| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Molecular Biology and Genetics |
Department of Pediatrics [M. Y., B. A. F.], Genetics Laboratory [P. O.], Vermont Cancer Center [P. O., B. A. F.], Departments of Medical Biostatistics [P. M. V.] and Microbiology and Molecular Genetics [B. A. F.], University of Vermont, Burlington, Vermont 05405
| ABSTRACT |
|---|
|
|
|---|
| INTRODUCTION |
|---|
|
|
|---|
Recent studies have linked for the first time specific in utero genetic events and the development of cancer in children. Specifically, in utero somatic mutational events involving the MLL/AF4 (1 , 2) and TEL-AML1 (3 , 4) gene fusions in T cells and immunoglobulin heavy chain and T-cell receptor rearrangements in B cells (5) have been correlated with the subsequent development of infant and childhood leukemia.
Previously, we reported developmental and gender-specific differences in the in utero frequency of somatic mutations (Mf) at the HPRT3 reporter gene (6) . Specifically, the Mf of preterm newborns was higher compared with full-term newborns, with the mean Mf of female preterm newborns being inversely related to gestational age and significantly higher than that found for male preterm newborns (6) .
We report here a comparative analysis of the mutational spectra at the HPRT reporter gene mutations in T cells from this cohort. Statistical analyses revealed a significant increase of V(D)J recombinase-mediated HPRT deletions in preterm newborns compared with full-term infants. In addition, there was a significant increase in V(D)J recombinase-mediated deletions in both preterm and full-term female newborns compared with preterm and full-term male newborns. This gender-specific difference in V(D)J recombinase-mediated events may be relevant to understanding the higher incidence of infant leukemia observed among females.
| MATERIALS AND METHODS |
|---|
|
|
|---|
36 weeks; Ref. 7
) were acquired from the labor and delivery unit of Fletcher Allen Hospital of the University of Vermont College of Medicine. Informed consents were obtained after the procedure was approved by the Committee on Human Research at the University of Vermont.
HPRT T-Cell Cloning Assay.
Determination of HPRT Mf and the isolation of mutant clones were described previously (6
, 7)
. HPRT mutant isolates were expanded and stored at -80°C at either 1 x 104 cells for reverse transcription-PCR or 5 x 104 cells for genomic multiplex PCR before molecular analysis.
Molecular Analysis of HPRT Mutant Isolates.
The HPRT locus, located at Xq26, contains 9 exons, is 43 Kb in size, and has been completely sequenced. The coding sequence is 657-bp long. Molecular analyses of mutant cells both at the genomic and cDNA level have been well described (7, 8, 9)
. HPRT mutations observed previously include: (a) base substitutions at more that 270 sites in all nine exons; (b) small deletions and insertions; (c) large structural alterations; (d) splice site changes in introns; and (e) specialized genetic events such as V(D)J recombinase-mediated deletions (9, 10, 11)
.
Because the HPRT gene is located on the X-chromosome, molecular analysis at the DNA/RNA level is performed in different ways for mutant isolates from males and females (7) . Mutant isolates from males first were analyzed by multiplex genomic HPRT PCR to determine the presence or absence of the nine HPRT exons (8) . Mutant isolates from males showing no genomic alterations were characterized by reverse transcriptase-mediated production of HPRT cDNA, nested PCR amplification, and DNA sequencing of the amplified products (7) . The multiplex PCR primer pairs for exons 19 also permitted sequence analyses of both intron and exon segments involved in most splice-sequence mutations, reflected as exon exclusions or intron inclusions in cDNA. For mutant isolates from females, multiplex genomic PCR analysis was not performed because the inactive X chromosome precludes deletion determination. Therefore, HPRT mutant isolates from females first were analyzed with specific primers to screen for V(D)J recombinase-mediated exon 23 deletion mutants (11) . Then, those mutant isolates which showed no V(D)J recombinase-mediated deletions were analyzed by reverse transcription-PCR and DNA sequencing.
Statistical Analysis.
Logistic regression was used to assess the effects of gender and development on the proportions of the different types of mutations. Models with interaction terms were fitted to test whether the effects of gender and development were independent. In utero exposure to tobacco smoke was included in some models to determine whether the effects of development and gender were attributable to differences in transplacental exposure to tobacco smoke. Detailed information about maternal smoking and passive smoke exposure was unavailable for many preterm infants, so smoke exposure was represented as dichotomous variables (exposed or not exposed). All models included a random effect to account for the correlation between multiple mutations from the same newborn.
| RESULTS |
|---|
|
|
|---|
T); PS29 (deletion exon 2); PS5 (exclusion exons 26); MFS89 (deletion exons 19 and deletion exons 29); MFS36 (deletion exons 79); and MFS65 (G3
T). Mutational spectrum data for full-term infants was reported previously, except for those indicated in Table 1
|
|
|
|
Distribution analysis of small alterations revealed a higher proportion of transition mutations compared with transversion mutations in both preterm and full-term newborns. Logistic regression analysis of the proportions of transitions and transversions did not demonstrate a relationship with either development or gender.
There were two predominant large alterations observed: HPRT deletions of exons 2 and 3 mediated by V(D)J recombinase (V(D)J deletions) as defined previously (9
, 11)
, and exon deletions not mediated by V(D)J recombinase (non-V(D)J deletions). Distribution analysis revealed a higher proportion of V(D)J deletions compared with non-V(D)J deletions among all preterm infants and term females, but not among term males. Notably, logistic regression analysis revealed that the proportion of V(D)J deletions to non-V(D)J deletions was significantly related to both development and gender. Specifically, the proportion of V(D)J deletions were significantly higher compared with non-V(D)J deletions in preterm infants than full-term infants of the same gender (OR, 3.5; P = 0.012) as well as higher in females compared with males of the same developmental status (OR, 4.1; P = 0.043). Similar results were obtained when development was represented as gestational age rather than being classified as preterm or full-term, with ORs indicating that the proportion of V(D)J deletions increased
13% with each week of decreasing gestational age from birth (P = 0.038).
Previously, we have reported that transplacental exposure to tobacco smoke results in a significant increase in V(D)J-mediated HPRT deletions in healthy full-term infants (7) . In this study, an analysis of transplacental tobacco exposure was not related to any type of alteration in those preterm infants for whom exposure status was available.
Analysis of V(D)J Recombinase-mediated Breakpoints.
Characteristic V(D)J recombinase-mediated sequence signature markings for HPRT V(D)J deletions are summarized in Fig. 2
. A total of 10 V(D)J recombinase-mediated mutants from female preterm newborns and 21 V(D)J recombinase-mediated mutant isolates from male preterm newborns were characterized. All but two isolates from male subjects were Class I V(D)J deletion mutants, with the remaining mutant isolates being Class III V(D)J deletion mutants (9)
. There were five mutant isolates from male subjects and two mutant isolates from female subjects that lacked the N nucleotides additions. The percentage of the breakpoint sequences lacking the N nucleotide in the V(D)J mutant isolates from preterm newborns (22.6%, 7 of 31) was higher than the percentage observed previously for full-term newborns (5.6%; 1 of 18; Ref. 7
). In addition, two atypical V(D)J recombinase events were observed. The V(D)J deletion breakpoint sequence from PS7M11 contained a 14-base N nucleotide insertion with an unusually long 26-base nibbling at the 3' side of the breakpoint, whereas another mutation from subject PS7M20 contained a tandem direct repeat of a motif 5'-CACATCCCTTTCATG-3', which is separated by four bases upstream of the 5' breakpoint.
|
| DISCUSSION |
|---|
|
|
|---|
V(D)J recombinase-mediated rearrangements have been observed with cytogenetic alterations associated with T- and B-cell leukemia (13, 14, 15, 16) . In these studies, sequence analysis of translocation and deletion breakpoint sites in malignant clones demonstrated hallmark V(D)J recombinase signature markings that include palindromic bases (P nucleotides) and nucleotide nibbling and/or insertion of nontemplated bases (N nucleotides) at heptamer (CAC/TGTG)/nonamer (GGTTTTTGT) RSSs containing 12- and 23-bp spacers. Recently, chromosomal rearrangements involving the MLL (ALL-1, HRX-AF-9) gene at chromosome band 11q23 and the TEL-AML1 gene fusion in children with infant leukemia (<12 months of age) have been shown to have occurred in utero (3 , 17 , 18) . In addition, molecular analysis of Guthrie blood spots in monozygotic twins demonstrated clonal MLL fusion rearrangements that were subsequently identified in leukemic cells from these children, providing additional support to the hypothesis that in utero somatic mutational events are associated with the development of pediatric leukemia (1 , 19 , 20) . These and other studies in MLL-AF9 knockin mice (21) also demonstrate that other genetic events and environmental influences likely affect the length of the latent period for tumor development. For example, the expression of mutant isoforms of a transcription factor Ikaros has also been correlated with infant leukemia (22) . The etiology of a number of MLL rearrangements observed is not clear. Cell lines established from leukemia patients with t(4;11)(q21;q23) MLL translocations have showed the hallmarks of V(D)J recombinase at the chromosomal breakpoints, which include cryptic RSSs and random base insertions at chromosomal breakpoints (23) .
MLL rearrangements have also been associated with chemotherapy using topoisomerase II inhibitors (24 , 25) . These chemotherapeutic agents have been shown to increase the frequency of V(D)J recombinase-mediated HPRT deletions in the CCRF-CEM lymphoid cell line that constitutively expresses RAG1 and RAG2 (26) , therefore suggesting a link between DNA DSB repair and V(D)J recombinase-mediated rearrangements. In addition, some components of the DSB repair system are shared by V(D)J recombinase, including the catalytic subunit of DNA-dependent protein kinase (27) , Ku70 (28) , and Ku80 (29 , 30) . Breakpoints associated with some t(4;11) translocations involving MLL genes have recently been reported to display short tandem repeats, inversions, and short homologous sequences at the chromosomal breakpoints, suggesting a DNA repair mechanism (31 , 32) . Of interest, P nucleotide sequences were observed at some of these breakpoints, which may indicate that V(D)J recombinase activity may have also participated in these translocations.
In this report, 22.6% of V(D)J breakpoints in preterm newborns did not contain N nucleotide insertion compared with 5.6% in full-term newborns. A decrease in the insertion of N nucleotides has been associated with the early stages of murine B-cell (33)
and 
T-cell development (34)
as well as in human T-cell development attributable to decreased in utero expression of terminal deoxytransferase. The lower frequency of in utero N nucleotides we observed is in agreement with these previous reports. In addition, V(D)J mutant, PS7M20, contained a tandem repeat (5'-CACATCCCTTTCATG-3'). Such tandem repeats were also observed at MLL breakpoint sites (31
, 32)
.
Therefore, during in utero lymphoid development, a synergistic relationship may exist between components of the V(D)J recombinase and DSB repair systems that increases the frequency of aberrant genomic deletions and chromosome translocations that are responsible for the development of leukemia in infants and children.
| ACKNOWLEDGMENTS |
|---|
| FOOTNOTES |
|---|
1 Research was supported by Child Health and Human Development (NICHD) Grants 1K11HD01010 and 1R29HD35309, National Cancer Institute Grant 1KO1CA77737, and National Cancer Institute Grant P30CA22435 to the University of Vermont Cancer Center DNA Analysis Facility. ![]()
2 To whom requests for reprints should be addressed, at Department of Pediatrics, Medical Alumni Building, Burlington VT 05405. Phone: (802) 656-2296; Fax: (802) 656-2077; E-mail: finette{at}salus.med.uvm.edu ![]()
3 The abbreviations used are: HPRT, hypoxanthine-guanine phosphoribosyltransferase; Mf, mutation frequency; RSS, recombination signal sequences; OR, odds ratio; N nucleotides, nontemplated nucleotides; DSB, double-strand break. ![]()
Received 11/15/00. Accepted 2/13/01.
| REFERENCES |
|---|
|
|
|---|
/ß lineage: T-cell receptor
gene deletion mechanism affects multiple genes. J. Exp. Med., 177: 965-977, 1993.
genes: implications for 
T-cell lineages and for a novel intermediate of V-(D)-J joining. Cell, 59: 859-870, 1989.[Medline]
This article has been cited by other articles:
![]() |
J. M. Murray, J. P. O'Neill, T. Messier, J. Rivers, V. E. Walker, B. McGonagle, L. Trombley, L. G. Cowell, G. Kelsoe, F. McBlane, et al. V(D)J Recombinase-Mediated Processing of Coding Junctions at Cryptic Recombination Signal Sequences in Peripheral T Cells during Human Development J. Immunol., October 15, 2006; 177(8): 5393 - 5404. [Abstract] [Full Text] [PDF] |
||||
![]() |
H. E. Kendall, P. M. Vacek, J. L. Rivers, S. C. Rice, T. L. Messier, and B. A. Finette Analysis of Genetic Alterations and Clonal Proliferation in Children Treated for Acute Lymphocytic Leukemia. Cancer Res., September 1, 2006; 66(17): 8455 - 8461. [Abstract] [Full Text] [PDF] |
||||
![]() |
J. L. Wiemels, Z. Xiao, P. A. Buffler, A. T. Maia, X. Ma, B. M. Dicks, M. T. Smith, L. Zhang, J. Feusner, J. Wiencke, et al. In utero origin of t(8;21) AML1-ETO translocations in childhood acute myeloid leukemia Blood, May 15, 2002; 99(10): 3801 - 3805. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| Cancer Research | Clinical Cancer Research |
| Cancer Epidemiology Biomarkers & Prevention | Molecular Cancer Therapeutics |
| Molecular Cancer Research | Cancer Prevention Research |
| Cancer Prevention Journals Portal | Cancer Reviews Online |
| Annual Meeting Education Book | Meeting Abstracts Online |