Paxillin is a 68-kDa focal adhesion protein that is phosphorylated on tyrosine residues in fibroblasts in response to transformation by v-src, treatment with platelet-derived growth factor, or cross-linking of integrins. Paxillin has been shown to have binding sites for the SH3 domain of Src and the SH2 domain of Crk in vitro and to coprecipitate with two other focal adhesion proteins, vinculin and focal adhesion kinase (p125fak). After preliminary studies showed that paxillin was a substrate for the hematopoietic oncogene p210BCR/ABL, we investigated the role of this protein in hematopoietic cell transformation and signal transduction. A full-length length cDNA encoding human paxillin was cloned, revealing multiple protein domains, including four tandem LIM domains, a proline-rich domain containing a consensus SH3 binding site, and three potential Crk-SH2 binding sites. The paxillin gene was localized to chromosome 12q24 by fluorescence in situ hybridization analysis. A chicken paxillin cDNA was also cloned and is predicted to encode a protein approximately 90% identical to human paxil-lin. Paxillin coprecipitated with p210BCR/ABL and multiple other cellular proteins in myeloid cell lines, suggesting the formation of multimeric complexes. In normal hematopoietic cells and myeloid cell lines, tyrosine phosphorylation of paxillin and coprecipitation with other cellular proteins was rapidly and transiently induced by interleukin-3 and several other hematopoietic growth factors. The predicted structure of paxillin implicates this molecule in protein-protein interactions involved in signal transduction from growth factor receptors and the BCR/ABL oncogene fusion protein to the cytoskeleton.

Patients with t(8;21) and EML have a low CR rate and overall survival. An aggressive local and systemic induction therapy should be considered for this patient subset. The effectiveness of HDAC intensification in t(8;21) patients with EML is uncertain and warrants further study.

We prospectively assigned 289 consecutive children with acute lymphoblastic leukemia to receive one of two treatment programs on the basis of the presence or absence of certain risk factors at the time of diagnosis. Patients at high risk (62 percent of the total) had one or more of the following risk factors: age below two or above nine years, a white-cell count of 20,000 per cubic millimeter or more, the presence of T-cell immunologic markers, radiologic evidence of a mediastinal mass, and involvement of the central nervous system. Patients in both the standard-risk and high-risk groups were treated for two years, receiving intensive remission-induction therapy, central nervous system prophylaxis, weekly administration of high-dose asparaginase, and multiple-drug continuation therapy (which in the high-risk group included doxorubicin and a larger dose of prednisone). At a median follow-up of 35 months, the mean (+/- SE) event-free survival rates at four years among the patients in the standard-risk and high-risk groups were 86 +/- 4 percent and 71 +/- 4 percent, respectively (P = 0.003), for a total event-free survival of 77 +/- 3 percent. Within the high-risk group, the white-cell count at diagnosis and the sex of the patient were not significant prognostic indicators, but age below 12 months at diagnosis was associated with a very poor outcome. As compared with previous methods, this treatment program using four-drug induction and intensive asparaginase therapy has resulted in improved event-free survival in children with acute lymphoblastic leukemia.

No abstract

Polymerase chain reaction-based screening of childhood acute lymphoblastic leukemia (ALL) samples showed that a TEL/AML1 fusion transcript was detected in 27% of all cases, representing the most common known gene rearrangement in childhood cancer. The TEL/AML1 fusion results from a t(12;21)(p13;q22) chromosomal translocation, but was undetectable at the routine cytogenetic level. TEL/AML1-positive patients had exclusively B-lineage ALL, and most patients were between the ages of 2 and 9 years at diagnosis. Only 3/89 (3.4%) adult ALL patients were TEL/AML1-positive. Most importantly, TEL/AML1-positive children had a significantly lower rate of relapse compared with TEL/AML1-negative patients (0/22 v 16/54, P = .004). Co- immunoprecipitation experiments demonstrated that TEL/AML-1 formed homodimers in vitro, and heterodimerized with the normal TEL protein when the two proteins were expressed together. The elucidation of the precise mechanism of transformation by TEL/AML1 and the role of TEL/AML1 testing in the treatment of childhood ALL will require additional studies.

A new human megakaryocytic cell line (Dami) has been established from the blood of a patient with megakaryoblastic leukemia. The Dami cells grow primarily in suspension with a doubling time of 24 to 30 hours. By light and electron microscopy, the Dami cells range in size from 12 to 120 micron in diameter and have lobulated nuclei characteristic of megakaryocytes. At least 89% of the cells react with monoclonal antibodies against platelet glycoproteins (GP) Ib and IIB/IIIa, and glycophorin. The cells do not react with antibodies against lymphoid, monocyte, granulocyte, or macrophage antigens. Thirteen percent of the cells become polyploid, spontaneously achieving greater than 4N DNA ploidy levels. In response to phorbol myristate acetate (PMA), the proportion of cells with ploidy levels greater than 4N increased threefold and could be separated into discrete ploidy groups. PMA also increased the expression of GPIb, the GPIIb/GPIIIa complex,l and von Willebrand factor. Cytogenetic analysis revealed a human male hyperdiploid karyotype with a modal chromosome number of 54 to 64 and several consistent clonal chromosomal abnormalities. These included a partial deletion of chromosome 5 and a translocation involving chromosome 3. In contrast to other megakaryocytic cell lines in which only a small portion of the cells express the megakaryocytic phenotype, nearly all of the Dami cells express platelet glycoproteins. Thus, the Dami cells provide a superior model in which to study human megakaryocyte biochemistry and differentiation.

In the generation of the acutely transforming avian retrovirus E26, both myb and ets genes have been transduced, leading to the production of a Gag-Myb-Ets fusion protein. This co-occurrence of v-myb and v-ets oncogenes suggests that the two might have a functional relationship. To look for such a relationship, we tested the transcriptional activation activity of Myb alone or with coexpressed Ets-1 or Ets-2. Using the promoter of the v-Myb-inducible mim-1 gene as a target, we found that full-length c-Myb gene products were poor activators of transcription, while an oncogenic (truncated) form of this protein was a strong trans-activator. However, coexpression of Ets-2 with full-length or truncated forms of Myb greatly increased trans-activation. Coexpression of Ets-1, Fos, Jun, or Myc with Myb did not increase trans-activation of the mim-1 promoter. The ability of Myb and Ets-2 to transactivate was cooperative, since Ets-2 alone gave little or no activation. Bacterially synthesized Ets-2 protein was found to bind specifically to the mim-1 promoter, suggesting that it may be a target for both Myb and Ets proteins. Thus, Myb and Ets proteins can cooperate in transcriptional activation, and their co-occurrence in the E26 virus may reflect a functional relationship between these two oncoproteins. Truncated forms of Myb may have a reduced need for cooperating factors such as Ets-2, and this might constitute an important mechanism associated with oncogenic activation.

28S ribosomal RNA (rRNA) (2-4), suggesting that the absence of the human rRNA may be related to the loss of human chromosomes. It is not due to the absence of the human acrocentric chromosomes, which carry the structural genes for rRNA (5, 6), because Marshall et al. (4) found no human 28S rRNA in a large series of mousehuman hybrids that contained 2 to 11 human acrocentrics.The chromosome regions that carry the rRNA genes have been identified as the nucleolus organizer regions (NORs) (7), and these regions can be stained preferentially by the Ag-AS silver staining method (8). In human diploid cell cultures the Ag-AS method stains the short arm regions of most of the acrocentric chromosomes (9, 10). The NORs of the same human acrocentric chromosomes are not stained in a mouse-human hybrid that has lost some human chromosomes (11). There is no evidence to suggest that rRNA genes are deleted from the human acrocentrics in hybrid cells. Therefore the absence.of Ag-AS stain suggests that this method detects only chromosome regions that functioned as nucleolus organizers in the preceding interphase, and, by implication, produced rRNA.Somatic cell hybrids between either mouse peritoneal macrophages or mouse cells obtained from a teratocarcinoma and HT-1080 human fibrosarcoma cells retain human chromosomes and lose mouse chromosomes (12). If preferential chromosome elimination is closely correlated with preferential suppression of nucleolus organizer activity, these hybrids should express only human nucleolus organizer activity. This appears to be the case. METHODS BALB/c mouse peritoneal macrophages were obtained according to a modification of the procedure described by Cohn and Benson (13) and were fused with HT-1080-6TG human fibrosarcoma cells deficient in hypoxanthine phosphoribosyltransferase (EC 2.4.2.8) (12) in the presence of f3-propiolactone-inactivated Sendai virus at pH 8.0 (14). The fused cultures were maintained in hypoxanthine-aminopterin-thymidine (HAT) selective medium (15). Large colonies of hybrid cells were visible 3-4 weeks after fusion. The colonies were picked and, subsequently, grown. OTT6050 mouse teratocarcinoma cells were obtained from a solid teratocarcinoma of a strain 129 mouse (16,17) by cutting in small fragments in trypsin/EDTA, resuspending in Eagle's minimal essential medium (MEM), and filtering through sterile gauze. The teratocarcinoma cells were fused with HT-1080-6TG cells in the presence of f.-propiolactone-inactivated Sendai virus. Hybrid colonies were selected in hypoxanthine-aminopterin-thymidine medium.Hybrid cells were maintained in Eagle's medium supplemented with 10% fetal calf serum. Mitotic cells were shaken from the culture flasks and transferred to a centrifuge tube containing 0.1 ml of colcemid (10 Ag/ml) for every 10 ml of medium and the tubes were centrifuged immediately at 800 rpm in an IEC clinical centrifuge for 7 min. The cell pellet was resuspended in 75 mM KCI. After 10 min the suspension was centrifuged and the cells were fixed for an hour in freshly prepa...