Thrombopoietin level in young patients is related to megakaryocyte frequency and platelet count.

PURPOSE: To examine the relationships among platelet counts, bone marrow megakaryocyte frequency, and circulating thrombopoietin (TPO) levels. PATIENTS AND METHODS: TPO levels in 17 children and one young adult with chronic or recurrent thrombocytopenia were measured by ELISA and megakaryocyte frequency was analyzed by light microscopy. Three groups of patients were studied: Group I patients had aplastic anemia and absent or decreased megakaryocytes; Group II patients had intermittent periods of chemotherapy-induced thrombocytopenia; and Group III patients had normal or increased megakaryocytes. Controls consisted of 77 healthy adults. RESULTS: Patients in Group I had markedly increased TPO levels compared to normal controls. Their levels were significantly different (p = 0.03) from those of patients in Group III. The latter had normal or only mildly increased TPO levels except for one patient with myelodysplastic syndrome. Patients in Group II had markedly elevated TPO levels. After their bone marrow and platelet counts recovered from chemotherapy, their TPO levels decreased. In all three groups, a transient increase in platelet count (e.g., after platelet transfusion or anti-D immune globulin therapy) was associated with a moderate decrease in TPO. CONCLUSIONS: From this study, three conclusions can be made: 1) TPO levels are inversely related to megakaryocyte frequency; 2) platelet counts have a modest influence on TPO level; and 3) TPO levels may have clinical utility in diagnosis and management and further our understanding of the pathobiology of the disorders that cause thrombocytopenia.

Nucleolar localization of the nucleophosmin-anaplastic lymphoma kinase is not required for malignant transformation.

The (2;5)(p23;q35) lymphoma-associated chromosomal translocation creates a novel fusion gene that incorporates parts of the anaplastic lymphoma kinase (ALK) receptor tyrosine kinase and nucleophosmin genes. We report here that the product of this fusion gene accumulates within the nucleoli of neoplastic cells, and that previous reports of a predominantly cytoplasmic localization for the protein represent a tissue-processing artifact. However, nucleolar accumulation of nucleophosmin-ALK may not be necessary for its oncogenic action, because an ALK protein expressed in a lymphoma carrying a variant (1;2) chromosomal translocation did not accumulate in nucleoli. Furthermore, an engineered hybrid TPR-ALK protein can transform rodent fibroblasts and produce lymphomas in mice while remaining confined to the cytoplasm. We propose that the transforming action of ALK may not be reliant on its nucleolar localization, a hypothesis that may have implications for studies of other proteins involved in oncogenesis that are relocalized after the creation of fusion genes.

Retrovirus-mediated gene transfer of NPM-ALK causes lymphoid malignancy in mice.

Approximately 5% to 10% of all non-Hodgkin's lymphomas contain a t(2;5)(p23;q35) chromosomal rearrangement, which we have previously shown results in the generation of the fusion protein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK). To assess the transforming potential of NPM-ALK in an animal model, we infected 5-fluorouracil-treated murine bone marrow using retroviral stocks and transplanted this infected marrow into lethally irradiated BALB/cByJ mice. Male mice were transplanted with bone marrow from female donors at 10 weeks of age, with 7 of the animals receiving marrow infected with a retroviral construct, pSR alphaMSVtkneo-NPM-ALK, that contains the human NPM-ALK cDNA, and 4 serving as a control group, receiving "empty" pSR alphaMSVtkneo-infected marrow. Whereas all mice in the control group were alive and well up to 11 months after transplantation, 4 of the 7 mice transplanted with marrow containing the NPM-ALK construct developed lymphoma within 4 to 6 months. Tumors arose in the mesenteric lymph nodes, with metastases to the lungs, kidneys, liver, spleen, and the paraspinal area. When cells from the tumors and bone marrow were transplanted into sublethally irradiated secondary recipients, 10 of these 13 mice developed tumors within 9 months. Immunoblot analysis of cell lysates using an ALK polyclonal antibody showed NPM-ALK expression in all tumors examined. Histologically, the tumors were composed of a uniform population of large immunoblastic cells with basophilic cytoplasm, centrally placed nuclei, and distinct nucleoli. Genotypic analysis showed that the tumors were B-lineage and clonal, with rearrangements of the Ig heavy- and kappa light-chain loci and no rearrangements of the T-cell receptor beta locus. Immunocytochemical studies confirmed the presence of IgM heavy chains and kappa light chains within the tumor cells. Thus, in this retroviral gene transfer model, NPM-ALK expression in mice causes B-lineage large-cell lymphoma, suggesting a direct causative role for this activated fusion tyrosine kinase in human lymphoma.

Papillary thyroid carcinoma: demographics, treatment, and outcome in eleven pediatric patients treated at a single institution.

We describe 11 cases (8 females, 3 males) of papillary thyroid carcinoma in children treated at St. Jude Children's Research Hospital over a 33-year period, and review the literature. Ages ranged from 7-25 years (median, 16 years). Six patients had primary papillary thyroid carcinoma. Five patients had secondary papillary thyroid carcinoma after treatment of Hodgkin's disease (n = 2), acute lymphoblastic leukemia (n = 2), and neuroblastoma (n = 1) with chemotherapy and cervical radiation. The typical presentation was either cervical lymphadenopathy or a thyroid mass of short duration. Treatment consisted of thyroidectomy, cervical lymph node dissection, and postoperative thyroid hormone replacement (n = 1), parathyroid reimplantation (n = 1), 131I ablation (n = 4), external-beam irradiation (n = 1), and chemotherapy with doxorubicin (n = 1) or carboplatin and topotecan (n = 1). Nine patients are alive without evidence of disease 3.0-22.4 years from diagnosis. One patient has persistent but stable disease 17.3 years after diagnosis. One patient relapsed with metastatic lung disease 0.3 years after the initial diagnosis. He continues to do well after a brief but unsustained complete radiographic remission of disease to combination chemotherapy with carboplatin and topotecan. Our review supports excellent long-term outcome for primary or secondary papillary thyroid carcinoma in pediatric patients although complications may require close follow-up in a multidisciplinary setting.

The gene encoding LERK-7 (EPLG7, Epl7), a ligand for the Eph-related receptor tyrosine kinases, maps to human chromosome 5 at band q21 and to mouse chromosome 17.

The eph-related receptors are the largest subfamily of receptor tyrosine kinases. Recently, we and others have identified seven different, but related, cDNAs encoding membrane-bound ligands for this family of receptors. One member, LERK-7, is attached to the cell membrane via glycosyl-phosphatidylinositol linkage and has been found to be a ligand for the eph-family receptors hek, elk, eck, and rek. Using PCR-based screening of human x rodent somatic cell hybrid DNAs, we have assigned the gene that encodes LERK-7 (EPLG7) to human chromosome 5. Fluorescence in situ hybridization to metaphase chromosome preparations using a genomic clone from the locus refined this localization to chromosome 5, band q21. In addition, Southern blot analysis of DNAs from interspecific backcross mice indicated that the mouse homologue Epl7 maps to a homologous region on chromosome 17.

cDNA cloning, tissue distribution, and chromosomal localization of myelodysplasia/myeloid leukemia factor 2 (MLF2).

A fusion gene between nucleophosmin (NPM) and myelodysplasia/myeloid leukemia factor 1 (MLF1) is formed by a recurrent t(3;5)(q25.1;q34) in myelodysplastic syndrome and acute myeloid leukemia. Here we report the identification of a novel gene, MLF2, which contains an open reading frame of 744 bp encoding a 248-amino-acid protein highly related to the previously identified MLF1 protein (63% similarity, 40% identity). In contrast to the tissue-restricted expression pattern of MLF1, the MLF2 messenger RNA is expressed ubiquitously. The MLF2 gene locus was mapped by fluorescence in situ hybridization to human chromosome 12p13, a chromosomal region frequently involved in translocations and deletions in acute leukemias of lymphoid or myeloid lineage. In a physical map of chromosome 12, MLF2 was found to reside on the yeast artificial chromosome clone 765b9. Southern blotting analysis of malignant cell DNAs prepared from a series of acute lymphoblastic leukemia cases with translocations involving chromosome arm 12p, as well as a group of acute myeloid leukemias with various cytogenetic abnormalities, failed to reveal MLF2 gene rearrangements.