Abnormalities of chromosome #13 in retinoblastomas from individuals with normal constitutional karyotypes

Personalized treatment approaches in intraocular cancer

Background

Intraocular malignant tumors represent a severe disease that threatens vision as well as life. To better extend the life of the patient, preserve visual function, and maintain ocular aesthetics, selecting the appropriate timing and methods of treatment becomes crucial.

Main text

With the continuous advancement of medical technology, the techniques and methods for treating intraocular malignant tumors are constantly evolving. While surgery was once considered the optimal method to prolong patient survival and prevent local recurrence, the discovery and application of various treatments such as radiotherapy, laser therapy, chemotherapy, cryotherapy, and monoclonal antibodies have led to a greater diversity of treatment options. This diversity offers more possibilities to develop personalized treatment plans, and thereby maximize patient benefit. This article reviews the various treatment methods for intraocular malignant tumors, including indications for treatment, outcomes, and potential complications.

Conclusions

Differentiating small intraocular malignant tumors from pigmented lesions is challenging, and ongoing monitoring with regular follow-up is required. Small to medium-sized tumors can be treated with radiotherapy combined with transpupillary thermotherapy. Depending on the tumor's distance from the optic disc, surgery with partial resection may be considered for distant tumors, while proximal tumors may require complete enucleation. Systemic chemotherapy has been widely applied to patients with retinal tumors, lymphomas, and intraocular metastatic cancers, but has limited efficacy in patients with choroidal melanoma. Antagonists of Vascular Endothelial Growth Factor (Anti-VEGF) drugs can improve patient vision and quality of life, while the efficacy of immunotherapy and molecular targeted therapy is still under research.

The regulatory landscape of retinoblastoma: a pathway analysis perspective

Retinoblastoma (Rb) is a rare intraocular tumour in early childhood, with an approximate incidence of 1 in 18 000 live births. Experimental studies for Rb are complex due to the challenges associated with obtaining a normal retina to contrast with diseased tissue. In this work, we reanalyse a dataset that contains normal retina samples. We identified the individual genes whose expression is different in Rb in contrast with normal tissue, determined the pathways whose global expression pattern is more distant from the global expression observed in normal tissue, and finally, we identified which transcription factors regulate the highest number of differentially expressed genes (DEGs) and proposed as transcriptional master regulators (TMRs). The enrichment of DEGs in the phototransduction and retrograde endocannabinoid signalling pathways could be associated with abnormal behaviour of the processes leading to cellular differentiation and cellular proliferation. On the other hand, the TMRs nuclear receptor subfamily 5 group A member 2 and hepatocyte nuclear factor 4 gamma are involved in hepatocyte differentiation. Therefore, the enrichment of aberrant expression in these transcription factors could suggest an abnormal retina development that could be involved in Rb origin and progression.

One hit, two hits, three hits, more? Genomic changes in the development of retinoblastoma

The childhood eye cancer retinoblastoma is initiated by the loss of both alleles of the prototypic tumor suppressor gene, RB1. However, a large number of cytogenetic and comparative genomic hybridization (CGH) studies have shown that these M1 and M2 mutational events--although necessary for initiation--are not the only genomic changes in retinoblastoma. Some of these subsequent changes, which we have termed M3 to Mn, are likely crucial for tumor progression not only in retinoblastoma but also in other cancers. Moreover, genes showing genomic change in cancer are more stable markers and, therefore, possible therapeutic targets than genes simply differentially expressed. In this review, we provide the first comprehensive summary of the genomic evidence implicating gain of 1q, 2p, 6p, and 13q, and loss of 16q in retinoblastoma oncogenesis, including karyotype, CGH, and microarray CGH data. We discuss the search for candidate oncogenes and tumor suppressor genes within these regions, including the candidates (KIF14, MDM4, MYCN, E2F3, DEK, CDH11, and others), plus associations between genomic changes and clinical parameters. We also review studies of other regions of the retinoblastoma genome, the epigenetic changes of aberrant methylation of MGMT, RASSF1A, CASP8, and MLH1, and the roles microRNAs might play in this cancer. Although many candidate genes have yet to be functionally validated in retinoblastoma, work in this field lays out a molecular cytogenetic pathway of retinoblastoma development. Candidate cancer genes carry diagnostic, prognostic, and therapeutic implications beyond retinoblastoma.

Molecular evidence for putative tumour suppressor genes on chromosome 13q specific to BRCA1 related ovarian and fallopian tube cancer

BACKGROUND/AIMS

Loss of heterozygosity (LOH) on chromosome 13q has been reported to occur frequently in human ovarian cancer, and indications have been found that chromosome 13 may also play a specific role in the inherited form of ovarian cancer. The aim of this study was to define regions on chromosome 13 that may harbour additional tumour suppressor genes involved in the tumorigenesis of BRCA1 related ovarian and fallopian tube cancer.

MATERIALS/METHODS

DNA extracted from paraffin wax blocks of 36 BRCA1 associated ovarian and fallopian tube carcinomas was analysed by LOH polymerase chain reaction using seven highly polymorphic microsatellite markers spanning chromosome 13q.

RESULTS

High LOH frequencies were found on loci 13q11, 13q14, 13q21, 13q22-31, 13q32, and 13q32-4, suggesting the presence of putative tumour suppressor genes on the long arm of chromosome 13 that may play a role in the pathogenesis of BRCA1 related ovarian and fallopian tube cancer. LOH patterns appeared to be independent of the type of BRCA1 mutation, stage, and grade. Although in some cases there were indications for loss of larger parts of chromosome 13, in most cases losses were fairly randomly distributed over chromosome 13 with retained parts in between lost parts. Microsatellite instability was found in six cases.

CONCLUSION

Several loci on chromosome 13q show high frequencies of LOH in BRCA1 related ovarian and fallopian tube cancer, and may therefore harbour putative tumour suppressor genes involved in the carcinogenesis of this particular type of hereditary cancer.

Cytogenetically unrelated clones in therapy-related myelodysplasia and acute myeloid leukemia: experience from the Copenhagen series updated to 180 consecutive cases

During the period from 1995 to 1997, we studied 19 new cases of therapy-related myelodysplasia (t-MDS) and acute myeloid leukemia (t-AML), extending our series to 180 consecutive cases: 123 patients with t-MDS and 57 patients with t-AML. Cytogenetically unrelated clones were observed in 13 patients: 11 patients with two unrelated clones, one patient with three unrelated clones, and one patient with four unrelated clones. Twelve cases of unrelated clones presented as t-MDS, whereas only one case presented as overt t-AML. Partial or complete deletions of the long arms or monosomy for chromosome 5 or chromosome 7, which are characteristic of t-MDS and t-AML, were observed in both unrelated clones in four patients and in one unrelated clone only in six patients, whereas three patients showed aberrations in both clones that were uncharacteristic of t-MDS or t-AML. Three different interpretations of the origin and significance of cytogenetically unrelated clones in t-MDS and t-AML are presented, although the disease is still considered to be monoclonal. First, patients with different defects of the long arm of chromosome 5 or chromosome 7 in two unrelated clones often seem to have acquired these aberrations as independent events. For this reason, it is possible that they may play an important role in leukemic transformation, for instance, by activating or potentiating the effect of a genetic change that is present in all cells but not disclosed as a visible chromosome abnormality. In cases with involvement of other chromosomes, unrelated clones sometimes develop by cytogenetic change in only a subclone of cells, indicating that they play a role only in tumor progression. Finally, unrelated clones in t-MDS and t-AML may represent two different monoclonal diseases: the primary tumor and t-MDS. This view is supported by the significant excess of unrelated clones observed in t-MDS following multiple myeloma (4 in 13 cases) compared with other diseases (9 in 167 cases; P = 0.02), and by results from a case with a balanced translocation that is highly characteristic of non-Hodgkin's lymphoma in one clone and a t-MDS-associated deletion of the long arm of chromosome 5 in another.

Genetic predisposition to cancer and familial cancer syndromes

Approximately 10% to 15% of childhood cancers are hereditary or familial in nature. For several genetic disorders, the development of cancer is a secondary manifestation of the clinical phenotype, whereas cancer predisposition syndromes are generally recognized by the manifestation of characteristic malignancies. The study of pediatric cancer and rare hereditary cancer syndromes and associations has led to the identification of numerous cancer genes that are known to play critical roles in both normal and abnormal cellular growth, differentiation, and proliferation. The potential to identify such genetic markers of cancer predisposition poses difficult social, legal, and ethical questions in their application to clinical practice.

The retinoblastoma gene and its significance

The first human tumour suppressor gene, the Retinoblastoma Susceptibility gene (RB1) was first demonstrated in retinoblastoma, a rare paediatric eye tumour which has been studied extensively over the last century. Genetic studies of retinoblastoma have yielded unique insights into familial cancer syndromes and the mechanisms of oncogenesis by tumour suppressor genes such as the RB1 gene. In this view, we will summarize past research into the genetics of retinoblastoma that led to the discovery of the RB1 gene and discuss the influence these results have had on the field of cancer research. In addition, we will discuss current research into RB1 as it relates to cancer and its potential for new therapies.

Lessons from our children

While the incidence of cancer is increasing among both children and adults, mortality rates have decreased for children, while they have increased for adults. Of children diagnosed with cancer today, 80% are predicted to be long-term survivors. Although there are differences between children and adults with respect to the tumor types, biology, and outcome, there are common lessons which we can learn from our children regarding the genetics of cancer, its management and treatment, and the importance of longitudinal studies of the survivors. Specific pediatric cancers, such as retinoblastoma, have led to the recognition of tumor suppressor genes, now also observed among adult tumors including sarcomas, breast, lung, and bladder cancer. The presence of the tumor suppressor gene provides an understanding for the incidence of second malignant tumors among patients with heritable diseases. Furthermore, cancer prone families, such as those with the Li-Fraumeni syndrome, also carry the p 53 tumor suppressor gene; the presence of which greatly increases the risk of developing invasive cancer. Childhood cancer is rare; it represents only 1% of the total US cancer problem. However, 53% of all children with cancer, but only 2% of all adults, are studied via the NCI cooperative group mechanism. For some specific childhood tumors such as rhabdomyosarcoma and Wilms' tumor, as many as 70-85% of all cases are managed via NCI sponsored trials. Essentially all pediatric cancer is treated by interdigitating radiation with surgical resection and systemic chemotherapy. This approach has contributed to high cure rates. Finally, our understanding of the late effects of being a cancer survivor have come from longitudinal studies of children. The most severe long-term effects related to radiation in childhood pertain to growth and development, infertility, and second malignant tumor induction. Here the children treated for Hodgkin's disease have taught us the dose and volume effects on axial skeletal and soft tissue growth. Infertility issues are also treatment-related and may often be obviated by using gonadal shielding. The risk of secondary leukemia is related to dose and class of specific chemotherapeutic agents administered; it is 5.5% among children receiving 6 cycles of MOPP. There is a 22-fold risk at 30 years of age of solid tumor induction following radiotherapy for children with Hodgkin's disease. These serious concerns have been offset by current therapeutic approaches of using lower doses and smaller volumes of radiation with fewer cycles of less toxic chemotherapeutic agents. Childhood cancer ranks high among number of person-years of potential life saved annually.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular characterization of the retinoblastoma susceptibility gene

Retinoblastoma is recognized as a hereditary cancer. Genetic and epidemiological analysis of the disease has been incorporated into a two-hit mutational inactivation hypothesis of the origin of retinoblastoma. The molecular cloning and characterization of the retinoblastoma gene and gene product has allowed a critical testing of this two-hit hypothesis. All the predications of the model have been born out by experiment so far. These include inheritance of one mutated RB allele as the origin of hereditary retinoblastoma, subsequent loss of the remaining allele upon tumorigenesis, the involvement of the same RB gene in both sporadic and hereditary retinoblastoma, the somatic mutation of both RB alleles in sporadic retinoblastoma, the lack of RB expression in any retinoblastoma yet examined, and the recessiveness of mutated RB alleles. The RB gene exhibits functional properties consistent with its role as a suppressor of tumor formation. For example, re-expression of RB in tumor cells lacking endogenous RB leads to a loss of tumorigenic properties. RB protein can also inhibit progression through the cell division cycle, and it physically and/or functionally interacts with important cell cycle regulatory molecules. Although confirmation of the two-hit hypothesis seems complete, we can not rule out the possibility that other genes are involved in the genesis of this tumor. For example, there seems to be variable resistance to tumor development even in patients inheriting retinoblastoma susceptibility. Further, heterozygous RB null mice do not develop retinoblastoma, but develop a characteristic brain tumor instead. The molecular isolation of the RB gene is an important achievement in research on cancer. For the first time, it has become possible to examine, at the molecular level, genes that inhibit the growth of tumor cells. The precise mechanism of action of RB is unknown, but a broad outline is beginning to emerge. RB seems to negatively influence tumor cell growth by participating in regulation of the cell division cycle. RB has also been implicated in differentiation; its effect on the cell division cycle and its effects on differentiation may be different manifestations of the same function. Since RB is involved in oncogenesis, gene regulation, and cellular differentiation, it is obviously an attractive gene for intense study; understanding the function and mechanism of action of RB will impact the understanding of many, important cell processes.

Small cell lung cancer: etiology, biology, clinical features, staging, and treatment

Lung cancer is the leading cause of cancer death in the United States. Small cell lung cancer (SCLC) accounts for 20% to 25% of all bronchogenic carcinoma and is associated with the poorest 5-year survival of all histologic types. SCLC differs in its etiologic, pathologic, biologic, and clinical features from non-SCLC, and these differences have translated to distinct approaches to its prevention and treatment. Compared with other histologic types of lung cancer, exposures to tobacco smoke, ionizing radiation, and chloromethyl ethers pose a substantially greater risk for development of SCLC. The histologic classification of SCLC has been revised to include three categories: (1) small cell carcinoma, (2) mixed small cell/large cell, and (3) combined small cell carcinoma. Ultrastructurally, SCLC displays a number of neuroendocrine features in common with pulmonary neuroendocrine cells, including dense core vesicles or neurosecretory granules. These dense core vesicles are associated with a variety of secretory products, cell surface antigens, and enzymes. The biology of SCLC is complex. The activation of a number of dominant proto-oncogenes and the inactivation of tumor suppressor genes in SCLC have been described. Dominant proto-oncogenes that have been found to be amplified or overexpressed in SCLC include the myc family, c-myb, c-kit, c-jun, and c-src. Altered expression of two tumor suppressor genes in SCLC, p53 and the retinoblastoma gene product, has been demonstrated. Cytogenetic and molecular evidence for chromosomal loss of 3p, 5q, 9p, 11p, 13q, and 17p in SCLC has intensified the search for other tumor suppressor genes with potential import in this malignancy. Bombesin/gastrin-releasing peptide, insulin-like growth factor I, and transferrin have been identified as autocrine growth factors in SCLC, with a number of other peptides under active investigation. Several mechanisms of drug resistance in SCLC have been described, including gene amplification, the recently described overexpression of multi-drug resistance-related protein (MRP), and the expression of P-glycoprotein. The classic SCLC staging system has been supplanted by a revised TNM staging system where limited disease and extensive disease are equivalent to the TNM stages I through III and stage IV, respectively. Therapeutically, recent strategies have attained small improvements in survival but significant reductions in the toxicities of chemotherapeutic regimens. Presently, the overall 5-year survival for SCLC is 5% to 10%, with limited disease associated with a significantly higher survival rate.(ABSTRACT TRUNCATED AT 400 WORDS)

Radiographic findings in 13q-syndrome

Of 169 children with retinoblastoma treated at our institution between 1962 and 1993, 5 had concurrent severe mental retardation, hypotonia, and abnormalities of constitutional chromosome 13. The associated skeletal abnormalities of these 5 children are described and include delayed skeletal maturation, metaphyseal abnormalities, microcrania, facial bone abnormalities, and gracile long bones.

Cytogenetics of epithelial malignant lesions

Chromosomal abnormalities have been believed to be responsible for neoplastic transformation and tumor growth for a long time. The confirming observations are of two types: (1) primary cytogenetic alterations that are responsible for tumor initiation and (2) secondary abnormalities that are acquired late and are associated with tumor growth, heterogeneity, and metastasis. Primary chromosomal abnormalities (such as the 13q deletion in retinoblastoma, 11p deletion in Wilms' tumor, 3p anomalies in renal cell carcinoma, and 5q deletion in colorectal carcinomas) first were identified in lymphocyte cultures as constitutional defects. Later, similar types of defects were observed as tumor-specific aberrations from patients whose lymphocytes otherwise had normal chromosomes. Recently, it has become clear that classes of known cancer-related genes (dominant protooncogenes and recessive tumor-suppressor or anti-oncogenes) are located at those hot spots that are involved in neoplasia-associated chromosomal alterations. In breast carcinoma, such a specific chromosomal alteration has not been identified conclusively in lymphocyte cultures, although chromosome 1 alterations have been observed in cell lines, directly processed effusions, and primary breast tumors. Lymphocyte cultures; primary tumors; and established cell lines from breast carcinomas, colorectal carcinomas, and renal cell carcinomas were analyzed to identify (1) primary chromosomal alterations precisely and (2) secondary cytogenetic defects that are associated with these most common solid adult neoplasms. Peripheral blood analysis indicated that chromosomes 1, 17, and 18 in breast carcinomas; chromosomes 3 and 14 in renal cell carcinomas; and chromosomes 5, 12, and 17 in colorectal carcinomas were involved nonrandomly in structural anomalies in a small number of lymphocyte cells (1-4%). These chromosomal aberrations were considered primary defects because of their involvement as marker formations in tumor cells; other structural and numeric abnormalities also were found. These results indicate that lymphocyte chromosomal analysis might identify those at high risk for breast, colorectal, and renal cell carcinomas, among other malignant lesions. Such identifications could facilitate early selection for primary and secondary cancer prevention or interventional trials.

Chromosome aberrations and cancer

Cancer may be defined as a progressive series of genetic events that occur in a single clone of cells because of alterations in a limited number of specific genes: the oncogenes and tumor suppressor genes. The association of consistent chromosome aberrations with particular types of cancer has led to the identification of some of these genes and the elucidation of their mechanisms of action. Consistent chromosome aberrations are observed not only in rare tumor types but also in the relatively common lung, colon, and breast cancers. Identification of additional mutated genes through other chromosomal abnormalities will lead to a more complete molecular description of oncogenesis.

Correlation between retinoblastoma gene expression and differentiation in human testicular tumors

Inactivation of the retinoblastoma gene (RB gene) is associated with the development of several human malignancies including retinoblastomas, some osteo- and soft tissue sarcomas, small cell lung cancer, and possibly breast and bladder cancers. To our knowledge, this gene has not been evaluated in human germ-cell malignancies. In this study 67 primary testicular germ-cell tumors and 4 testicular non-germ-cell malignancies were examined to determine the prevalence and nature of RB gene alterations. Decreased expression of RB gene mRNA was found in all testicular germ-cell tumors (both seminomas and nonseminomas) examined. The RB protein could not be detected by immunohistochemical analysis in the undifferentiated cells of any germ-cell tumors whereas the differentiated malignant cells present in 14/15 teratocarcinomas expressed the protein. No gross alterations of the RB gene were found at DNA level in any of the examined specimens. This and the presence of the RB protein in the more differentiated tumor cells of teratocarcinomas suggest that changes in transcript levels rather than mutation(s) of the gene may be responsible for the absent or decreased RB expression in human germ-cell tumors. To date studies on the mechanism of RB regulation have demonstrated that it occurs at the protein level by phosphorylation of the p105 gene product. The findings presented here indicate that additional regulation might occur at the transcript level.

Cytogenetic features of twenty-six primary breast cancers

Tumor preparations from 26 primary breast cancers were studied cytogenetically with G-banding, using a direct technique, synchronized short-term culture, or both. Two tumors had normal karyotypes, and 24 (92%) had chromosomal abnormalities. Nineteen tumors had chromosome 1 rearrangements, with 10 cases (40%) displaying distal short arm translocations (1p36). Other frequent breakpoints occurred at 3p21, 6q22-27, 11q21-25, 16q22-24, 17p, and 19q13. To seek primary rather than secondary cytogenetic changes, attention was directed toward tumors with diploid-range karyotypes (32-57 chromosomes per cell). Of four such tumors, three exhibited nonrandom involvement of chromosome 16q22. This, together with previously reported data, suggests that deletion or rearrangement of chromosome 16q21-24 may be a primary or specific event in a subset of breast cancers.

Fragile site induction by aphidicolin may be increased in parents of neuroblastoma patients

We recently demonstrated an increased expression of fragile sites, induced by aphidicolin, in lymphocytes of neuroblastoma patients. We have now extended our studies to parents of affected children with neuroblastoma to verify if this characteristic may be genetically transmitted. We have examined 20 families. In most of them, the hypersensitivity to aphidicolin was found in the affected child and in at least one parent. Moreover, some of the parents showed an increase in the expression of the fragile sites 1p32, 1p13, or both that are preferentially expressed in neuroblastoma patients. The possible relations between the hypersensitivity to aphidicolin and the inheritance of predisposition to neuroblastoma must be clarified.

Possible involvement of the retinoblastoma gene in undifferentiated sinonasal carcinoma

Retinoblastoma tumor formation is initiated by the loss of function of both alleles of the RB-1 gene on chromosome 13. Patients with the hereditary form of retinoblastoma carry a germ line mutation at one of the two homologous gene loci in all cells and have an increased risk for nonocular tumors (mainly osteosarcoma and other mesenchymal tumors) in later life. The authors studied a 38-year-old patient with sinonasal undifferentiated carcinoma (SNUC) who had been treated for bilateral retinoblastoma by enucleation (left eye) and irradiation (right eye), respectively. Using molecular probes for the RB-1 gene and other loci on chromosome 13, the authors detected a deletion at the RB-1 locus in metastatic SNUC cells that was not present in normal tissue. These findings indicate that somatic mutations at RB-1 locus may be involved in the formation or progression of ectodermal tumors.

Two distinct and frequently mutated regions of retinoblastoma protein are required for binding to SV40 T antigen

The retinoblastoma susceptibility gene (RB) encodes a phosphoprotein of 110 kd (pp110RB) that forms specific complexes with SV40 T antigen and the transforming proteins of several other DNA tumor viruses. Interaction with RB is thought to contribute to transformation by these viruses as demonstrated by genetic analyses. To help understand the function of these interactions, the regions of RB that are involved in binding to T have been mapped. An in vitro protein synthesis system capable of producing full-length RB protein has been developed to facilitate the mapping study. A 5- to 10-fold increase in translational efficiency in the reticulocyte lysate was obtained when the 5' non-coding region of RB mRNA was replaced with that of beta-globin mRNA or a plant viral RNA, alfalfa mosaic virus (AMV) RNA4. A series of mutated RB polypeptides produced from this system were assayed for T binding. Two non-contiguous regions of the RB protein, amino acid residues 394-571 and 649-773, were found to be necessary for binding to T: mutations in either region abolished T-RB complex formation. These results are consistent with the finding that, in all the cases analyzed so far, mutated RB proteins in human tumor cells also failed to bind to T antigen due to deletions including at least one of the two required regions. Thus the regions of RB defined in vitro as necessary for interaction with T might be physiologically relevant as well, and might play a fundamental role in normal RB protein function.

The regions of the retinoblastoma protein needed for binding to adenovirus E1A or SV40 large T antigen are common sites for mutations

The protein product of the retinoblastoma (RB) gene is thought to function in a pathway that restricts cell proliferation. Recently, transforming proteins from three different classes of DNA tumor viruses have been shown to form complexes with the RB protein. Genetic studies suggest that these interactions with the RB protein are important steps in transformation by these viruses. In order to understand better the function of the RB-viral oncoprotein complexes, we have mapped the regions of the RB protein that are necessary for these associations. Two non-contiguous regions of RB were found to be essential for complex formation with adenovirus E1A or SV40 large T antigen. These two regions are found between amino acids 393 and 572 and 646 and 772. Interestingly, these binding sites on RB overlap with the positions of naturally occurring, inactivating mutations of the RB gene. These results strongly suggest that these viral oncoproteins are targeting a protein domain that is an important site in the normal function of the RB protein.

Role of the retinoblastoma gene in the initiation and progression of human cancer

Images

Rhabdomyosarcoma-associated locus and MYOD1 are syntenic but separate loci on the short arm of human chromosome 11

The MYOD1 locus is preferentially expressed in skeletal muscle and at higher levels in its related neoplasm, rhabdomyosarcoma. We have combined physical mapping of the human locus with meiotic and physical mapping in the mouse, together with synteny homologies between the two species, to compare the physical relationship between MYOD1 and the genetically ascertained human rhabdomyosarcoma-associated locus. We have determined that the myogenic differentiation gene is tightly linked to the structural gene for the M (muscle) subunit of lactate dehydrogenase in band p15.4 on human chromosome 11 and close to the p and Ldh-1 loci in the homologous region of mouse chromosome 7. Because the rhabdomyosarcoma locus maps to 11p15.5, MYOD1 is very unlikely to be the primary site of alteration in these tumors. Further, these analyses identify two syntenic clusters of muscle-associated genes on the short arm of human chromosome 11, one in the region of rhabdomyosarcoma locus that includes IGF2 and TH and the second the tightly linked MYOD1 and LDHA loci, which have been evolutionarily conserved in homologous regions of both the mouse and the rat genomes.

Human retinoblastoma susceptibility gene

It is clear that the RB-deficient tumor cells lost their tumorigenicity in nude mice after regaining the RB gene expression. However, the mechanism of tumor suppression by the RB gene is still unknown. More studies on the biological activities of RB protein, pp110RB, are necessary to answer this question. Recent studies have shown that several oncogenic viral proteins, such as SV40 large T antigen (47) and adenoviral E1A protein (48), bind to RB protein. The significance of these bindings remains unclear; nevertheless, they suggest that depletion of functional RB protein by viral proteins may provide another mechanism of RB inactivation. Continued study of naturally occurring as well as engineered RB mutants may give us some information on the biological activity of RB protein, and its roles in oncogenesis, differentiation, development and gene regulation. Additionally, direct detection of RB gene mutations would have great clinical utility. Probes for the RB gene and gene product will be useful for genetic diagnosis of cancer susceptibility in affected families. Therefore, antibodies to the RB protein will be excellent tools for diagnostic and/or prognostic application in clinical medicine.

A model for embryonal rhabdomyosarcoma tumorigenesis that involves genome imprinting

Embryonal rhabdomyosarcomas (malignant pediatric tumors of striated muscle origin) have been shown to arise from cells that are clonally isodisomic for loci on chromosome 11p. We determined the parental origin of alleles in this genomic region in familial and sporadic cases of this disease and found that isodisomic chromosome 11p alleles in each tumor were of paternal origin. We have developed a modification of Knudson's two-hit model from these data that is capable of explaining the preferential allele retention and of resolving the apparent contradiction between such specific and early events in several embryonal tumors and discrepancies in the inheritance of predisposition in some of these diseases.

Synchronization of cultured retinoblastoma cells for high-resolution chromosomes showing up to 1000 bands

A method that allows high-resolution cytogenetic analysis of retinoblastoma cells in primary culture and subpassages is described. This method is based on the addition of high concentrations of bromodeoxyuridine or thymidine to obtain chromosomes subsequently banded to show 600-1000 bands. The results are compared with the standard harvest after 24 hours or long-term culture, and with low-temperature synchronization after long-term culture. After blocking with bromodeoxyuridine or thymidine, the chromosomes are significantly longer than after cold synchronization or after the unsynchronized techniques. When they are GTG, RHG, or GBG banded, more than 40% of the mitoses are in the earlier phases with chromosomes showing more than 600 bands per haploid set. This method significantly improves the general quality of retinoblastoma tumor cell chromosomes and increases diagnostic and prognostic accuracy.

An update on the cellular and molecular biology of brain tumors

Patients with tumors of the central nervous system (CNS) remain difficult to treat despite recent advances in surgical, chemotherapeutic and radiotherapeutic techniques. A better understanding of the molecular and cellular biology of neoplasia is providing neuroscientists with a framework on which to devise novel therapies for these patients. It thus becomes imperative that neurologists and neurosurgeons be aware of these advances in basic science that may eventually have a positive impact on patient management. This paper reviews our present knowledge of the process of CNS oncogenesis and the roles that chemicals, viruses, oncogenes, growth inhibitor genes, and growth factors play in the process.

Mechanism of i(6p) formation in retinoblastoma tumor cells

Isochromosome (6p) represents a highly characteristic cytogenetic abnormality of human retinoblastoma (RB) cells and may be important for tumor progression. To elucidate the mechanism by which this abnormal chromosome is formed, 24 RB tumors and three cell lines were studied by means of DNA polymorphisms specific for the short arm and the long arm of chromosome 6. Our results indicate that mitotic nondisjunction leading to trisomy 6 precedes the isochromosome formation. The isochromosome may then be formed by transverse division of the centromere or intrachromosomal chromatid exchange.

Studies on the human retinoblastoma susceptibility gene

The retinoblastoma susceptibility (RB) gene is unique among other cloned cancer genes because its causal role in a human cancer, retinoblastoma, was established by classical genetic methods before its isolation. Earlier hypotheses and experimental data suggested that inactivation of a gene in chromosome band 13q14 resulted in retinoblastoma formation. A gene in this region was identified as the RB gene on the basis of mutations found specifically in retinoblastoma tumors; however, its proposed biological activity in suppressing neoplasia has yet to be demonstrated. The RB gene product was identified as a nuclear phosphoprotein of 110 kD associated with DNA binding activity, suggesting that the RB protein may regulate other genes. Probes for the RB gene and gene product will be useful for genetic diagnosis of retinoblastoma susceptibility in affected families; for direct detection of mutant RB alleles; and, potentially, for genetic diagnosis of susceptibility to osteosarcoma and other tumors tentatively linked to RB-gene dysfunction. Continued study of the RB gene should yield further insight into mechanisms of oncogenesis, development, and gene regulation.

The gene responsible for the development of retinoblastoma and osteosarcoma

The gene responsible for the formation of both retinoblastoma and osteosarcoma recently has been isolated. This represents the first human recessive cancer gene ever cloned. Structural deletions within one or both retinoblastoma gene alleles were commonly noted in the retinoblastomas and an osteosarcoma. Whether or not changes were observed at the DNA level there was either no expression or an abnormal expression of the gene in the tumor. The fact that we could detect changes in the fibroblasts of some patients with the hereditary form of retinoblastoma also indicates that the gene can be used for diagnostic purposes.

Deletion (13)(q14.1q14.3) in two generations: variability of ocular manifestations and definition of the phenotype

A 5-yr-old girl with unilateral retinoblastoma was found to have del(13)(q14.1q14.3). Her 16-month-old sister and 35-year-old mother, with retinal colobomata but without retinoblastoma, have the same deletion. Esterase D studies indicate reduced gene dose at this locus in the 3 females, consistent with a deletion of band 13q14. These patients are of apparently normal intelligence but have a mildly "coarse" facial appearance, a broad nasal bridge, upturned nares, and a long upper lip with thin upper lip vermillion similar to the phenotype suggested by Motegi et al [1983a] for patients with this deletion. Review of the literature documents 2 other patients with deletions of band 13q14 but without retinoblastoma, indicating that retinoblastoma is not a necessary consequence of this deletion. Of the 12 reported patients with deletions limited to band 13q14, seven had normal intelligence and five were macrocephalic. Insufficient clinical information is provided to draw conclusions about phenotype. The family which we describe and those reviewed by Motegi et al suggest that there may be a characteristic appearance in patients with this deletion.

Molecular genetic approaches to the analysis of human ophthalmic disease

In this review of the recent literature, the contribution that the new techniques of molecular genetics has made in the analysis and diagnosis of human ophthalmic conditions is presented and discussed. Among the disorders reviewed are X-linked retinitis pigmentosa, Norrie's disease, gyrate atrophy and retinoblastoma, and there are also sections on crystallins and visual pigments.

Structural evidence for the authenticity of the human retinoblastoma gene

The retinoblastoma (Rb) gene is the prototype for a class of recessive human cancer genes in which loss of activity of both normal alleles is thought to be associated with tumorigenesis. Sixteen of 40 retinoblastomas examined with a complementary DNA probe shown to be the Rb gene had identifiable structural changes of the Rb gene including in some cases homozygous internal deletions with corresponding truncated transcripts. An osteosarcoma also had a homozygous internal deletion with a truncated transcript. In addition, possible hot spots for deletion were identified within the Rb genomic locus. Among those tumors with no identifiable structural changes there was either absence of an Rb transcript or abnormal expression of the Rb transcript. Comparison of the structural changes in the tumor cells and fibroblasts of certain patients provided support for Knudson's two-hit hypothesis for the development of retinoblastoma at the molecular level. The ability to detect germline structural deletions in fibroblasts from some patients with bilateral retinoblastoma also indicates that the isolated gene is useful for diagnostic purposes.

Cytogenetics of Mendelian mutations associated with cancer proneness

About 5% of Mendelian mutations displaying neoplastic tendencies are associated with chromosomal aberrations. The best established examples are retinoblastoma and del(13)(q14) and aniridia-Wilms' tumor and del(11)(p13). Evidence suggests that both mutations behave as dominant traits in the individual and as recessive traits in the cells. DNA analysis indicates that tumorigenesis arises from homozygosisty for the mutant allele at these loci, as a consequence of mitotic nondisjunction or from a mitotic recombination event. An additional argument for this conclusion is provided by the demonstration of duplication of 11p15 in some patients with the Beckwith-Wiedemann syndrome, which is complicated often by Wilms' tumor and other embryonal tumors. Data obtained with molecular probes have shown that also rhabdomyosarcoma and hepatoblastoma arise by homozygosity for a mutant allele at a locus on 11p, suggesting ontogenic relatedness of these tumor types. Additional examples of Mendelian mutations associated with chromosome deletions and neoplasia include Langer-Giedion syndrome with multiple exostoses and del(8)(q24.1), multiple endocrine neoplasia and del(20)(p12.2). While the presence of specific chromosome changes in subjects with high susceptibility to neoplasia does pinpoint the location of DNA sequences involved in the predisposition to certain types of cancers, selected Mendelian mutations associated with chromosome instability and cancer proneness may elucidate biological principles of cell proliferation and transformation. However, our current knowledge of mechanisms resulting in increased frequency of chromosome breakage and cancer susceptibility in ataxia-teleangiectasia, Fanconi's anemia, Bloom's syndrome, and similar conditions are still very incomplete.

Loss of heterozygosity in human ductal breast tumors indicates a recessive mutation on chromosome 13

The genotypes at chromosomal loci defined by recombinant DNA probes revealing restriction fragment length polymorphisms were determined in constitutional and tumor tissue from 10 cases of ductal breast cancer: eight premenopausal females and two males. Somatic loss of constitutional heterozygosity was observed at loci on chromosome 13 in primary tumor tissue from three females and one male. In two cases, specific loss of heterozygosity at three distinct genetic loci along the length of the chromosome was observed. In another case, concurrent loss of alleles at loci on chromosomes 2, 13, 14, and 20 was detected, whereas a fourth case showed loss of heterozygosity for chromosomes 5 and 13. In each instance, the data were consistent with loss of one of the homologous chromosomes by mitotic nondisjunction. Analysis of loci on several other chromosomes showed retention of constitutional heterozygosity suggesting the relative specificity of the events. In contrast, similar analyses of other breast cancers, including comedocarcinoma, medullary carcinoma, and juvenile secretory carcinoma, showed no loss of alleles at loci on chromosome 13. These data indicate that the pathogenesis of ductal breast cancer may, in a substantial proportion of cases, involve unmasking of a recessive locus on chromosome 13 and suggest the involvement of such a locus in heritable forms of this disease.

Human retinoblastoma susceptibility gene: cloning, identification, and sequence

Recent evidence indicates the existence of a genetic locus in chromosome region 13q14 that confers susceptibility to retinoblastoma, a cancer of the eye in children. A gene encoding a messenger RNA (mRNA) of 4.6 kilobases (kb), located in the proximity of esterase D, was identified as the retinoblastoma susceptibility (RB) gene on the basis of chromosomal location, homozygous deletion, and tumor-specific alterations in expression. Transcription of this gene was abnormal in six of six retinoblastomas examined: in two tumors, RB mRNA was not detectable, while four others expressed variable quantities of RB mRNA with decreased molecular size of about 4.0 kb. In contrast, full-length RB mRNA was present in human fetal retina and placenta, and in other tumors such as neuroblastoma and medulloblastoma. DNA from retinoblastoma cells had a homozygous gene deletion in one case and hemizygous deletion in another case, while the remainder were not grossly different from normal human control DNA. The gene contains at least 12 exons distributed in a region of over 100 kb. Sequence analysis of complementary DNA clones yielded a single long open reading frame that could encode a hypothetical protein of 816 amino acids. A computer-assisted search of a protein sequence database revealed no closely related proteins. Features of the predicted amino acid sequence include potential metal-binding domains similar to those found in nucleic acid-binding proteins. These results provide a framework for further study of recessive genetic mechanisms in human cancers.

Retinoblastoma, chromosome abnormalities and oncogene expression

Recurrent chromosomal abnormalities in retinoblastomas involve numbers 13, 1, and 6, as well as homogeneously staining regions (HSR) and double minutes (DMS). Evidence suggesting that chromosome 13 contains a gene responsible for tumorigenesis has already been presented. We postulate that the genetic changes resulting from abnormalities of chromosomes 1 and 6 and the HSR/DMS provide a selective growth advantage to cells in which they occur. Support for this hypothesis, as it relates to the HSR/DMS and oncogene amplification, is discussed.