Isolation of the murine Nbr1 gene adjacent to the murine Brca1 gene

The human NBR1 cDNA has previously been identified using polyclonal sera to CA125, an ovarian tumor antigen used in monitoring ovarian cancer. The gene was mapped to the BRCA1 region on chromosome 17q21 and subsequently found to lie in close proximity to the recently identified BRCA1 gene. The NBR1 protein has a B-box motif but the function of the protein is as yet unknown. To investigate the function and importance of this gene, we have studied the conservation of this gene in other species and in particular in the mouse. We have isolated murine Nbr1 cDNA and genomic clones. Translation of the cDNA sequence indicates that the protein is highly conserved, being 89% similar and 84% identical to the human. Analysis of the murine Nbr1 genomic clones indicates that it maps less than 1 kb from the Brca1 gene and that, unlike that in human, this region is not duplicated.

Spinal bupivacaine in ambulatory surgery: the effect of saline dilution

The safety of lidocaine spinal anesthesia has recently been called into question by reports of both permanent and transient neurologic toxicity. This study explored the possibility of adapting the longer acting spinal bupivacaine to ambulatory surgery. Sixty patients presenting for ambulatory arthroscopy were randomized to four groups receiving the following spinal anesthetics: Group I (15 mg bupivacaine), 3 mL of 0.5% spinal bupivacaine in 8% dextrose; Group II (10 mg bupivacaine), 2 mL of the 0.5% spinal bupivacaine+1 mL saline; Group III (7.5 mg bupivacaine), 1.5 mL of the 0.5% spinal bupivacaine%1.5 mL saline; Group IV (5 mg bupivacaine), 1 mL of the 0.5% spinal bupivacaine+2 mL saline. Maximum block height was T-5 in Group I versus T-8 in the other groups. Onset times to peak block were similar in all groups and averaged 14 min. Time to two-segment regression, complete regression, micturition, and discharge were significantly reduced from Group I to Group II and from Group II to Group III. Reductions in times between Groups III and IV did not achieve statistical significance. Times from placement of the spinal block until discharge were 471 +/- 35, 260 +/- 15,202 +/- 14, and 181 +/- 8 min, respectively, for the four groups. The intensity of motor block decreased significantly from group to group, such that 13 of the 15 patients in Group IV failed to achieve Bromage level 2 or 3. The intensity of sensory block also decreased from group to group with four patients in Group IV having pain intraoperatively that required further treatment. Therefore, Group III provided the optimum combination of adequate depth of anesthesia and rapid recovery. The results of this study indicate that spinal anesthesia with 7.5 mg of 0.5% bupivacaine in 8% dextrose diluted with an equal volume of saline provides an acceptable spinal anesthetic for ambulatory arthroscopy with a recovery profile appropriate to the ambulatory setting.

PIC 1, a novel ubiquitin-like protein which interacts with the PML component of a multiprotein complex that is disrupted in acute promyelocytic leukaemia

Acute promyelocytic leukaemia (APL) arises following a reciprocal translocation t(15;17) that fuses PML with retinoic acid receptor alpha (RARA). The PML-RARA fusion protein targets and disrupts nuclear multiprotein complexes called PODs, ND10 or NBs, a process which is associated with a block in myeloid differentiation leading to APL. A human B-cell cDNA library was screened for PML-interacting clones and a single positive clone (PIC1) was isolated. The sequence of PIC1 shows 52% identity to a S. cerevisiae ubiquitin-like protein that was cloned as a suppressor of mutations in MIF2, a protein required for mitotic spindle integrity during anaphase. Transient transfection of NIH3T3 cells with PIC1 results in a nuclear staining pattern coincident with that of endogenous mouse PML. Further, cotransfection of PIC1 with human PML produces a completely overlapping staining pattern between the two proteins. An antibody raised against PIC1 detects a punctate staining pattern in HeLa cells that is coincident with endogenous human PML. There is no significant colocalisation observed between the staining of PML/ PML-RARA and PIC1 in an APL-derived cell line NB4, as compared to cells expressing only wild type PML. However, following all trans retinoic acid treatment of NB4 cells a significant relocalisation of PIC1 and PML is observed. PIC1 is the first identified NB-associated protein that interacts with PML, the function of which may lead to a fuller understanding of the molecular events leading to APL.

The frequency and mechanism of loss of heterozygosity on chromosome 11q in breast cancer

Loss of heterozygosity (LOH, allele loss) occurs frequently on the long arm of chromosome 11 in breast cancer. Seventy-one paired tumour/normal DNA samples from breast cancer patients under 50 years old were studied for allele loss at four microsatellite loci on 11q: D11S29 (11q23.3), NCAM (11q22-q23), D11S968 (11qtel), and D11S1313 (11qcen). The maximum frequency of LOH (approximately 35 per cent) was found at the D11S29 and NCAM loci. This result is consistent with previous studies and the frequency of allele loss is moderate to high compared with the usual baseline of 0-20 per cent. In most of the cases studied, LOH on chromosome 11q could be accounted for by one of two mechanisms. Either chromosomal non-disjunction had occurred, or sequences stretching from the telomere at least as far as NCAM had undergone deletion or mitotic recombination. These results suggest that a putative tumour suppressor gene is most likely to exist near 11q22-q23. There was a very low frequency of microsatellite instability in the tumours. An association was found between lack of progesterone receptor (PgR) expression and LOH at NCAM, suggesting that deletion of sequences on 11q may prevent high levels of PgR expression in some cases.

Establishing the presence of the t(15;17) in suspected acute promyelocytic leukaemia: cytogenetic, molecular and PML immunofluorescence assessment of patients entered into the M.R.C. ATRA trial. M.R.C. Adult Leukaemia Working Party

Detection of the t(15;17) or its molecular consequence, the PML-RAR alpha rearrangement, is critical for meaningful analysis of clinical trials involving patients with suspected acute promyelocytic leukaemia (APL). Its presence remains the best predictor of a favourable response to retinoids, such as ATRA, which in combination with chemotherapy confer significant improvements in disease-free survival. We have evaluated the relative efficacy of RT-PCR, cytogenetics and PML immunofluorescence staining to identify the existence of the translocation in 100 patients entered into the Medical Research Council (M.R.C.) ATRA trial. RT-PCR successfully identified PML-RAR alpha rearrangements in 93/100 patients, including 65 where only peripheral blood or post-induction marrow samples were available for analysis and in 12 patients in whom cytogenetic assessment failed to demonstrate t(15;17) due to poor-quality metaphases (10/12) or as a reflection of cryptic PML-RAR alpha rearrangements (2/12). Parallel employment of the RAR alpha-PML assay confirmed expression of del(17q)-derived transcripts in 81% and permitted determination of the PML breakpoint (a potential independent prognostic variable) in all 93 cases. Sequencing of RT-PCR products derived from 50 patients with 3' PML breakpoints revealed five bcr 2 cases, including a novel exon 5 breakpoint. 35/81 (43%) patients with cytogenetic evidence of t(15;17) possessed additional karyotypic abnormalities. In four patients with available buffy coat smears, lack of cytogenetic or molecular evidence of the t(15;17) was confirmed by a wild-type PML immunofluorescence nuclear staining pattern, in contrast to the characteristic microparticulate distribution detected in 14 patients with RT-PCR evidence of the rearrangement. However, although PML immunofluorescence staining is suitable for rapid determination of patients likely to benefit from ATRA, this approach does not obviate the need for cytogenetic and RT-PCR analysis of all patients entered into APL clinical trials, because both techniques provide additional information which may prove to be of independent prognostic significance.

The 5' end of the BRCA1 gene lies within a duplicated region of human chromosome 17q21

To begin to address the hypothesis that abnormal regulation of the breast/ovarian cancer susceptibility gene BRCA1 is a critical step in sporadic breast/ovarian tumorigenesis, we have determined the detailed structure of the BRCA1 genomic region. We show that this region of the genome contains a tandem duplication of approximately 30 kilobases, which results in two copies of BRCA1 exons 1 and 2, of exons 1 and 3 of the adjacent 1A1-3B gene and of the previously reported 295 base pair intergenic region. Sequence analysis of the duplicated exons of BRCA1 and 1A1-3B and flanking genomic DNA reveals maintenance of the intron-exon structure and a high degree of nucleotide sequence identity, suggesting that these are non-processed pseudogenes and that the duplication is a recent event in evolutionary terms. We also show that a processed pseudogene of the acidic ribosomal phosphoprotein P1 (ARPP1) is inserted directly upstream of pseudo-BRCA1 exon 1A. We believe that these findings could not only confound BRCA1 mutation analysis, but could have implications for the normal and abnormal regulation of BRCA1 transcription, translation and function.

Genetic mapping of hereditary mixed polyposis syndrome to chromosome 6q

Hereditary mixed polyposis syndrome (HMPS) is characterized by atypical juvenile polyps, colonic adenomas, and colorectal carcinomas. HMPS appears to be inherited in an autosomal dominant manner. Genetic linkage analysis has been performed on a large family with HMPS. Data did not support linkage to the APC locus or to any of the loci for hereditary nonpolyposis colorectal cancer. Evidence that the HMPS locus lies on chromosome 6q was, however, provided by significant two-point LOD scores for linkage between HMPS and the D6S283 locus. Analysis of recombinants and multipoint linkage analysis suggested that the HMPS locus lies in a 4-cM interval containing the D6S283 locus and flanked by markers D6S468 and D6S301.

In vivo and in vitro characterization of the B1 and B2 zinc-binding domains from the acute promyelocytic leukemia protooncoprotein PML

Acute promyelocytic leukemia (APL) has been ascribed to a chromosomal translocation event which results in a fusion protein comprising the PML protein and retinoic acid receptor alpha. PML is normally a component of a nuclear multiprotein complex which is disrupted in the APL disease state. Here, two newly defined cysteine/histidine-rich protein motifs called the B-box (B1 and B2) from PML have been characterized in terms of their effect on PML nuclear body formation, their dimerization, and their biophysical properties. We have shown that both peptides bind Zn2+, which induces changes in the peptides' structures. We demonstrate that mutants in both B1 and B2 do not form PML nuclear bodies in vivo and have a phenotype that is different from that observed in the APL disease state. Interestingly, these mutations do not affect the ability of wild-type PML to dimerize with mutant proteins in vitro, suggesting that the B1 and B2 domains are involved in an additional interaction central to PML nuclear body formation. This report in conjunction with our previous work demonstrates that the PML RING-Bl/B2 motif plays a fundamental role in formation of a large multiprotein complex, a function that may be common to those unrelated proteins which contain the motif.

Haplotype and phenotype analysis of six recurrent BRCA1 mutations in 61 families: results of an international study

Several BRCA1 mutations have now been found to occur in geographically diverse breast and ovarian cancer families. To investigate mutation origin and mutation-specific phenotypes due to BRCA1, we constructed a haplotype of nine polymorphic markers within or immediately flanking the BRCA1 locus in a set of 61 breast/ovarian cancer families selected for having one of six recurrent BRCA1 mutations. Tests of both mutations and family-specific differences in age at diagnosis were not significant. A comparison of the six mutations in the relative proportions of cases of breast and ovarian cancer was suggestive of an effect (P = .069), with 57% of women presumed affected because of the 1294 del 40 BRCA1 mutation having ovarian cancer, compared with 14% of affected women with the splice-site mutation in intron 5 of BRCA1. For the BRCA1 mutations studied here, the individual mutations are estimated to have arisen 9-170 generations ago. In general, a high degree of haplotype conservation across the region was observed, with haplotype differences most often due to mutations in the short-tandem-repeat markers, although some likely instances of recombination also were observed. For several of the instances, there was evidence for multiple, independent, BRCA1 mutational events.

Mutations of the BRCA1 gene in human cancer

BRCA1 is a putative tumour suppressor gene located on chromosome 17q21. It spans 100kb of genomic DNA and encodes a protein of 200kD consisting of 1863 amino acids. Sixty-three distinct germline mutations of BRCA1 have now been identified in more than 100 patients with breast and/or ovarian cancer. These mutations are distributed across the entire coding region of the BRCA1 gene, and the majority (87%) are predicted to result in truncated proteins or loss of a BRCA1 transcript. No somatic mutations of the BRCA1 gene have been identified in sporadic breast cancers, though five mutations have been found in sporadic ovarian tumours. This suggests that mutations in the BRCA1 gene may play a significant role in the tumorigenesis of familial breast cancer but not of sporadic breast cancer.

Ordering of 66 STSs along the entire short arm of human chromosome 17 and chromosome assignment of a transcribed sequence (FMR1L2) homologous to FMR1

Sixty-four PCR-markers previously assigned to the short arm of chromosome 17 and two newly established STSs were localized on a hybrid cell-YAC clone panel. The 66 STSs fell into 23 unique retention patterns, providing a map converting the entire short arm of human chromosome 17 with an average resolution of approximately 1.2 Mb. The combination of radiation-reduced hybrids, somatic cell hybrids and selected YAC clones enabled the precise localization of break-points in two cell hybrids. Since polymorphic STSs from the CEPH as well as the UTAH genetic map were used in this study, a physical link has been generated between these two high resolution genetic maps. FMR1L2, a second FMR1 autosomal homologue has been identified and assigned to a genomic interval between D17S796 and D17S799.

Minimal residual disease detection in acute promyelocytic leukemia by reverse-transcriptase PCR: evaluation of PML-RAR alpha and RAR alpha-PML assessment in patients who ultimately relapse

RT-PCR assays used to detect acute promyelocytic leukemia (APL) are generally considered less sensitive than those for other hematological malignancies, such as CGL. Most patients with APL express del(17q)-derived RAR alpha-PML transcripts as well as the putative leukemogenic PML-RAR alpha associated with add(15q). We have found that a nested RT-PCR for RAR alpha-PML affords greater sensitivity than that for PML-RAR alpha, particularly in patients with the commonest breakpoint pattern. Therefore, we have evaluated both assays in parallel to monitor a group of 12 de novo APL patients who relapsed despite treatment with both all-trans retinoic acid (ATRA) and chemotherapy. 5' (bcr 3) breakpoints in PML were over represented among the group and three patients had complex cytogenetic abnormalities suggesting both factors may increase the risk of relapse. The RAR alpha-PML assay changed the PCR status of two patients in morphological remission; in both cases disease contamination of bone marrow harvest specimens was detected. Although parallel assessment of PML-RAR alpha and RAR alpha-PML can enhance minimal residual disease detection in APL, this study demonstrates that treatment strategies involving determination of PCR status post-consolidation, even using RAR alpha-PML in addition to the more conventional PML-RAR alpha assay will fail to identify all patients at risk of relapse. Whether the duration of PCR positivity is a helpful prognostic indicator in those patients who ultimately become PCR negative is being addressed by

Localization of the human RNA polymerase I transcription factor gene (UBTF) to the D17S183 locus on chromosome 17q21 and construction of a long-range restriction map of the region

Human upstream binding factor (hUBF) is a sequence-specific DNA-binding protein that is essential for the activation of human 18s and 28s rRNA gene transcription. We have isolated and localized the gene (UBTF) encoding hUBF to the D17S183 locus on chromosome 17q21 by analyzing a cosmid from the region and carrying out Southern analysis on a previously constructed chromosome 17 somatic cell hybrid mapping panel using a probe from the hUBF cDNA. Confirmation of its location at this region was obtained from the results of pulsed-field gel electrophoresis analysis of genomic DNA using the hUBF cDNA and other probes from the region. These data also enabled the construction of a long-range restriction map of the region.

Distinct transcription start sites generate two forms of BRCA1 mRNA

Using primer extension and 5' RACE, we have mapped the 5' end of the BRCA1 gene and identified a new 5' exon. Two distinct BRCA1 transcripts differing by the first exons were found; these transcripts were generated by the alternative use of dual promoters and alternative splicing. The expression of the distinct transcripts was examined in four primary tissues (placenta, mammary gland, testis and thymus), six normal or cancer cell lines, four primary breast tumor tissues and four primary ovary tumour tissues. Both transcripts were detected in all the samples studied, with the exon 1a transcript being the major expressed form in mammary gland and the exon 1b transcript in placenta. This suggests that the two transcripts may be expressed in a tissue-specific fashion. The 5' flanking regions of both BRCA1 transcripts were analysed, neither contains a TATA box. Initiator elements, which have been proposed to mediate transcription in TATA-less promoters, were found at the transcription initiation sites. Transcription factor binding sites such as Sp1, PEA3, C/EBP, CREB, E4F1 and Pu boxes were identified in the 5' flanking regions of the exon 1a transcript, and Sp1, NF-kB and PEA3 binding sites in the 5' flanking region of the exon 1b transcript. The interactions of these DNA elements with trans-acting factors are likely to modulate the alternative use of the distinct transcription start sites and the expression of the BRCA1 gene.

Cloning of the murine homolog of the leukemia-associated PML gene

PML, a Ring-finger protein, participates in the disruption of normal myeloid differentiation when fused to the retinoic acid receptor alpha (RAR alpha) by the translocation between chromosomes (Chrs) 15 and 17 in acute promyelocytic leukemia (APL). As an initial step in the characterization of PML in species other than human, a murine cDNA clone of the PML gene was isolated and sequenced, and the intron/exon organization of the murine locus determined. The predicted amino acid sequence of the mouse PML protein shows 80% similarity to that of its human homolog. However, the mouse and human proteins show greater than 90% similarity in the proposed functional domains of the proteins. Despite its role in the etiology of APL, PML expression is not detectably altered during granulocytic differentiation in a murine in vitro system. Chromosomal localization of the Pml locus by somatic cell hybrids and by linkage analysis indicates that the gene maps to a region of mouse Chr 9 with known linkage homology to the region on human Chr 15q to which PML has been localized.

Physical mapping, cloning, and identification of genes within a 500-kb region containing BRCA1

BRCA1 is a breast/ovarian cancer susceptibility gene on human chromosome 17q21. We describe a complete and detailed physical map of a 500-kb region of genomic DNA containing the BRCA1 gene and the partial cloning in phage P1 artificial chromosomes. Approximately 70 exons were isolated from this region, 11 of which were components of the BRCA1 gene. Analysis of the other exons revealed a rho-related G protein and the interferon-induced leucine-zipper protein IFP-35.

The solution structure of the RING finger domain from the acute promyelocytic leukaemia proto-oncoprotein PML

Acute promyelocytic leukaemia (APL) has been ascribed to a chromosomal translocation event which results in a fusion protein comprising the PML protein and the retinoic acid receptor alpha. PML is normally a component of a nuclear multiprotein complex (termed ND10, Kr bodies, nuclear bodies, PML oncogenic domains or PODs) which is disrupted in the APL disease state. PML contains a number of characterized motifs including a Zn2+ binding domain called the RING or C3HC4 finger. Here we describe the solution structure of the PML RING finger as solved by 1H NMR methods at physiological pH with r.m.s. deviations for backbone atoms of 0.88 and 1.39 A for all atoms. Additional biophysical studies including CD and optical spectroscopy, show that the PML RING finger requires Zn2+ for autonomous folding and that cysteines are used in metal ligation. A comparison of the structure with the previously solved equine herpes virus IE110 RING finger, shows significant differences suggesting that the RING motif is structurally diverse. The role of the RING domain in PML nuclear body formation was tested in vivo, by using site-directed mutagenesis and immunofluorescence on transiently transfected NIH 3T3 cells. Independently mutating two pairs of cysteines in each of the Zn2+ binding sites prevents PML nuclear body formation, suggesting that a fully folded RING domain is necessary for this process. These results suggest that the PML RING domain is probably involved in protein-protein interactions, a feature which may be common to other RING finger domains.

The growth of postdoctoral general dentistry programs

From 1972 to 1990, the number of Postdoctoral General Dentistry (PGD) programs increased by 57% and enrollment increased by 57% and enrollment increased by 131% for a total of 118 PGD programs and 1,367 positions. Although there has been some increase in military and Veterans Affairs (VA) programs, the major increase was in civilian programs. From 1972-78, the major impetus for growth was hospital sponsorship of General Practice Residency (GPR) programs. With federal funding of PGD programs, civilian GPR programs continued to be the main source of growth until the accreditation of Advanced Education in General Dentistry (AEGD) programs in 1981. Subsequently, almost all increases were in AEGD programs. Over the 12-year period of federal funding (1978-90), there was an increase of 406 civilian PGD positions to make a total of 925 positions. The increase in enrollment directly attributable to federal funding was 242. The "unmet demand" for PGD programs was estimated to be approximately 300 positions for 1990, from data derived from the Survey of Dental Seniors and the Matching Program. Assuming that the number of PGD positions continues to increase by 35 positions a year, as it has in the past 12 years, the unmet demand would be met in slightly less than 10 years. If, however, a postdoctoral year was mandated for licensure, the increase in the number of positions would be far short of projected need.

Towards cloning the familial breast-ovarian cancer gene on chromosome 17

The past year has seen a great deal of excitement in the field of breast cancer genetics. Since linkage of the familial breast-ovarian cancer gene (BRCA1) to chromosome 17, the critical region has been narrowed to 1.0-1.5 Mb by recombination studies, a detailed physical map has been constructed and much of the region has been cloned in yeast artificial chromosome, bacteriophage P1 and cosmid vectors. The focus now lies on identifying the genes housed within the BRCA1 region and scanning them for oncogenic mutations.

A case of acute monocytic leukemia with t(11;17) involving a rearrangement of MLL-1 and a region proximal to the RARA gene

A case of acute monocytic leukemia with t(11;17)(123;q11-21) arising in a 4-month-old boy is described. The breakpoint on chromosome 11 could be mapped to an 8-kb BamHI fragment within the MLL-1 gene, as seen in the majority of infant leukemias. In situ hybridization with cosmid probes allowed us to map the breakpoint on 17q proximal to the RARA gene, while Southern and Northern analyses showed that the gene was not disrupted by the translocation.