Michelle M. LeBeau

MLL3 Is a Haploinsufficient 7q Tumor Suppressor in Acute Myeloid Leukemia

Recurring deletions of chromosome 7 and 7q [-7/del(7q)] occur in myelodysplastic syndromes and acute myeloid leukemia (AML) and are associated with poor prognosis. However, the identity of functionally relevant tumor suppressors on 7q remains unclear. Using RNAi and CRISPR/Cas9 approaches, we show that an ∼50% reduction in gene dosage of the mixed lineage leukemia 3 (MLL3) gene, located on 7q36.1, cooperates with other events occurring in -7/del(7q) AMLs to promote leukemogenesis. Mll3 suppression impairs the differentiation of HSPC. Interestingly, Mll3-suppressed leukemias, like human -7/del(7q) AMLs, are refractory to conventional chemotherapy but sensitive to the BET inhibitor JQ1. Thus, our mouse model functionally validates MLL3 as a haploinsufficient 7q tumor suppressor and suggests a therapeutic option for this aggressive disease.

Nineteen cases of the t(1;22)(p13;q13) acute megakaryblastic leukaemia of infants/children and a review of 39 cases: report from a t(1;22) study group.

Nineteen cases of the t(1;22)(p13;q13) acute megakaryblastic leukaemia of infants/children and a review of 39 cases: report from a t(1;22) study group

Context-Dependent Hormone-Refractory Progression Revealed through Characterization of a Novel Murine Prostate Cancer Cell Line

Insights into the molecular basis of hormone-refractory prostate cancer have principally relied on human prostate cancer cell lines, all of which were derived from patients who had already failed hormonal therapy. Recent progress in developing genetically engineered mouse prostate cancer models provides an opportunity to isolate novel cell lines from animals never exposed to hormone ablation, avoiding any potential bias conferred by the selective pressure of the castrate environment. Here we report the isolation of such a cell line (Myc-CaP) from a c-myc transgenic mouse with prostate cancer. Myc-CaP cells have an amplified androgen receptor gene despite no prior exposure to androgen withdrawal and they retain androgen-dependent transgene expression as well as androgen-dependent growth in soft agar and in mice. Reexpression of c-Myc from a hormone-independent promoter rescues growth in androgen-depleted agar but not in castrated mice, showing a clear distinction between the molecular requirements for hormone-refractory growth in vitro versus in vivo. Myc-CaP cells represent a unique reagent for dissecting discreet steps in hormone-refractory prostate cancer progression and show the general utility of using genetically engineered mouse models for establishing new prostate cancer cell lines.

Localization of prostate cancer metastasis-suppressor activity on human chromosome 17

Prostate cancer is the most commonly diagnosed malignancy in American men. Currently, it is difficult to accurately predict the clinical course of histologically localized prostatic cancer in the individual patient. Identification of markers for metastatic potential of prostate cancer may improve the diagnosis and treatment of this disease. We have previously demonstrated that human chromosome 17 (17pter–q23) suppresses the metastatic ability of AT6.1 rat prostatic cancer cells. In this study we report on the further localization of the metastasis suppressor activity encoded by human chromosome 17.

Acute myeloid leukaemia in a patient with Seckel syndrome.

We report a female patient with Seckel syndrome who developed acute myeloid leukaemia at the age of 26 years. Analysis of bone marrow chromosomes showed an abnormal clone with abnormalities involving multiple chromosomes, including monosomy 7, trisomy 8, trisomy 11, and loss of the long arm of chromosome 5. After treatment with chemotherapy, the patient experienced severe toxicity with profound bone marrow aplasia and died of pneumonia two months later. We suggest that patients with Seckel syndrome may be at risk of developing myelodysplasia and acute myeloid leukaemia. They may also have poor tolerance to cytotoxic therapy.

Analysis of the t(6;11)(q27;q23) in leukemia shows a consistent breakpoint in AF6 in three patients and in the ML‐2 cell line

The t(6;11)(q27;q23) is one of the most common translocations observed in patients with acute myeloid leukemia (AML). The translocation breakpoint involves the MLL gene, which is the human homolog of the Drosophila trithorax gene, at 11q23 and the AF6 gene at 6q27. Reverse transcriptase‐polymerase chain reaction (RT‐PCR) using an MLL sense primer and an AF6 antisense primer detected the MLL/AF6 fusion cDNA from three leukemia patients with the t(6;11) [two AML and one T‐acute lymphoblastic leukemia (ALL)] and one cell line. The fusion point in the AF6 cDNA from these cases is identical, regardless of the leukemia phenotype. The ML‐2 cell line, which was established from a patient with AML that developed after complete remission of T‐cell lymphoma, has retained an 11q23–24 deletion from the lymphoma stage and has acquired the t(6;11) with development of AML. The ML‐2 cells have no normal MLL gene on Southern blot analysis, which indicates that an intact MLL gene is not necessary for survival of leukemic cells. Genes Chromosom Cancer 15:206–216 (1996).

Gonadal and statural determinants on the X chromosome and their relationship to in vitro studies showing prolonged cell cycles in 45,X; 46,X,del(X)(p11); 46,X,del(X)(q13); and 46,X,del(X)(q22) fibroblasts

Correlation of clinical features with cytogenetic abnormalities for individuals showing deletions of the X short arm (Xp) or the X long arm (Xq) indicate the following: (1) both Xp and Xq are necessary to assure normal ovarian development, although (2) persisting ovarian function is not infrequently associated with either (del(X)(p11) or del(Xq)(13,21,22, or 24). (3) Ovarian determinants on Xp are localized to region Xp11, but determinants on Xq cannot be precisely localized. (4) Both Xp and Xq contain statural determinants, the former localized to region Xp21 leads to Xpter. Both cell generation time and phases of the cell cycle were studied to test the hypothesis that the short stature, intrauterine growth retardation, and high embryonic lethality of 45,X can be explained on the basis of intrinsic retardation of cell division (i.e., prolonged cell cycle). Cell generation times of four 45,X fibroblast lines were significantly longer than those of for normal diploid lines, a difference accounted for by a prolonged S phase. 46,X,del(X)(p11), 46,X,del(X)(q13), and 46,X,del(X)(q22) lines also showed increased cell generation times when compared to 46,XX lines.

Human glutamine: fructose-6-phosphate amidotransferase: characterization of mRNA and chromosomal assignment to 2p13

It has been previously shown that some toxic effects of high concentrations of glucose are mediated by the hexosamine biosynthesis pathway and its rate-limiting enzyme glutamine:fructose-6-phosphate amidotransferase (GFA). We have used the cloned human GFA cDNA to study the chromosomal localization of the gene and tissue distribution of mRNA. The human GFA gene is on chromosome 2, band p13 as determined by fluorescence in situ hybridization. An 8-kb species of GFA mRNA was detected in all rat tissues tested with relatively high expression in testis and smooth muscle; a unique 3-kb mRNA species was found only in testis.

Chromosome analysis of ectopic human conceptuses

Maternal factors (e.g. salpingitis) are known to be associated with ectopic gestations; however, few studies have considered the chromosomal complements or morphologic features of ectopic conceptuses. We studied 23 ectopic conceptuses removed from fallopian tubes during surgical resection. The chromosomal complements were normal (four with 46,XY; four with 46,XX) in all cases in which an intact embryo was identified, as well as in the single case characterized by disorganized embryonic tissue. Ten of the 14 ectopic conceptuses in which only a gestational sac and placental villi were identified also show normal chromosomal complements (seven with 46,XX; three with 46,XY); in the remaining four cases, variations from the normal chromosomal complement were found (46,XX/47,XX,+9; 45,X/46,XX; 46,XX/47,XX,+mar; and 92,XXXX). The former two probably signify underlying fetal abnormalities; however, the latter two could have reflected, respectively, in vitro aberrations or tetraploidy characteristic of normal amnion. Pooled data from this study and two previous reports indicate that ectopic conceptuses probable have no higher frequency of chromosomal abnormalities than in utero conceptuses of comparable embryonic ages.

Search for a Third Susceptibility Gene for Maturity-Onset Diabetes of the Young: Studies With Eleven Candidate Genes

Maturity-onset diabetes of the young (MODY) is a model for genetic studies of non-insulin-dependent diabetes mellitus. We have identified 15 MODY families in which diabetes is not the result of mutations in the glucokinase gene. This cohort of families will be useful for identifying other diabetes-susceptibility genes. Nine other candidate genes potentially implicated in insulin secretion or insulin action have been tested for linkage with MODY in these families, including glucokinase regulatory protein, hexokinase II, insulin receptor substrate 1, fatty acid–binding protein 2, glucagon-like peptide-1 receptor, apolipoprotein C-II, glycogen synthase, adenosine deaminase (a marker for the MODY gene on chromosome 20), and phosphoenolpyruvate carboxykinase. None of these loci showed evidence for linkage with MODY, implying that mutations in these genes do not make a major genetic contribution to the development of MODY. In addition to these linkage analyses, one or two affected subjects from each family were screened for the presence of the A to G mutation at nucleotide 3,243 of the mitochondrial tRNALeu(UUR) gene. This mutation was not found in any of these subjects. Finally, we report the localization of the gene encoding the regulatory protein of glucokinase to chromosome 2, band p22.3 and the identification of a restriction fragment length polymorphism at this locus.