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PAX5/TEL Causes down Regulation of CD19 and TGFbeta Resistance in PreBI Cells.
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| Zeitschriftentitel: | Blood |
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| Personen und Körperschaften: | , , , , , |
| In: | Blood, 108, 2006, 11, S. 1416-1416 |
| Format: | E-Article |
| Sprache: | Englisch |
| veröffentlicht: |
American Society of Hematology
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| Schlagwörter: |
| Zusammenfassung: | <jats:title>Abstract</jats:title> <jats:p>The PAX5/TEL chimeric gene was cloned from the translocation t(9;12)(q11;p13) in an ALL patient. Recent data indicate that the PAX5/TEL fusion defines the cytogenetic entity dic(9;12)(p13;p13), which accounts for about 1% of childhood ALL, almost exclusively B-progenitor ALL.</jats:p> <jats:p>PAX5/TEL is likely to be an aberrant transcription factor, resulting from joining the 5′ region of PAX5 (a transcription factor essential for B cell development) to the 3′ region of TEL/ETV6, containing the Ets-family DNA binding domain.</jats:p> <jats:p>We have cloned the FLAG-full length chimeric PAX5/TEL cDNA in the retroviral vector pMSCV-IRES-GFP (MigR1) to transduce target cells. We have demonstrated a specific nuclear localization of the chimeric protein in NIH3T3 by immunofluorescence analysis. Moreover, we observed a PAX5/TEL dependent decrease of the cellular growth rate in IL-3 dependent murine proB Ba/F3 cells. We further investigated the function of the PAX5/TEL chimeric protein as a potential oncoprotein in murine preBI cells, as a more physiological model.</jats:p> <jats:p>Murine PAX5 −/− preBI cells and wild type preBI cells were purified as B220+/c-KIT+ cells from mouse fetal liver and they were cultured on OP9 and DL1-OP9 stroma cells in presence of IL-7. The OP9 stroma supports B cell proliferation and survival; the DL1-OP9 stroma expresses Delta-like1, one of the Notch ligands, and it’s important to support T cell development. Both PAX5 −/− preBI cells and wild type preBI cells were transduced with the retroviral construct pMSCV-PAX5/TEL-IRES-GFP to analyze cell proliferation, differentiation and growth-dependence on IL-7. Wild type preBI cells expressing PAX5/TEL showed down modulation of CD19 when cultured on OP9 stroma in presence of IL-7; an inverse correlation was observed between the levels of expression of GFP and of CD19. The down modulation of CD19 can be involved in driving the preBI cell into differentiation block. A possible explanation of CD19 repression can rely on a potential competition between PAX5/TEL and endogenous PAX5 to bind PAX5 consensus region on DNA.</jats:p> <jats:p>On OP9 stroma, PAX5/TEL preBI cells are resistant to TGFbeta anti-proliferative and apoptotic effects, with a three-fold increased growth rate than control cells. Although the specific mechanism of PAX5/TEL disruption of TGFbeta signalling pathway remains to be investigated, we propose the TGFbeta resistance by PAX5/TEL as a way to evade the immunosurveillance. PAX5/TEL-preBI cells cultured on DL1-OP9 showed a different phenotype, with up-regulation of c-KIT and down-regulation of CD44.</jats:p> <jats:p>PAX5−/− preBI cells infected with PAX5TEL and grown on OP9 were CD19 negative even in the presence of PAX5TEL. On DL1-OP9 stroma, PAX5TEL cells were able to differentiate maintaining the developmental plasticity of PAX5 −/− preBI cells. These preliminary results indicate a role of PAX5/TEL as a transcription factor, potentially with a suppressor function, down regulating CD19 expression, thus suggesting a function on B cell differentiation. The chimera is able to interfere with TGFbeta pathway, inducing resistance and conferring an advantage in cell survival, evading the immunosurveillance.</jats:p> <jats:p>PAX5TEL do not replace PAX5 functions in PAX5−/− cells, it cannot activate PAX5 target genes as CD19, important for restoring B cell differentiation.</jats:p> <jats:p>Further analyeis are needed to better evaluate the role of PAX5/TEL protein, both in vivo and in vitro models.</jats:p> |
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| Umfang: | 1416-1416 |
| ISSN: |
0006-4971
1528-0020 |
| DOI: | 10.1182/blood.v108.11.1416.1416 |