Influence of a nonfragile FHIT transgene on murine tumor susceptibility

FHIT, at a constitutively active chromosome fragile site, is often a target of chromosomal aberrations and deletion in a large fraction of human tumors. Inactivation of murine Fhit allelessignificantly increases susceptibility of mice to spontaneous and carcinogen-induced tumorigenesis. In this study, transgenic mice, carrying a human FHIT cDNA under control of the endogenous promoter, were produced to determine the effect of Fhit expression, from a nonfragile cDNA transgene outside the fragile region, on carcinogen-induced tumor susceptibility of wildtype and Fhit heterozygous mice. Mice received sufficient oral doses of N-nitrosomethybenzylamine (NMBA) to cause forestomach tumors in >80% of nontransgenic control mice. Although the level of expression of the FHIT transgene in the recombinant mouse strains was much lower than the level of endogenous Fhit expression, the tumor burden in NMBA-treated male transgenic mice was significantly reduced, while female transgenic mice were not protected. To determine if the difference in protection could be due to differences in epigenetic changes at the transgene loci in male versus female mice, we examined expression, hypermethylation and induced re-expression of FHIT transgenes in male and female mice or cells derived from them. The transgene was methylated in male and female mice and in cell lines established from male and female transgenic kidneys, the FHIT locus was both hypermethylated and deacetylated. It is likely that the FHIT transgene is more tightly silenced in female transgenic mice, leading to a lack of protection from tumor induction.

Murine Spam1 mRNA: involvement of AU-rich elements in the 3'UTR and antisense RNA in its tight post-transcriptional regulation in spermatids

Sperm adhesion molecule1 (SPAM1), the best characterized hyaluronidase gene, is abundantly expressed in the testis. We attempted to overexpress mouse Spam1 via transgenesis using either the endogenous promoter in a BAC or a heterologous Protamine1 promoter for a Spam1 cDNA transgene. Although transgene-copy numbers ranged from 2 to 15 and transgenic transcripts were expressed, there was a general failure of overexpression of the RNA and protein in the testis of all seven founders. Also, three transgenic lines showed a modest downregulation or co-suppression of the RNA for Spam1 and Hyal5, present on the BAC. We provide evidence for the potential involvement of two co-ordinating post-transcriptional regulatory processes in the failure of overexpression: abundant endogenous antisense RNA and adenosine-uridine (AU)-rich element-mediated regulation of RNA turnover. We demonstrate that AU-rich elements (AREs) in the 3'UTR of mRNAs, well-known to interact with trans-acting proteins to target the RNA for (in)stability, are present in Spam1 RNA and specifically bind to six testicular cytoplasmic proteins. These AU-binding proteins (AUBPs) were virtually absent from the kidney where transcripts are rare, and were shown to interact with the cytoskeleton, which modulates mRNA turnover. In addition to a role in the RNAi pathway, antisense RNA can also modulate ARE-mediated regulation of mRNA by hybridizing to the AREs and specifically silencing their function. This potentially links the two processes in the regulation of Spam1 expression. We hypothesize that testicular Spam1 RNA is regulated post-transcriptionally by cis-acting ARE(s) in the 3'UTR which recognize AUBPs and which are modulated by antisense transcripts.

Homozygous carnitine palmitoyltransferase 1a (liver isoform) deficiency is lethal in the mouse

To better understand carnitine palmitoyltransferase 1a (liver isoform, gene=Cpt-1a, protein=CPT-1a) deficiency in human disease, we developed a gene knockout mouse model. We used a replacement gene targeting strategy in ES cells that resulted in the deletion of exons 11-18, thus producing a null allele. Homozygous deficient mice (CPT-1a -/-) were not viable. There were no CPT-1a -/- pups, embryos or fetuses detected from day 10 of gestation to term. FISH analysis demonstrated targeting vector recombination at the expected single locus on chromosome 19. The inheritance pattern from heterozygous matings was skewed in both C57BL/6NTac, 129S6/SvEvTac (B6;129 mixed) and 129S6/SvEvTac (129 coisogenic) genetic backgrounds biased toward CPT-1a +/- mice (>80%). There was no sex preference with regard to germ-line transmission of the mutant allele. CPT-1a +/- mice had decreased Cpt-1a mRNA expression in liver, heart, brain, testis, kidney, and white fat. This resulted in 54.7% CPT-1 activity in liver from CPT-1a +/- males but no significant difference in females as compared to CPT-1a +/+ controls. CPT-1a +/- mice showed no fatty change in liver and were cold tolerant. Fasting free fatty acid concentrations were significantly elevated, while blood glucose concentrations were significantly lower in 6-week-old CPT-1a +/- mice compared to controls. Although the homozygous mutants were not viable, we did find some aspects of haploinsufficiency in the CPT-1a +/- mutants, which will make them an important mouse model for studying the role of CPT-1a in human disease.

Spam1-associated transmission ratio distortion in mice: elucidating the mechanism

BACKGROUND

While transmission ratio distortion, TRD, (a deviation from Mendelian ratio) is extensive in humans and well-documented in mice, the underlying mechanisms are unknown. Our earlier studies on carriers of spontaneous mutations of mouse Sperm Adhesion Molecule 1 (Spam1) suggested that TRD results from biochemically different sperm, due to a lack of transcript sharing through the intercellular cytoplasmic bridges of spermatids. These bridges usually allow transcript sharing among genetically different spermatids which develop into biochemically and functionally equivalent sperm.

OBJECTIVES

The goals of the study were to provide support for the lack of sharing (LOS) hypothesis, using transgene and null carriers of Spam1, and to determine the mechanism of Spam1-associated TRD.

METHODS

Carriers of Spam1-Hyal5 BAC transgenes were mated with wild-type female mice and the progeny analyzed for TRD by PCR genotyping. Sperm from transgene and Spam1 null carriers were analyzed using flow cytometry and immunocytochemistry to detect quantities of Spam1 and/or Hyal5. Transgene-bearing sperm with Spam1 overexpression were detected by fluorescence in situ hybridization. In wild-type animals, EM studies of in situ transcript hybridization of testis sections and Northern analysis of biochemically fractionated testicular RNA were performed to localize Spam1 transcript. Finally, AU-rich motifs identified in the 3' UTR of Spam1 RNA were assayed by UV cross-linking to determine their ability to interact with testicular RNA binding proteins.

RESULTS

The Tg8 line of transgene carriers had a significant (P < 0.001) TRD, due to reduced fertilizing ability of transgene-bearing sperm. These sperm retained large cytoplasmic droplets engorged with overexpressed Spam1 or Hyal5 protein. Caudal sperm from transgene carriers and caput sperm of null carriers showed a bimodal distribution of Spam1, indicating that the sperm in a male were biochemically different with respect to Spam1 quantities. Spam1 RNA was absent from the bridges, associated exclusively with the ER, and was shown to be anchored to the cytoskeleton. This compartmentalization of the transcript, mediated by cytoskeletal binding, occurs via protein interactions with 3' UTR AU-rich sequences that are likely involved in its stabilization.

CONCLUSION

We provide strong support for the LOS hypothesis, and have elucidated the mechanism of Spam1-associated TRD.

Fhit-deficient normal and cancer cells are mitomycin C and UVC resistant

To identify functions of the fragile tumour suppressor gene, FHIT, matched pairs of Fhit-negative and -positive human cancer cell clones, and normal cell lines established from Fhit −/− and +/+ mice, were stressed and examined for differences in cell cycle kinetics and survival. A larger fraction of Fhit-negative human cancer cells and murine kidney cells survived treatment with mitomycin C or UVC light compared to matched Fhit-positive cells; ∼10-fold more colonies of Fhit-deficient cells survived high UVC doses in clonigenic assays. The human cancer cells were synchronised in G1, released into S and treated with UVC or mitomycin C. At 18 h post mitomycin C treatment ∼6-fold more Fhit-positive than -negative cells had died, and 18 h post UVC treatment 3.5-fold more Fhit-positive cells were dead. Similar results were obtained for the murine −/− cells. After low UVC doses, the rate of DNA synthesis in −/− cells decreased more rapidly and steeply than in +/+ cells, although the Atr–Chk1 pathway appeared intact in both cell types. UVC surviving Fhit −/− cells appear transformed and exhibit >5-fold increased mutation frequency. This increased mutation burden could explain the susceptibility of Fhit-deficient cells in vivo to malignant transformation.

High efficiency creation of human monoclonal antibody-producing hybridomas

The native human antibody repertoire holds unexplored potential for the development of novel monoclonal antibody therapeutics. Current techniques that fuse immortal cells and primary B-lymphocytes are sub-optimal for the routine production of hybridomas that secrete human monoclonal antibodies. We have found that a murine cell line that ectopically expresses murine interleukin-6 (mIL-6) and human telomerase (hTERT) efficiently forms stable human antibody-secreting heterohybridomas through cell fusion with primary human B-lymphocytes. The hybrid cells maintain secretion of human antibodies derived from the primary B-lymphocytes through multiple rounds of cloning. Using splenic B-lymphocytes from a patient immunized with a Streptococcus pneumoniae capsular polysaccharide vaccine, we have succeeded in creating hybridomas that secrete human monoclonal antibodies specific for S. pneumoniae antigens. Using peripheral blood lymphocytes, we have similarly cloned a human antibody that binds a viral antigen. These experiments establish that SP2/0-derived cell lines ectopically expressing mIL-6 and hTERT will enable the rapid cloning of native human monoclonal antibodies.

Partial paternal uniparental disomy of chromosome 6 in an infant with neonatal diabetes, macroglossia, and craniofacial abnormalities

Neonatal diabetes, which can be transient or permanent, is defined as hyperglycemia that presents within the first month of life and requires insulin therapy. Transient neonatal diabetes mellitus has been associated with abnormalities of the paternally inherited copy of chromosome 6, including duplications of a portion of the long arm of chromosome 6 and uniparental disomy, implicating overexpression of an imprinted gene in this disorder. To date, all patients with transient neonatal diabetes mellitus and uniparental disomy have had complete paternal isodisomy. We describe a patient with neonatal diabetes, macroglossia, and craniofacial abnormalities, with partial paternal uniparental disomy of chromosome 6 involving the distal portion of 6q, from 6q24-qter. This observation demonstrates that mitotic recombination of chromosome 6 can also give rise to uniparental disomy and neonatal diabetes, a situation similar to that observed in Beckwith-Wiedemann syndrome, another imprinted disorder. This finding has clinical implications, since somatic mosaicism for uniparental disomy of chromosome 6 should also be considered in patients with transient neonatal diabetes mellitus.

Murine chromosome 16 telomeric region, homologous with human chromosome 21q22, contains the osmoregulatory Na(+)/myo-inositol cotransporter (SLC5A3) gene

The murine Na(+)/myo-inositol cotransporter (SLC5A3) gene (Slc5a3) was cloned, the restriction sites mapped, and the coding region sequenced. Similar to other mammalian counterparts, including human, the gene has a single coding exon, with an open reading frame of 2.2 kb. The predicted protein of 718 amino acids is also highly conserved, compared to other mammalian homologs. Using fluorescence in situ hybridization, Slc5a3 was localized to the telomeric region of mouse chromosome 16, which is syntenic to human chromosome 21q22. An increased Slc5a3 copy number may explain the increased levels of myo-inositol in the brains of trisomy 16 mice and the increased rate of transport of myo-inositol into cultured neurons derived from trisomy 16 mice.

The human homologue of the yeast proteins Skb1 and Hsl7p interacts with Jak kinases and contains protein methyltransferase activity

To expand our understanding of the role of Jak2 in cellular signaling, we used the yeast two-hybrid system to identify Jak2-interacting proteins. One of the clones identified represents a human homologue of the Schizosaccaromyces pombe Shk1 kinase-binding protein 1, Skb1, and the protein encoded by the Saccharomyces cerevisiae HSL7 (histone synthetic lethal 7) gene. Since no functional motifs or biochemical activities for this protein or its homologues had been reported, we sought to determine a biochemical function for this human protein. We demonstrate that this protein is a protein methyltransferase. This protein, designated JBP1 (Jak-binding protein 1), and its homologues contain motifs conserved among protein methyltransferases. JBP1 can be cross-linked to radiolabeled S-adenosylmethionine (AdoMet) and methylates histones (H2A and H4) and myelin basic protein. Mutants containing substitutions within a conserved region likely to be involved in AdoMet binding exhibit little or no activity. We mapped the JBP1 gene to chromosome 14q11.2-21. In addition, JBP1 co-immunoprecipitates with several other proteins, which serve as methyl group acceptors and which may represent physiological targets of this methyltransferase. Messenger RNA for JBP1 is widely expressed in human tissues. We have also identified and sequenced a homologue of JBP1 in Drosophila melanogaster. This report provides a clue to the biochemical function for this conserved protein and suggests that protein methyltransferases may have a role in cellular signaling.

Molecular studies of an ependymoma-associated constitutional t(1;22)(p22;q11.2)

We previously described a patient with a de novo constitutional translocation, t(1;22)(p22;q11.2), who developed a malignant ependymoma at age 5, and we proposed that the translocation predisposed the child to the development of the tumor. As a step toward isolation of a putative cancer gene, we have characterized the breakpoints of the (1;22) translocation at the molecular level. The chromosome 22 breakpoint has been narrowed to a region between ARVCF and D22S264. The chromosome 1 breakpoint has been mapped onto a doubly-linked Whitehead YAC contig by PCR analysis of the STS contents of the patient's derivative chromosomes isolated in somatic cell hybrids. Loss-of-heterozygosity (LOH) studies of the patient's ependymoma and of sporadic ependymomas showed no evidence of consistent loss in the breakpoint regions, suggesting that activation of an oncogene, rather than inactivation of a tumor suppressor gene, is the more likely molecular mechanism involved in this case. The gene for Edg-1, a neurally expressed, seven-segment transmembrane receptor, maps to the region of the chromosome 1 breakpoint but does not appear to be interrupted by the translocation. Molecular characterization of the breakpoint regions reported here represents an important step in the identification of the gene(s) affected by this translocation.

High-resolution genetic map of the human glutamyl aminopeptidase gene (ENPEP)

The murine B-lymphocyte differentiation antigen BP-1/6C3 has been identified as glutamyl aminopeptidase (EAP), the gene symbol for which is ENPEP. Using genomic DNA encoding for human EAP as a probe, we identified the ENPEP gene location on human chromosome 4q25 by polymerase chain reaction analysis of a human/rodent somatic cell hybrid mapping panel and by fluorescence in situ hybridization. Using a radiation hybrid panel, the gene order around ENPEP was determined to be centromere-D4S1236-(570 kb)-ENPEP-(210 kb)-D4S262-(270 kb)-D4S953-(270 kb)-D4S474-(570 kb)-IF. The linkage of ENPEP to complement factor I (IF) confirms the human chromosome band 4q25 localization predicted from the chromosomal location of murine ENPEP. Human ENPEP thus provides an additional marker for the long arm of chromosome 4 that should facilitate studies of this genomic region.

Integration of physical, breakpoint and genetic maps of chromosome 22. Localization of 587 yeast artificial chromosomes with 238 mapped markers

Detailed physical maps of the human genome are important resources for the identification and isolation of disease genes and for studying the structure and function of the genome. We used data from STS content mapping of YACs and natural and induced chromosomal breakpoints to anchor contigs of overlapping yeast artificial chromosome (YAC) clones spanning extensive regions of human chromosome 22. The STSs were assigned to specific regions (bins) on the chromosome using cell lines from a somatic hybrid mapping panel defining a maximum of 25 intervals. YAC libraries were screened by PCR amplification of hierarchical pools of yeast DNA with 238 markers, and a total of 587 YAC clones were identified. These YACs were assembled into contigs based upon their shared STS content using a simulated annealing algorithm. Fifteen contigs, containing between 2 and 74 STSs were assembled, and ordered along the chromosome based upon the cytogenetic breakpoint, meiotic and PFG maps. Additional singleton YACs were assigned to unique chromosomal bins. These ordered YAC contigs will be useful for identifying disease genes and chromosomal breakpoints by positional cloning and will provide the foundation for higher resolution physical maps for large scale sequencing of the chromosome.

Structure, chromosomal localization, and methylation pattern of the human mb-1 gene

The Ag receptor on B lymphocytes is a multimeric complex that is composed of an Ag-specific component, surface Ig, which is noncovalently associated with at least two other proteins, Ig alpha and Ig beta. These are the glycoprotein products of the B lineage-restricted mb-1 and B29 genes and are crucial for the cell surface expression and function of the Ag receptor on B lymphocytes. To better understand the regulation of mb-1, we have cloned and sequenced a 5.7-kb genomic DNA fragment that contained the human gene. The overall structure of human mb-1 is very similar to that of the murine gene, including the number and approximate size of exons. The promoter region lacks a TATA element, but contains two copies of an early B cell factor-binding motif, which previously has been shown to be important for murine mb-1 expression. Other structural features include two nuclear factor-kappa B binding sites at the 5' end of the gene and a long stretch of AG rich-sequence between exons 3 and 4, downstream of an Alu repeat sequence that contains a potential stem-loop structure. The mb-1 gene was localized to chromosome 19q13.2-13.3 by a combination of two methods, PCR amplification of DNA from a somatic cell hybrid-mapping panel and fluorescence in situ hybridization. An examination of the methylation pattern revealed a striking correlation between demethylation in the 5' region of the gene and expression of mb-1. The demethylated HpaII/MspI sites are adjacent to the nuclear factor-kappa B-binding motifs, which suggests a role for this transcription factor in the regulation of human mb-1 gene expression.

Structure, chromosomal localization, and methylation pattern of the human mb-1 gene

The Ag receptor on B lymphocytes is a multimeric complex that is composed of an Ag-specific component, surface Ig, which is noncovalently associated with at least two other proteins, Ig alpha and Ig beta. These are the glycoprotein products of the B lineage-restricted mb-1 and B29 genes and are crucial for the cell surface expression and function of the Ag receptor on B lymphocytes. To better understand the regulation of mb-1, we have cloned and sequenced a 5.7-kb genomic DNA fragment that contained the human gene. The overall structure of human mb-1 is very similar to that of the murine gene, including the number and approximate size of exons. The promoter region lacks a TATA element, but contains two copies of an early B cell factor-binding motif, which previously has been shown to be important for murine mb-1 expression. Other structural features include two nuclear factor-kappa B binding sites at the 5' end of the gene and a long stretch of AG rich-sequence between exons 3 and 4, downstream of an Alu repeat sequence that contains a potential stem-loop structure. The mb-1 gene was localized to chromosome 19q13.2-13.3 by a combination of two methods, PCR amplification of DNA from a somatic cell hybrid-mapping panel and fluorescence in situ hybridization. An examination of the methylation pattern revealed a striking correlation between demethylation in the 5' region of the gene and expression of mb-1. The demethylated HpaII/MspI sites are adjacent to the nuclear factor-kappa B-binding motifs, which suggests a role for this transcription factor in the regulation of human mb-1 gene expression.

Assignment of sterol carrier protein X/sterol carrier protein 2 to 1p32 and its exclusion as the causative gene for infantile neuronal ceroid lipofuscinosis

In the positional cloning of a disease gene with an unknown protein defect a spectrum of molecular biological methods is applied after linkage has been established. It is reasonable to analyze in detail any relevant candidate gene mapping to the particular chromosomal region. We report here the refined chromosomal assignment of SCPx/SCP2, a gene coding for the protein that is believed to have an important role in lipid metabolism by transporting many kinds of lipid molecules between organelles. This gene represents an excellent candidate gene for infantile neuronal ceroid lipofuscinosis, earlier assigned to 1p32 by us, since lipid metabolism in the patient's brain appears to be significantly disturbed. Expression and structural analyses by Northern, Southern and Western blotting as well as SSCP and direct sequencing did not detect any differences between the cDNAs of patients and controls. Consequently, it is unlikely that a mutation in SCPx/SCP2 is the underlying cause of this severe neurodegenerative disease of childhood.

Localization of the expressed human p58 protein kinase chromosomal gene to chromosome 1p36 and a highly related sequence to chromosome 15

The gene for the human p58 protein kinase, a cell division control-related gene, has been mapped by somatic cell hybrid analyses, in situ localization with the chromosomal gene, and nested polymerase chain reaction amplification of microdissected chromosomes. These studies indicate that the expressed p58 chromosomal gene maps to 1p36, while a highly related p58 sequence of unknown nature maps to chromosome 15. Assignment of a p34cdc2-related gene to 1p36 may have implications for numerous tumors that involve deletion of this region, including neuroblastoma, ductal carcinoma of the breast, malignant melanoma, Merkel cell carcinoma, and endocrine neoplasia.