears to be distinct from the familial adenomatous polyposis coli gene.

Transgenic models of tumor development

Numerous cancer-prone strains of mice have been created by the introduction of candidate tumor-promoting genes into fertilized eggs. Each transgenic strain is predisposed to develop specific types of tumors, but they usually arise stochastically because of the need for spontaneous mutation of genes that collaborate with the introduced oncogene. These mice are providing insights into the effects of individual oncogenes on cellular proliferation, differentiation, and viability, as well as on oncogene cooperativity. Their predisposed state imposes sensitivity to viral and chemical carcinogenesis, and the mice should prove valuable in tests of potential carcinogens, therapies, and preventive measures.

Tumor suppressor genes

For the past decade, cellular oncogenes have attracted the attention of biologists intent on understanding the molecular origins of cancer. As the present decade unfolds, oncogenes are yielding their place at center stage to a second group of actors, the tumor suppressor genes, which promise to teach us equally important lessons about the molecular mechanisms of cancer pathogenesis.

Monozygotic twins discordant for the major signs of McCune-Albright syndrome

We describe a girl, one of monozygotic (MZ) twins, with endocrine dysfunction with precocious puberty, café-au-lait nevi and polyostotic fibrous dysplasia (PFD), McCune-Albright syndrome (MAS). After treatment with cyproterone acetate for 7 years the precocious puberty and excess growth improved but the bone-age still remain advanced. The co-twin had an advanced bone-age and a small café-au-lait spot, but showed neither endocrinopathy nor fibrous dysplasia of bone. On the basis of the findings in these twins, together with those in previously reported familial cases of MAS, including two pairs of MZ twins, a 2-hit mutation hypothesis is proposed: a dominant mutation may be inherited and leads to PFD in offspring as the primary defect of MAS; the second mutation may occur in somatic cell leading to mosaicism and thus resulting in MAS. This concept explains not only sporadic cases of MAS but also reported familial cases. If we assume that the second mutation occurred in an early somatic division, it would explain the discrepancy of clinical manifestation between MZ twins.

Characterization of the mouse cDNA and gene coding for a hepatocyte growth factor-like protein: expression during development

The cDNA and gene coding for mouse hepatocyte growth factor-like protein (HGF-like protein) were isolated and characterized. The size of the gene from the site of initiation of transcription to the polyadenylation site is 4613 bp in length and is composed of 18 exons separated by 17 intervening sequences. The exons range in size from 36 to 227 bp in length, while the intervening sequences range in size from 78 to 613 bp in length. The site of initiation of transcription was identified by primer extension analysis using total RNA isolated from mouse liver. On the basis of these results, the first exon is 146 bp in length and includes 94 bp of 5'-noncoding sequence. The sequence 5'TATGTG3' is present between 34 and 39 bp upstream of the transcription start site and could potentially be the TATA sequence found for many constitutively expressed eukaryotic genes to be the promoter for RNA polymerase II. The sequence 5'GCAAT3' at -96 to -92 may be the CCAAT sequence responsible for stimulation of transcription of some eukaryotic genes. The same sequences in the Genbank and NBRF databases were homologous to similar regions in the genes coding for both human and mouse HGF-like protein (Han et al., 1991). The acyl-peptide hydrolase gene is 410 bp downstream of the mouse HGF-like protein, but is transcribed from the complementary strand. The mouse cDNA for HGF-like protein codes for a putative protein with the same domain structure as its human homologue with four kringle domains followed by a serine protease-like domain. On the basis of the translated sequence of the cDNA, the mouse HGF-like protein would be 716 amino acids in length with a molecular weight of 80K. There are four potential N-linked carbohydrate attachment sites. The DNA and amino acid sequences of mouse HGF-like protein are compared to the human protein. Overall, the two proteins are about 80% identical with each other. In contrast to mRNA for human HGF-like protein, which is 2.4 and 3.0 kilobases in length in human liver, only the smaller species is seen in mouse and rat liver. The expression pattern of mRNA coding for HGF-like protein during development and in maternal rats was determined by Northern analysis. It is apparent that the majority of mRNA coding for HGF-like protein is expressed in liver. Messenger RNA is also expressed at a lower level in lung, adrenal, and placenta.

Characterization of the DNF15S2 locus on human chromosome 3: identification of a gene coding for four kringle domains with homology to hepatocyte growth factor

A human genomic DNA library was screened by using conditions of reduced stringency with a bovine cDNA probe coding for the kringle domains in prothrombin in order to isolate the human prothrombin gene. Twelve positives were identified, three of which coded for prothrombin (Degen & Davie, 1987). Phage L5 was characterized in more detail because of its strong hybridization to the cDNA probe and its unique restriction map compared to the gene coding for human prothrombin. The gene in L5 was sequenced and found to code for a kringle-containing protein. A human liver cDNA library was screened by using a genomic probe from the gene in L5. cDNAs were isolated that contained sequence identical with regions in the gene in L5. Comparison of the cDNA with the gene indicated that the gene in L5 was composed of 18 exons separated by 17 intervening sequences and is 4690 bp in length. Exons ranged in size from 36 to 242 bp in length while intervening sequences ranged from 77 to 697 bp in length. The putative protein encoded by the gene in L5 contains four kringle domains followed by a serine protease-like domain. This domain structure is identical with that found in hepatocyte growth factor (HGF), although the two proteins are only about 50% identical. On the basis of the similarity of the protein encoded by L5 and HGF, we propose that the putative L5 protein be tentatively called HGF-like protein until a function is identified. The DNA sequence of the gene and cDNA and its translated amino acid sequence were compared against GenBank and NBRF databases. Sequences homologous to DNF15S1 and DNF15S2, human DNF15S2 lung mRNA, and rat acyl-peptide hydrolase were identified in exon 17 to the 3' end of the characterized sequence for the gene. From our results, it is apparent that the gene coding for human HGF-like protein is located at the DNF15S2 locus on human chromosome 3 (3p21). The gene for acyl-peptide hydrolase is 444 bp downstream of the gene coding for HGF-like protein, but on the complementary strand. The DNF15S2 locus has been proposed to code for one or more tumor suppressor genes since this locus is deleted in DNA from small cell lung carcinoma, other lung cancers, renal cell carcinoma, and von Hippel-Lindau syndrome.

Rat chromosome 5 (q22-23) contains elements that control cell morphology and interactions with the extracellular matrix: a study of normal fibroblast x malignant hepatoma cell hybrids

Cell interactions with the extracellular matrix are consistently modified in neoplasia. Malignant transformation has been correlated with modifications in the synthesis and distribution of matrix components and with alterations of cell adhesive properties to these components. A particular class of genes, able to suppress the transformed phenotype in normal cells, may be involved in those phenotypic changes. By studying somatic cell hybrids between mouse hepatoma (BWTG3) cells and normal rat skin fibroblasts (RSF), Islam and co-workers were able to localize a gene or a group of genes controlling anchorage dependence and cell growth in vitro. This (or these) gene(s) was (were) assigned to the q22-23 fragment of rat chromosome 5. In the present study, we compare the morphology and the interactions with the extracellular matrix proteins (laminin, fibronectin, and collagen IV) and the synthesis of these proteins by RSF X BWTG3 hybrid cells that had either retained (BS181p10) or lost (BS181a5) the q22-23 region of rat chromosome 5. Our results suggest that the rat 5q22-23 fragment controls a part of the cell differentiation program including morphology, attachment to extracellular matrix, and synthesis of some matrix proteins, particularly alpha 1 and alpha 2 chains of collagen IV.

Loss of heterozygosity on chromosome 1p in thyroid adenoma and medullary carcinoma, but not in papillary carcinoma

We analyzed 53 loci on 21 chromosomes other than chromosome 4 to detect possible loss of heterozygosity in 31 thyroid tumors using polymorphic DNA markers that detect allelic deletions at specific chromosomal loci. Loss of heterozygosity on chromosomes 1, 7 and 12 was detected in one follicular thyroid adenoma, and on chromosome 1 in two medullary thyroid carcinomas. However, no loss of heterozygosity was detected at any of the loci examined in papillary thyroid carcinomas. These results suggest that chromosomal loss detected in thyroid adenoma is one of the signals for risk of premalignant transformation, and that inactivation of unknown genes on chromosome 1p contributes to tumorigenesis of medullary thyroid carcinoma. Some genetic changes other than chromosomal losses may participate in the tumorigenesis of papillary thyroid carcinoma.

Transformation and amplification of the K-fgf proto-oncogene in NIH-3T3 cells, and induction of metastatic potential

A plasmid containing the K-fgf proto-oncogene linked to the dihydrofolate reductase gene has been constructed, and used in transfection experiments to investigate the effects of K-fgf expression on the tumorigenic and metastatic properties of NIH-3T3 fibroblasts. Analysis of cells transfected with K-fgf revealed that expression of the K-fgf proto-oncogene can, in a single step, induce both tumorigenic and metastatic characteristics, as determined in soft agar cloning experiments, and in tumorigenicity and experimental lung metastasis assays with BALB/c nu/nu mice. Selection for resistance to increasing concentrations of methotrexate lead to the isolation of a series of cell lines containing amplifications of both the dihydrofolate reductase gene and the linked K-fgf gene, which synthesized elevated levels of growth factor message and protein. The most highly resistant and gene amplified cell lines exhibited lower than expected levels of K-fgf mRNA, and also appeared to have down-regulated cell surface growth factor receptors. Further support for the concept that altered K-fgf expression can induce fully malignant and metastatic cells was obtained in experimental metastasis assays, where K-fgf transfected and gene amplified cell lines were highly aggressive.

Allelic 3p deletions in high-grade carcinomas after transformation in vitro of human uroepithelial cells

Restriction fragment length polymorphism (RFLP) analysis for allelic losses on the chromosome arm 3p were performed on independent carcinomas produced in athymic nude mice after transformation in vitro of a pseudodiploid clonal SV40-immortalized human uroepithelial cell line (SV-HUC). We analyzed ten primary carcinomas with heterogeneous phenotypes for deletions on 3p by using three informative probes, D3S30, D3S2, and D3F15S2, which map to the 3p11-p14, 3p21.1, and 3p21 regions, respectively. Five of the ten primary cancers showed reduction to homozygosity with at least one of the probes, and all five cancers were high-grade and poorly differentiated. We also analyzed six carcinomas that arose after progression of low-grade cancers, either spontaneously or after exposure to a human bladder carcinogen, to higher grades (progressed carcinomas). Four of the six exhibited 3p allelic loss. No preferential loss of a specific 3p allele was observed in any of the carcinomas. In addition, whereas most of the carcinomas showed allelic loss for all three of the probes, indicating a large-scale deletion, several of the carcinomas exhibited losses for only one or two of the probes, thus making it possible, along with the cytogenetic data, to define the least common region of deletion to 3p13----p14.2. These results support the hypothesis that nonrandom loss of a gene or genes on 3p leads to the development of cancer. Furthermore, these findings associate deletion of a putative 3p13----p14.2 tumor suppressor gene region with the development of high-grade uroepithelial carcinomas.

Assignment of the human prohibitin gene (PHB) to chromosome 17 and identification of a DNA polymorphism

Prohibition is a recently identified antiproliferative protein whose exact role in the cell is under investigation. To determine the human chromosomal location of the prohibition gene (PHB) and whether this site corresponds to that of any suspected tumor suppressor gene, we have analyzed DNA from three sources by hybridization analysis: mouse--human hybrid cell lines, hybrid cell lines containing portions of human chromosomes, and human metaphase chromosomes in situ. All three techniques confirm a location in the region 17q21-q22, a region genetically linked to early-onset human breast cancer. Further analysis will be required to establish the significance of this relationship; Southern hybridizations show a polymorphic EcoRI site that may be useful for this purpose.

The role of the matrix metalloproteinase stromelysin in the progression of squamous cell carcinomas

The expression of the metalloproteinase stromelysin correlates with the progression of chemically induced squamous cell carcinomas. We demonstrate that the expression of activated stromelysin in papilloma-derived cells enhances in vitro cell invasion. We also demonstrate that the Ha-ras oncogene induces the transcription of the stromelysin gene through an AP-1 dependent pathway. The hypothesis is that alterations in oncogenes and suppressor genes influence stromelysin expression and thus influence subsequent steps of tumor invasion and metastasis.

Cytogenetic findings in a pleomorphic xanthoastrocytoma

We report a pleomorphic xanthoastrocytoma with an abnormal clonal cell line of 48,XY, +3, +5, -20, -22, +der(7)t(7;?)(p22;?), +der(20)t(15;20)(q11;q13).

The SGP-2 gene is developmentally regulated in the mouse kidney and abnormally expressed in collecting duct cysts in polycystic kidney disease

Sulfated glycoprotein-2 (SGP-2) is a secreted, dimeric, glycosylated protein synthesized by a number of different epithelial cell types. Although its function is not yet understood, SGP-2 has been hypothesized to be involved in such diverse processes as the promotion of cell-cell interactions, spermatogenesis, modulation of the complement system, and programmed cell death. We have now found that the SGP-2 gene is developmentally regulated in the mouse kidney. SGP-2 gene expression is first detected in the condensing nephrogenic mesenchyme and is subsequently down-regulated during the maturation of the glomerular epithelia, proximal tubules, and collecting ducts. SGP-2 continues to be expressed in the mature kidney in distal tubules and in the urothelial lining of the calyx and papilla. We have also examined the expression of the SGP-2 gene in polycystic kidneys of the C57BL/6J-cpk mouse, a model of autosomal recessive polycystic kidney disease in which there is development of epithelial-lined cysts arising primarily from the collecting duct system. Abnormally high levels of SGP-2 mRNA were found in the cyst wall epithelium of polycystic kidneys. The expression of the SGP-2 gene in normal development suggests that it plays a role in differentiating epithelial structures; and the abnormally high levels of SGP-2 gene expression in polycystic kidneys suggests that the cells lining cysts are not fully differentiated. It is possible, therefore, that polycystic kidney disease is caused by a defective developmental process in which there is a delay in terminal differentiation.