Oncogenic point mutations in the human retinoblastoma gene: their application to genetic counseling

Inactivation of the retinoblastoma gene appears to be very uncommon in myelodysplastic syndromes

Rearrangements of the retinoblastoma (RB) gene have been reported in a few cases of myelodysplastic syndromes (MDS). In addition, low or absent expression of the RB protein is found in 20-30% of cases of acute myeloid leukaemias (AML), particularly in AML with a monocytic component (M4 or M5). We performed Southern blot analysis of the RB gene in 90 cases of MDS, including 37 cases of chronic myelomonocytic leukaemia (CMML). None of them had progressed to AML at the time of study. In 37/90 patients (including 20 CMML) Northern blot analysis, study of RB protein by immunocytochemistry on bone marrow slides, and detection of point mutations in exons 20-24 of the RB gene was also made, using single strand conformation polymorphism analysis (SSCP). No abnormal Southern profile was found in any of the 90 patients. Northern blot and immunocytochemical study of RB protein were normal in the 37 cases studied. SSCP analysis detected a point mutation in 2/37 patients tested. Direct sequencing confirmed the mutation in each case, which involved intron 21 and intron 23, respectively, and was located outside splicing sites of the neighbouring exons. These findings suggest that abnormalities of the RB gene and its expression must be very rare in MDS, and play a minor role, if any, in the pathophysiology of those disorders, at least before progression to AML.

Inactivation of oncoprotein binding by a single Cys706-to-Tyr substitution in the retinoblastoma protein

We previously found a new single amino acid substitution at codon 706 (Cys-to-Tyr) of the retinoblastoma (RB) gene in a sporadic retinoblastoma patient. The glutathione S-transferase-RB fused protein containing this mutation was here tested for binding to SV40 large T antigen and adenovirus E1A protein, and was shown to have lost its binding affinity. Thus, Tyr, as well as Phe, residues substituted for Cys706 were found to abolish the RB protein activity.

Differential immunohistochemical staining for retinoblastoma protein with the antibodies C15 and 1F8 in malignant mesothelioma

The results of an immunohistochemical study of retinoblastoma protein in human non-neoplastic mesothelium (40 cases) and in malignant mesothelioma (36 cases) using the antibodies 1F8 and C15 are reported. All cases of malignant mesothelioma and non-neoplastic mesothelium were immunoreactive in more than 75% of the mesothelial cells for retinoblastoma protein with the C15 polyclonal antibody. Immunoreactivity for retinoblastoma protein was virtually absent with the 1F8 monoclonal body in neoplastic cells of all investigated mesotheliomas. In contrast, stromal cells in these mesotheliomas and all cases with non-neoplastic mesothelium were immunoreactive with the monoclonal antibody 1F8 in more than 75% of the cells. These findings may be indicative for the presence of an abnormal retinoblastoma protein in malignant mesothelioma lacking an epitope coded for between exons 21-27.

Major patterns of human inheritance: relevance to the epilepsies

An understanding of the basic principles of human inheritance patterns is necessary to appreciate the variety and complexity of genetic influences in the epilepsies. The various modes of human inheritance include single gene (mendelian), chromosomal, mitochondrial, and multifactorial/polygenic. Recent insights regarding imprinting, anticipation, and uniparental disomy have been made and have an impact on our understanding of human genetics. All of these phenomena are likely to be of importance in the epilepsies and form the basis for a more detailed analysis of the relevant molecular biology.

Genetic analysis of p53 and RB1 tumor-suppressor genes in blast crisis of chronic myeloid leukemia

We have investigated the involvement of the p53 and RB1 tumor-suppressor genes in 26 cases of chronic myeloid leukemia (CML) blast crisis, including 17 myeloid, eight lymphoid, and one megakaryoblastic crisis. The presence of p53 mutations in exons 5 through 9 was tested by the PCR-single-strand conformation polymorphism (SSCP) assay, followed by PCR-direct sequencing; in addition, loss of heterozygosity (LOH) at 17p13, the site of the p53 gene, was assayed by Southern blot. Given the variability of the mechanisms of inactivation of the RB1 gene in human tumors, a combination of Southern blot and mutational analysis by PCR-SSCP was used. p53 mutations were restricted to one case of myeloid blast crisis, showing a CGC-->TGC (Arg-->Cys) mutation at codon 283; two additional cases displayed LOH at 17p13 in the absence of p53 mutations. No molecular lesions of the RB1 gene were detected in any of the cases analyzed. These data indicate that inactivation of p53 and RB1 is a rare event in the molecular pathogenesis of CML acute transformation.

A giant congenital orbital tumor: an unusual presentation of retinoblastoma

We report a case of an unusual giant congenital tumor presenting in a newborn infant as a large exophytic mass emerging from the left orbit. After enucleation orbital recurrence developed within 14 days. No anti-tumor treatment was given and the child died at the age of 4 weeks. The histopathological and cytogenetical analysis of the tumor is presented. The tumor was diagnosed as a retinoblastoma but we could not exclude the possibility of a neuroblastoma.

Mutations in the retinoblastoma gene and their expression in somatic and tumor cells of patients with hereditary retinoblastoma

Two intragenic deletions (exon 18-19 and exon 24) and two point mutations (one missense mutation in exon 21 and one mutation at splice-donor site for exon 13) were detected in the retinoblastoma gene in somatic and tumor cells of patients with hereditary retinoblastoma. Three mutations were located in a domain essential for binding to oncoproteins encoded by DNA tumor viruses (Hu et al., 1990; Huang et al., 1990). One mutation (deletion of exon 24) was outside this domain but it is in the region essential for binding to transcriptional factor E2F, and for suppression of malignant phenotypes (Qian et al., 1992; Qin et al., 1992). A minisatellite-like sequence and short repeated sequences were located at the breakpoint of the deletion of exon 24, suggesting that two deletions on both sides of the minisatellite-like sequence may be generated by a "DNA slippage and misalignment" mechanism. Upon amplification of cDNA by the polymerase chain reaction, no transcript of gene with frameshift mutation (deletion of exon 24) was detected in skin fibroblasts, while transcripts of genes with missense mutations were detected. The results, in combination with previous reports (Dunn et al., 1989; Hashimoto et al., 1991), suggest the instability of transcripts with a premature stop codon or the suppressed expression of alleles with a premature stop codon in the retinoblastoma gene in somatic cells of hereditary patients.

Infrequency of ras, p53, WT1, or RB gene alterations in Wilms tumors

BACKGROUND

Alteration of the ras family of oncogenes and of the tumor suppressor genes p53 and RB are the most common genetic events in human tumors. Although there have been no reports of the prevalence of these alterations in Wilms tumors, overexpression of the N-myc and insulin-like growth factor-II (IGF-II) genes have been observed, and alteration of another tumor suppressor gene (WT1) has been demonstrated.

METHODS

Forty-four Wilms tumor specimens were tested for the presence of N-, K-, and H-ras mutations in codons 12, 13, and 61 by single-strand conformation polymorphism (SSCP) analysis and direct DNA sequence analysis. Sixteen tumors were tested for abnormalities of WT1 by Southern and northern blot analysis and reverse transcriptase polymerase chain reaction (RT-PCR). N-myc, c-myc, WT1, and IGF-II mRNA expression was measured in 16 tumors by Northern blot analysis. Thirty-eight tumors were screened for p53 mutations by SSCP analysis and direct DNA sequence analysis. Nine tumors were analyzed for loss of heterozygosity (LOH) of RB.

RESULTS

Although the authors confirmed that N-myc and IGF-II are overexpressed in Wilms tumors, no mutations of ras family, p53, or RB genes were identified, and no gross alterations of WT1 were detected by Southern or Northern blot analysis.

CONCLUSIONS

These findings suggest that H-ras, K-ras, N-ras, p53, and RB are not involved in the pathogenesis of Wilms tumor.

Molecular genetics in neurology

There has been remarkable progress in the identification of mutations in genes that cause inherited neurological disorders. Abnormalities in the genes for Huntington disease, neurofibromatosis types 1 and 2, one form of familial amyotrophic lateral sclerosis, fragile X syndrome, myotonic dystrophy, Kennedy syndrome, Menkes disease, and several forms of retinitis pigmentosa have been elucidated. Rare disorders of neuronal migration such as Kallmann syndrome, Miller-Dieker syndrome, and Norrie disease have been shown to be due to specific gene defects. Several muscle disorders characterized by abnormal membrane excitability have been defined as mutations of the muscle sodium or chloride channels. These advances provide opportunity for accurate molecular diagnosis of at-risk individuals and are the harbinger of new approaches to therapy of these diseases.

Mechanisms of oncogenesis in patients with familial retinoblastoma

In an analysis of mutations in the RB1 gene in three patients, selected at random, who had a positive family history of tumours, we identified mutations, in constitutional cells, involving exons 3, 13 and 17 of the RB1 gene. We used SSCP and PCR sequencing to screen affected individuals and other members of their families. In two cases the mutations were 2 bp and 1 bp deletions identified in exons 3 and 17 respectively. The third mutation was a 1 bp insertion in exon 13. All three mutations lead to the generation of downstream premature stop codons as a result of frameshift changes, although the mutation in exon 3 possibly affects the splicing mechanism. The sites within the RB1 gene where these mutations occur contain interspersed repetitive DNA sequences, direct and inverted repeat sequences and/or dyad symmetrical elements suggesting that these areas promote the appropriate local sequence environment for the generation of deletions and insertions in the RB1 gene.

Molecular mechanisms of oncogenic mutations in tumors from patients with bilateral and unilateral retinoblastoma

The RB1 gene from 12 human retinoblastoma tumors has been analyzed exon-by-exon with the single-strand conformation polymorphism technique. Mutations were found in all tumors, and one-third of the tumors had independent mutations in both alleles neither of which were found in the germ line, confirming their true sporadic nature. In the remaining two-thirds of the tumors only one mutation was found, consistent with the loss-of-heterozygosity theory of tumorigenesis. Point mutations, the majority of which were C-->T transitions, were the most common abnormality and usually resulted in the conversion of an arginine codon to a stop codon. Small deletions were the second most common abnormality and most often created a downstream stop codon as the result of a reading frameshift. Deletions and point mutations also affected splice junctions. Direct repeats were present at the breakpoint junctions in the majority of deletions, supporting a slipped-mispairing mechanism. Point mutations generally produced DNA sequences which resulted in perfect homology with endogenous sequences which lay within 14 bp.

Oncogenes: present status

Oncogenes are genes associated with causation of cancer. They were originally associated with the ability of retroviruses to cause tumors in animals. These viral oncogenes (V-onc) have their cellular counterparts (C-onc) called Proto oncogenes. Function of Proto oncogenes is to maintain cellular growth and development. Activation of these proto-oncogenes can occur due to mutation which leads to uncontrolled cell growth. The Proto oncogenes can be grouped into different categories based on their protein products, i.e. protein kinases, growth factors, growth factor receptors, and DNA binding proteins. There are also genes that normally suppress malignant transformation and these are called anti oncogenes. Loss of their suppressor activity leads to unimpeded growth. Oncogene abnormalities are seen in pediatric leukemias, lymphomas, and various solid tumors. Anti oncogenes are associated with retinoblastoma (Rb gene), Wilms' tumor, rhabdomyosarcoma and neuroblastoma, etc. Identification of these abnormalities have diagnostic, prognostic and therapeutic implications. The utility of oncogenes in classification of human cancer and monitoring cancer therapy is quite clear, but the future of these for therapeutic interventions remains uncertain. Role of c-abl oncogene in chronic myeloid leukemia (CML), bcl-2, in lymphomas, N-myc in neuroblastomas and retinoblastoma (Rb) gene in retinoblastomas is well understood and used in designing proper therapeutic approaches. Since oncogenes also control normal cellular function, their use for therapy may be limited by the amount of damage to normal cells. Their maximum therapeutic benefit may be realized only when used in combination with other modalities.

Spectrum of spontaneous HPRT- mutations in TK6 human lymphoblasts

The occurrence of deletions, coding sequence alterations, and intronic changes leading to aberrant splicing has been characterized among 33 spontaneous HPRT- mutants in TK6 human lymphoblasts. Deletions detectable by multiplex PCR amplification accounted for 45% (15/33) of the mutant collection. Base substitutions represented 30% (10/33) of the total, and were predominated by changes at G:C base pairs. The remaining mutants were distributed among frameshifts (9%, 3/33), small deletions (6%, 2/33), and compound alterations (9%, 3/33). Five mutants (15%) demonstrated aberrant splicing of the hprt transcript. A cluster of 4 deletion/insertion events was identified in hprt exon 6. A nearly perfect 13 bp duplication differed from the original sequence only by an A:T to G:C transition, which was observed as a unique alteration in another HPRT- mutant. A model involving correction of a mismatch in a secondary structure formed by the duplicated sequence may account for these results.

Mutations of the APC (adenomatous polyposis coli) gene

Several investigators have reported germline mutations of the APC gene in patients with familial adenomatous polyposis (FAP) as well as somatic mutations in tumors developed in digestive organs (stomach, pancreas, colon, and rectum). Those results provide evidence that inactivation of the APC gene plays a significant role in FAP and in sporadic tumors of these tissues. APC mutations have led to some interesting observations. First, the great majority of the mutations found to date would result in truncation of the APC product. Second, almost all the mutations have occurred within the first half of the coding sequence, and somatic mutations in colorectal tumors are further clustered in a particular region called MCR (mutation cluster region). Third, most identified point mutations in the APC gene are transitions from cytosine to other nucleotides. Fourth, the location of germ-line mutations tends to correlate with the number of colorectal polyps in FAP patients. Furthermore, inactivation of both alleles of the APC gene seems to be required as an early event to develop most of adenomas and carcinomas in the colon and rectum as well as some of those in the stomach.

Tumour suppressor genes

Genes responsible for the hereditary predisposition to a variety of human cancers have now been isolated. Their function seems to be part of complex signalling pathways involved in the control of cellular differentiation and the cell cycle. The presence of a single copy of these genes appears to be sufficient to ensure normal development, i.e. prevents tumorigenesis, and has earned them the name--tumour suppressor genes.

Retinoblastoma: a hereditary tumor in children

Retinoblastoma, a malignant intraocular tumor of infancy and childhood, originates from primitive embryonal retinal cells. The cause of retinoblastoma is the loss or deletion of genetic information from the long arm of chromosome 13. Retinoblastoma has a hereditary form characterized by bilateral and multifocal tumors, and a nonheritable form that presents with a single tumor.

Genetics and cytogenetics of retinoblastoma

Retinoblastoma tumor formation is initiated by loss of function of both alleles at the RB1 locus on chromosome 13. In nonhereditary retinoblastoma (60% of patients), both mutations occur during retinal development. In hereditary retinoblastoma (40% of patients), tumor formation is caused by one germline and one somatic mutation. The RB1 gene encodes a nuclear protein that arrests progression through the G1 phase of the cell cycle. In the absence of intact RB1 protein, unscheduled cell proliferation occurs. Genes on chromosomes 1 and 6, which have not yet been identified, appear to be involved in later stages of tumorigenesis.

No alterations in exon 21 of the RB1 gene in sarcomas and carcinomas of the breast, colon, and lung

Studies of mutant genotypes of the retinoblastoma susceptibility gene (RB1) in different solid tumors have mainly been concentrated on the demonstration of loss of heterozygosity (LOH) at both internal and external polymorphic sites. One reason for this is the complex organization of the gene. The p105RB protein has been shown to interact with both DNA and regulatory cellular proteins and oncoproteins. The amino acids encoded by exon 21 are implicated in several of these interactions. Both point mutations and intragenic deletions involving exon 21 have previously been reported in human tumors. We have examined RB1 exon 21 from a number of human tumor types where significant LOH in or around the RB1 gene has been reported. DNA from 78 primary tumors was amplified using the polymerase chain reaction (PCR) with primers covering exon 21, followed by constant denaturant gel electrophoresis (CDGE). The 78 tumors included 11 breast carcinomas, 30 nonsmall cell lung carcinomas, 6 colon carcinomas, and 31 sarcomas. The small cell lung cancer cell line NCI-H209, previously shown to harbour a point mutation in codon 706: TGT- greater than TTT (Cys- greater than Phe), was detected using CDGE. Apart from this control mutant cell line, we did not detect any mutations in the examined region in any of the tumors.

Tumor suppressor genes

Tumor suppressor genes are negative regulators of cell growth. When their normal function is compromised, absence of their inhibitory effects can lead to unrestrained cell cycling and growth. Strong evidence now confirms that loss of proper function of these genes is a common occurrence leading to cancer. Their failure can be caused by alterations in the gene DNA or malfunction of their protein products. The recent extraordinary accumulation of knowledge about these genes reveals that normal carcinogenesis represents breakdown of normal regulatory processes.

Oncogenic point mutations in exon 20 of the RB1 gene in families showing incomplete penetrance and mild expression of the retinoblastoma phenotype

The retinoblastoma-predisposition gene, RB1, segregates as an autosomal dominant trait with high (90%) penetrance. Certain families, however, show an unusual low-penetrance phenotype with many individuals being unaffected, unilaterally affected, or with evidence of spontaneously regressed tumors. We have used single-strand conformation polymorphism analysis and PCR sequencing to study two such families. Mutations were found in exon 20 of RB1 in both cases. In one family a C----T transition in codon 661 converts an arginine (CGG) to a tryptophan (TGG) codon. In this family, incomplete penetrance and mild phenotypic expression were observed in virtually all patients, possibly indicating that single amino acid changes may modify protein structure/function such that tumorigenesis is not inevitable. In the second family the mutation in codon 675 is a G----T transversion that converts a glutamine (GAA) to a stop (TAA) codon. However, this mutation also occurs near a potential cryptic splice acceptor site, raising the possibility of alternative splicing resulting in a less severely disrupted protein.

Patterns of risk of hereditary retinoblastoma and applications to genetic counselling

A registry including information about nearly 1,600 cases of retinoblastoma diagnosed in Britain has been created at the Childhood Cancer Research Group. Cases have been classified as 'old germ cell mutation', 'new germ cell mutation' or 'sporadic non-hereditary'. For a population-based group of 918 cases diagnosed between 1962 and 1985 we have calculated the proportions of unilateral/bilateral and hereditary/non-hereditary cases. Bilateral cases represent 40% of the total number over this period; the proportion known to be hereditary is 44%, a higher proportion than has been reported elsewhere. By following up selected groups of cases, an estimate has been made of the proportions of siblings of retinoblastoma patients and offspring of survivors from retinoblastoma who are themselves affected with the disease. Where there is no previous family history, the risk for siblings of retinoblastoma patients of developing the disease is approximately 2% if the disease in the affected child is bilateral and 1% if it is unilateral, assuming that there are no other siblings; if there are unaffected siblings the risks for subsequent children are lower. Children of patients with hereditary retinoblastoma have a one in two chance of carrying the germ cell mutation and for those who are carriers the probability of developing retinoblastoma is very close to the accepted figure of 90% if the parents have bilateral retinoblastoma but probably less if they have the unilateral form. For children of patients not known to be carriers, the probability of developing retinoblastoma is estimated to be about 1%, considerably lower than the previously accepted figure of about 5%. Retinoblastoma kindreds consist mainly of bilateral cases but there is evidence that some kindreds have a high proportion of unilateral cases. The ways in which these findings may be used in conjunction with modern techniques of molecular biology for prenatal and postnatal genetic counselling are discussed.

Paternal selection favoring mutant alleles of the retinoblastoma susceptibility gene

Penetrance and segregation rates of mutant Rb-1 alleles were assessed in all 51 members of eight kindreds with hereditary retinoblastoma by concomitant ophthalmologic examination and determination of seven intragenic restriction fragment length polymorphisms (RFLPs). Penetrance was in the range reported in the literature except for one family in which it was only 42.8%. However, the odds of transmitting a mutant Rb-1 allele from one generation to the next were 25:9 in this population, much above the Mendelian 1:1 ratio (P less than 0.025). This preferential transmission was discovered through the use of molecular information. Further analysis revealed that this distortion was due to preferential inheritance among children of male carriers (18:4, P less than 0.005). No difference from a 1:1 segregation ratio could be detected among the children of female carriers (7:5). These findings were consistent with a review of relevant data in the literature.

Follow-up of retinoblastoma patients having prenatal and perinatal predictions for mutant gene carrier status using intragenic polymorphic probes from the RB1 gene

We have carried out presymptomatic prediction of mutant gene carrier status in ten individuals with a family history of retinoblastoma. In all cases standard linkage studies were employed using intragenic DNA probes which recognise restriction fragment length polymorphisms. In four cases foetal DNA samples were obtained by chorionic villus sampling, the remaining six were derived from either cord blood samples or venipuncture of neonates. We demonstrated that the mutant gene was inherited by only one of these patients who has subsequently developed bilateral tumours. Six of the other cases have now reached the age beyond which it might have been expected that tumours would develop and are all disease free. It must be concluded that repeated ophthalmological examination of these and future patients shown not to have inherited the mutant gene, is unnecessary.

Germ-line and somatic p53 gene mutations in multifocal osteogenic sarcoma

Multifocal osteogenic sarcoma patients without familial histories of increased tumor predisposition were examined for mutations in the highly conserved regions of the p53 gene. p53 point mutations were found in tumor DNA from each of the four patients we examined. A germ-line p53 mutation was detected in one of these patients, and a further rearrangement of the residual wild-type allele was detected in tumor tissue. p53 germ-line mutations can contribute to the enhanced predisposition to tumor development manifest in patients with multifocal osteosarcoma.

Germline mutations of the p53 tumor-suppressor gene in children and young adults with second malignant neoplasms

BACKGROUND

Acquired mutations in the p53 tumor-suppressor gene have been detected in several human cancers, including colon, breast, and lung cancer. Inherited mutations (transmitted through the germline) of this gene can underlie the Li-Fraumeni syndrome, a rare familial association of breast cancer in young women, childhood sarcomas, and other malignant neoplasms. We investigated the possibility that p53 mutations in the germline are associated with second primary cancers that arise in children and young adults who would not be considered as belonging to Li-Fraumeni families.

METHODS

Genomic DNA was extracted from the blood leukocytes of 59 children and young adults with a second primary cancer. The polymerase chain reaction, in combination with denaturant-gel electrophoresis and sequencing, was used to identify p53 gene mutations.

RESULTS

Mutations of p53 that changed the predicted amino acid sequence were identified in leukocyte DNA from 4 of the 59 patients (6.8 percent). In three cases, the mutations were identical to ones previously found in the p53 gene. The fourth mutation was the first germline mutation to be identified in exon 9, at codon 325. Analysis of leukocyte DNA from close relatives of three of the patients indicated that the mutations were inherited, but cancer had developed in only one parent at the start of the study.

CONCLUSIONS

These findings identify an important subgroup of young patients with cancer who carry germline mutations in the p53 tumor-suppressor gene but whose family histories are not indicative of the Li-Fraumeni syndrome. The early detection of such mutations would be useful not only in treating these patients, but also in identifying family members who may be at high risk for the development of tumors.

The retinoblastoma protein physically associates with the human cdc2 kinase

The protein product (pRB) of the retinoblastoma susceptibility gene functions as a negative regulator of cell proliferation, and its activity appears to be modulated by phosphorylation. Using a new panel of anti-human pRB monoclonal antibodies, we have investigated the biochemical properties of this protein. These antibodies have allowed us to detect a pRB-associated kinase that has been identified as the cell cycle-regulating kinase p34cdc2 or a closely related enzyme. Since this associated kinase phosphorylates pRB at most of the sites used in vivo, these results suggest that this kinase is one of the major regulators of pRB. The associated kinase activity follows the pattern of phosphorylation seen for pRB in vivo. The associated kinase activity is not seen in the G1 phase but appears in the S phase, and the levels continue to increase throughout the remainder of the cell cycle.

Detection of small RB1 gene deletions in retinoblastoma by multiplex PCR and high-resolution gel electrophoresis

Loss of function of both copies of the RB1 gene is a causal event in the development of retinoblastoma. The predisposition to this tumor can be inherited as an autosomal dominant trait. Direct detection of the genetic defect is important for presymptomatic DNA diagnosis and genetic counseling in families with hereditary retinoblastoma. We have used multiplex polymerase chain reaction and high-resolution polyacrylamide gel electrophoresis to detect RB1 gene deletions as small as one base pair. By using three independent sets of amplification reactions, which cover 26% of the RB1 gene coding region, we identified RB1 gene deletions in the DNA of peripheral blood cells in 3 out of 24 (12.5%) unrelated patients with hereditary retinoblastoma. In one case, formalin-fixed paraffin-embedded tumor material was also used to detect the mutation. Sequencing of the mutated alleles revealed deletions of 1, 3 and 10 base pairs. Each deleted region was flanked by direct repeats.

Cytogenetic and molecular investigation of a balanced Xq13q translocation in a patient with retinoblastoma

We report on a 4-year-old girl with retinoblastoma and de novo balanced translocation [46,X,t (X;13) (q23;q13)]. Unilateral retinoblastoma was discovered at age 9 months along with developmental delay and several manifestations of Turner syndrome. Chromosome studies showed an X/13 translocation and an X inactivation pattern showing the translocated X chromosome active in all 50 cells examined. Standard Southern blot analysis and pulsed field gel electrophoresis using a 3.8 kb EcoR1 fragment of the cDNA probe to the 3' end of the RB1 locus demonstrated a normal genomic pattern. The results of the cytogenetic and molecular analysis suggests that the RB1 locus has not been disrupted by the chromosome rearrangement. This case is the fifth report of an X/13 translocation associated with a retinoblastoma.

Selection of appropriate cellular and molecular biologic diagnostic tests in the evaluation of cancer

In this article, the use of cellular and molecular markers to diagnose and stage tumors is discussed. Their role in the evaluation of tumor prognosis and tumor susceptibility also is covered. The immunologic, cytogenetic, and molecular phenotype is discussed. Traditional markers are compared with newer methodologic approaches including evaluation of oncogenes, tumor suppressor genes, and genes that predict tumor susceptibility. These discussions are presented in relation to specific tumors. Finally, statements one might use to decide which tests to perform are presented.

The role of the retinoblastoma gene in tumour pathogenesis

Retinoblastoma is a rare tumour. The gene involved in the formation of retinoblastoma has been identified, and it has since been shown to be implicated in many other tumour types. In addition, patients with the familial form of retinoblastoma are known to be at an increased risk of developing second primary, non-ocular, malignancies. Retinoblastoma provides us with an important insight into the genetic mechanisms involved in tumorigenesis, to the extent that the retinoblastoma gene has now become the archetype of the 'tumour-suppressor' genes. The importance of this class of genes in tumorigenesis may come to exceed that of the oncogenes.

How do retinoblastoma tumours form?

The causes of retinoblastoma (RB) can now be described with considerable accuracy, although many details are still unclear. Understanding the genetic changes leading to RB has provided an awareness of general mechanisms of cancer development and progression, previously only suspected. From the basic understanding have come new diagnostic technologies that are now ready to be applied directly to RB patients and their families, and a rational approach, based on this understanding, will help us to develop new therapies that avoid the severe complications of conventional treatment.

The retinoblastoma protein physically associates with the human cdc2 kinase

The protein product (pRB) of the retinoblastoma susceptibility gene functions as a negative regulator of cell proliferation, and its activity appears to be modulated by phosphorylation. Using a new panel of anti-human pRB monoclonal antibodies, we have investigated the biochemical properties of this protein. These antibodies have allowed us to detect a pRB-associated kinase that has been identified as the cell cycle-regulating kinase p34cdc2 or a closely related enzyme. Since this associated kinase phosphorylates pRB at most of the sites used in vivo, these results suggest that this kinase is one of the major regulators of pRB. The associated kinase activity follows the pattern of phosphorylation seen for pRB in vivo. The associated kinase activity is not seen in the G1 phase but appears in the S phase, and the levels continue to increase throughout the remainder of the cell cycle.

Nuclear binding of purified retinoblastoma gene product is determined by cell cycle-regulated phosphorylation

The retinoblastoma tumor suppressor gene product (pRb) is a nuclear protein subject to cell cycle-regulated hyperphosphorylation. I constructed a recombinant vaccinia virus vector that expresses both the underphosphorylated and hyperphosphorylated forms of pRb and purified the recombinant protein by using immunoaffinity chromatography directed toward a synthetic carboxy-terminal epitope. To investigate the hypothesis that hyperphosphorylation of pRb is a means of controlling its growth-regulating activity, I tested purified pRb for the ability to be reincorporated into pRb-deficient nuclei in vitro. The underphosphorylated form of pRb efficiently reassociated with nuclei, but the hyperphosphorylated form remained soluble in this assay. Nuclear binding of pRb was enhanced by phosphatase treatment and reduced by phosphorylation of pRb effected by using a preparation of the cell cycle-regulatory kinase p34cdc2. Mutant-encoded proteins with altered E1A-binding domains failed to bind to nuclei. Pretreatment of target nuclei with nucleases and high-salt extraction did not alter the specificity of binding for underphosphorylated pRb. These observations demonstrate that hyperphosphorylation of pRb can regulate its interaction with nuclei, supporting the hypothesis that hyperphosphorylation controls the growth-regulatory activities of pRb. Further, at least one target of pRb binding appears to be an integral component of the nuclear envelope.

Nuclear binding of purified retinoblastoma gene product is determined by cell cycle-regulated phosphorylation

The retinoblastoma tumor suppressor gene product (pRb) is a nuclear protein subject to cell cycle-regulated hyperphosphorylation. I constructed a recombinant vaccinia virus vector that expresses both the underphosphorylated and hyperphosphorylated forms of pRb and purified the recombinant protein by using immunoaffinity chromatography directed toward a synthetic carboxy-terminal epitope. To investigate the hypothesis that hyperphosphorylation of pRb is a means of controlling its growth-regulating activity, I tested purified pRb for the ability to be reincorporated into pRb-deficient nuclei in vitro. The underphosphorylated form of pRb efficiently reassociated with nuclei, but the hyperphosphorylated form remained soluble in this assay. Nuclear binding of pRb was enhanced by phosphatase treatment and reduced by phosphorylation of pRb effected by using a preparation of the cell cycle-regulatory kinase p34cdc2. Mutant-encoded proteins with altered E1A-binding domains failed to bind to nuclei. Pretreatment of target nuclei with nucleases and high-salt extraction did not alter the specificity of binding for underphosphorylated pRb. These observations demonstrate that hyperphosphorylation of pRb can regulate its interaction with nuclei, supporting the hypothesis that hyperphosphorylation controls the growth-regulatory activities of pRb. Further, at least one target of pRb binding appears to be an integral component of the nuclear envelope.

Screening for germ-line mutations in familial adenomatous polyposis patients: 61 new patients and a summary of 150 unrelated patients

We report here the result of a screening for germ-line mutations in the adenomatous polyposis coli (APC) gene in 61 new familial adenomatous polyposis (FAP) patients as well as a summary of the results of 150 patients. Examination of the entire coding region of the APC gene, based on a ribonuclease protection assay coupled with the polymerase chain reaction (PCR), disclosed mutations that were considered to cause significant defects in the APC product in 97 of 150 unrelated FAP patients. Our findings revealed the following characteristics of the germ-line mutations of APC: 1) the great majority of the mutations were found to truncate the APC product; 2) almost all of the mutations were located within the first half of the coding region; 3) no correlation was observed between the locations of germ-line mutations and extracolonic manifestations in FAP patients; 4) more than 80% of base substitutions in the APC gene were from cytosine to other nucleotides, nearly one-third of which occurred at the GpG site. Our results provide information helpful to an understanding of the APC gene and will also contribute to presymptomatic diagnosis of members in FAP families.

The molecular biology of urological tumors

This article reviews the present understanding of chromosomal aberrations and specific genetic mutations in renal, bladder, and prostate cancers. In kidney tumors, specific emphasis is given to chromosome 3 deletions in renal cell carcinoma and the characterization of the WT1 gene in Wilms' tumor. In all three urological tumors, the presence of mutations in the RAS, P53, and RB genes (all of which often occur in other tumors) is analyzed. The expression and properties of the androgen receptor in prostate cancer are also summarized.

Gene mapping of ocular diseases

Increasing awareness of the role of genetic factors in the causation of many human eye diseases has made ocular genetics one of the fastest growing areas of ophthalmology. The objective of this paper is to present the basic principles of gene mapping and their application to ophthalmology. The techniques used to map the genome are reviewed with emphasis placed on molecular genetics. The advances in this area have already provided the major impetus to the areas of diagnosis and prevention of some genetic eye disorders. Tables are presented that list the autosomal, X-linked and mitochondrial assignment of eye genes and disorders with ocular involvement.

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.

DNA deaminating ability and genotoxicity of nitric oxide and its progenitors

Nitric oxide (NO), a multifaceted bioregulatory agent and an environmental pollutant, can also cause genomic alterations. In vitro, NO deaminated deoxynucleosides, deoxynucleotides, and intact DNA at physiological pH. That similar DNA damage can also occur in vivo was tested by treating Salmonella typhimurium strain TA1535 with three NO-releasing compounds, including nitroglycerin. All proved mutagenic. Observed DNA sequence changes were greater than 99% C----T transitions in the hisG46 (CCC) target codon, consistent with a cytosine-deamination mechanism. Because exposure to endogenously and exogenously produced NO is extensive, this mechanism may contribute to the incidence of deamination-related genetic disease and cancer.