Structure, expression profile and alternative processing of the human phosphatidylethanolamine N-methyltransferase (PEMT) gene

Phosphatidylethanolamine N-methyltransferase (PEMT) catalyzes the conversion of phosphatidylethanolamine (PE) to phosphatidylcholine (PC) in a series of three methylation reactions. Preliminary studies of PEMT in humans led to the cloning of three cDNAs each of which has a different 5' untranslated region (5'UTR). To determine the origin of PEMT splice variants and to investigate expression of the gene in human liver, we isolated a bacterial artificial chromosome (BAC) clone containing the full-length human gene. Each of the three unique untranslated first exons is present in a contiguous array in the gene, confirming the integrity of the cDNAs and alternative processing of PEMT transcripts. Human liver, heart and testis contain the highest levels of PEMT transcripts and of these, liver has the greatest PEMT expression. Furthermore, each of the three PEMT transcripts is present in varying abundance in liver whereas heart and testis contain only one and two transcripts, respectively. Thus, differential promoter usage in the human PEMT gene generates three unique transcripts and confers a tissue-specific expression pattern.

Identification of three novel cDNAs for human phosphatidylethanolamine N-methyltransferase and localization of the human gene on chromosome 17p11.2

Phosphatidylethanolamine is converted to phosphatidylcholine in mammalian liver by the enzyme phosphatidylethanolamine N-methyltransferase (PEMT). A form of the enzyme (PEMT2) has been isolated from rat liver, the cDNA cloned and expressed and the murine gene has been characterized and disrupted. Several lines of evidence suggested that PEMT2 might have a role in hepatocyte proliferation and liver cancer. Hence, we decided to investigate the human form of the enzyme. Unexpectedly, we cloned and expressed three novel human cDNAs encoding PEMT2. These forms differ from each other in the 5'-region with the point of divergence being 15 nucleotides upstream of the putative translation initiation codon. The remainder of the three cDNAs was identical. Expression of the coding region of the cDNAs in McArdle rat hepatoma cells resulted in three stable cell lines that showed a 27- to 115-fold elevation of PEMT activity compared to vector-transfected control cell lines. Screening of somatic cell hybrid panels, radiation hybrid panel mapping and fluorescent in situ hybridization mapping localized the human gene for PEMT2 to chromosome 17p11.2. The identification of three different human cDNAs for PEMT2 suggests that understanding the function of PEMT2 will be more complicated than anticipated.

Acute lymphoblastic leukemia with the (8;14)(q24;q32) translocation and FAB L3 morphology associated with a B-precursor immunophenotype: the Pediatric Oncology Group experience

Five pediatric patients are described with acute lymphoblastic leukemia (ALL) who at presentation had clinical findings suggestive of B cell ALL and lymphoblasts with FAB L3 morphology and the characteristic t(8;14)(q24;q32). However, the leukemia cells of all five patients failed to express surface immunoglobulin (sIg) and kappa or lambda light chains. Based on initial immunophenotyping results consistent with B-precursor ALL, four of these cases were initially treated with conventional ALL chemotherapy. These four patients were switched to B cell ALL treatment protocols once cytogenetic results became available revealing the 8;14 translocation. The fifth case was treated with B cell ALL therapy from the outset. Four of the five patients are in complete remission at 64, 36, 29 and 13 months from diagnosis. One patient relapsed and died 6 months after initial presentation. These five unusual cases with clinical B cell ALL, the t(8;14), and FAB L3 morphology, but negative sIg, demonstrate the importance of careful and multidisciplinary evaluation of leukemic cells with morphology, cytochemistry, immunophenotyping and cytogenetic analysis. Future identification of patients with this profile will allow us to expand our knowledge regarding prognostic significance and optimal treatment for this rare subgroup of patients.

Detection of Epstein-Barr virus in transformations of low-grade B-cell lymphomas after fludarabine treatment

Fludarabine is a highly effective chemotherapeutic agent for chronic lymphocytic leukemia/small lymphocytic lymphoma and is also active in other B-cell lymphoproliferative disorders. Although highly efficacious in destroying the malignant B-cells, fludarabine also causes T-cell lymphopenia and immunosuppression. We present five patients given fludarabine for low-grade B-cell lymphoproliferative disorders who showed transformation of the primary neoplasm to a higher grade tumor. Immunohistologic antibody studies were performed on paraffin-embedded tissue sections of the initial tissue (when available) and on the follow-up biopsy specimens for CD20, CD3, CD45RO, CD43, CD30, CD15, and latent membrane protein (LMP-1) for Epstein-Barr virus (EBV). The initial diagnoses in these five patients included chronic lymphocytic leukemia/small lymphocytic lymphoma (three cases), follicle center lymphoma (one case), and Waldenstrom's macroglobulinemia (one case). All of the follow-up biopsy specimens showed scattered Hodgkin's-like cells, and two of the five also showed foci of large-cell transformation. The Hodgkin's-like cells showed CD30 immunoreactivity in four of the five cases and CD15 immunoreactivity in three of the five. Strong immunoreactivity of the large, atypical, Hodgkin's-like cells for LMP-1 of EBV was noted in four cases; in the remaining case, this finding was equivocal. In situ hybridization for EBV-encoded RNA was positive in four of the five cases. Molecular studies by polymerase chain reaction (PCR) showed the presence of EBV in three of the five cases. PCR for detection of immunoglobulin heavy chain demonstrated identical monoclonal rearrangements in the original lymphoma and transformation in one case with available material. The CD4 lymphocyte count in each patient was less than 550/microL, indicating cellular dysfunction. Transformation of low-grade non-Hodgkin's lymphomas after fludarabine therapy might be associated with EBV and severe immunosuppression.

Hematologic disorders associated with deletions of chromosome 20q: a clinicopathologic study of 107 patients

To study the pathogenetic significance of acquired del(20q), bone marrow morphology and clinical histories of 107 patients with hematologic disorders and the del(20q) were studied. In 84 cases representing myelodysplastic syndromes (47), myeloproliferative disorders (31), acute myeloid leukemia (3), pure red blood cell aplasia (2), and angioimmunoblastic lymphadenopathy with dysproteinemia (AILD-like T-cell lymphoma (1), 20q- was the sole karyotypic abnormality. The breakpoints on chromosome 20 were not constant, and in 77% of cases, only a fraction of the studied metaphases had del(20q). In 23 cases, including myelodysplastic syndromes (13), myeloproliferative disorders (6), acute myeloid leukemia (2), and autoimmune disorders (2), 20q- occurred with other cytogenetic abnormalities, including del(5q), -7, +8, 13q deletion or translocation, and +21. Despite the diagnostic heterogeneity, the bone marrow morphologic abnormalities consistently involved the erythroid precursors and megakaryocytes. 20q- is a primary cytogenetic abnormality occurring in hematologic disorders unified morphologically by dysplasia in erythroid precursors and megakaryocytes. In conjunction with other studies of disorders involving del(20q) or genes on the long arm of chromosome 20, the findings suggest that del(20q) disproportionately affects a common megakaryocytic/RBC stem cell.

Extramedullary myeloid cell tumors in acute nonlymphocytic leukemia: a clinical review

PURPOSE

To discuss the predisposing risk factor for all forms of extramedullary leukemia (EML) and to review the clinical features, prognostic significance, and treatment strategies for primary EML and leukemia cutis (LC)/granulocytic sarcomas (GS) in the setting of acute nonlymphocytic leukemia (ANLL).

METHODS

A review of all reports published since 1965 related to all forms of extramedullary leukemia (LC, GS, gingival hypertrophy, and meningeal leukemia [ML]).

RESULTS

Several factors, including chromosomal abnormalities [t(8;21), inv(16)], cell-surface markers (CD56, CD2, CD4, CD7), French-American-British (FAB) subtype (M2, M4, M5), blast differentiation and maturation, patient nutritional status, age, cellular immune dysfunction, high presenting leukocyte count, and decreased blast Auer rods, have been associated with a higher incidence of EML. Of 154 published cases of primary EML identified, 71 (46%) were initially misdiagnosed. The addition of immunohistochemical stains can assist in preventing such misdiagnoses and should be included in all atypical lymphoma/carcinoma cases. Only one of the patients (3%) with primary EML did not progress to ANLL in the absence of chemotherapy. In contrast, 66% of patients who received chemotherapy for the primary EML never developed ANLL. The prognostic significance of EML at presentation and medullary relapse of ANLL is uncertain. Isolated extramedullary recurrence of ANLL always heralds bone marrow relapse and should be treated with reinduction chemotherapy. Close clinical follow-up observation is necessary to insure resolution of EML. Radiation therapy is an effective local treatment for resistant or symptomatic EML.

CONCLUSION

Many advances in diagnoses and treatment of EML have been made. Future investigations are needed to define the clinical significance of EML in patients with ANLL treated with modern chemotherapy or bone marrow transplantation.