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Growth inhibition and apoptosis due to restoration of E2A activity in T cell acute lymphoblastic leukemia cells.

Park ST, Nolan GP, Sun XH - J. Exp. Med. (1999)

Bottom Line: The activation model suggests that Tal1 as heterodimers with the E2A transcription factor activates the expression of oncogenes.The inhibition model postulates that Tal1 interferes with the tumor-suppressing function of E2A.In the Jurkat T cell line, originally derived from a patient with T-ALL, Tal1 is complexed with E2A proteins and the transcriptional activity of E2A is very low.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, New York University Medical Center, New York 10016, USA.

ABSTRACT
Two models have been proposed for the molecular mechanism by which the Tal1 oncogene causes T cell acute lymphoblastic leukemia (T-ALL). The activation model suggests that Tal1 as heterodimers with the E2A transcription factor activates the expression of oncogenes. The inhibition model postulates that Tal1 interferes with the tumor-suppressing function of E2A. In the Jurkat T cell line, originally derived from a patient with T-ALL, Tal1 is complexed with E2A proteins and the transcriptional activity of E2A is very low. When E2A activity was restored by expressing an E2A-Tal1 fusion protein, E-T/2, the Jurkat cells underwent growth arrest and subsequently apoptosis, thus supporting the inhibition model and suggesting that E2A loss may contribute to leukemic progression.

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Treatment of infected  Jurkat/E cells with the caspase inhibitor, zVAD. (A) The growth of Jurkat/E cells infected with the vector  or E-T/2 virus. Cells were sorted for  GFP twice and plated in media containing 5% FCS without or with 1:500  vol/vol of DMSO or the same volume of zVAD (20 mM). On the indicated day after plating, cells were  counted as previously described. On  day 2, an equal volume of fresh medium containing the same concentration of zVAD or DMSO was added.  Data shown are representatives of  three separate experiments. (B) PI  staining. On day 4 after plating, the  cells cultured as in A were analyzed.  The percentage of apoptotic cells is  shown above the thin lines.
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Figure 5: Treatment of infected Jurkat/E cells with the caspase inhibitor, zVAD. (A) The growth of Jurkat/E cells infected with the vector or E-T/2 virus. Cells were sorted for GFP twice and plated in media containing 5% FCS without or with 1:500 vol/vol of DMSO or the same volume of zVAD (20 mM). On the indicated day after plating, cells were counted as previously described. On day 2, an equal volume of fresh medium containing the same concentration of zVAD or DMSO was added. Data shown are representatives of three separate experiments. (B) PI staining. On day 4 after plating, the cells cultured as in A were analyzed. The percentage of apoptotic cells is shown above the thin lines.

Mentions: These results raise the question of whether the growth retardation by E-T/2 is due to a primary apoptotic event or a cell cycle arrest that subsequently results in apoptosis. To address this question, we used the caspase inhibitor, zVAD-fluoromethylketone (zVAD; reference 32), to prevent apoptosis in E-T/2–expressing cells, and asked if the inhibitor could increase the growth rate of these cells. As shown in Fig. 5 A, addition of zVAD increased the growth of neither vector- nor E-T/2–infected cells over a period of 4 d (comparing cells treated with the zVAD inhibitor and with the DMSO vehicle). To determine if zVAD can prevent apoptosis in these cells, the vector- and E-T/2 infected cells were stained with PI on day 4. Indeed, the apoptotic population in E-T/2–infected cells was partially reduced by addition of zVAD (Fig. 5 B). As a control, Jurkat/E cells were cultured for 2 d in the absence of FCS to induce apoptosis. In the presence of zVAD, the apoptotic population also decreased dramatically. If the growth retardation in E-T/2–infected cells was due to enhanced apoptosis triggered by caspases, addition of zVAD would have been able to block the process and increase the growth rate. Therefore, our data suggests that the growth inhibition of these cells may not be the direct result of enhanced apoptosis mediated through the caspases, but rather may be due to an intrinsic poor ability of these cells to proliferate.


Growth inhibition and apoptosis due to restoration of E2A activity in T cell acute lymphoblastic leukemia cells.

Park ST, Nolan GP, Sun XH - J. Exp. Med. (1999)

Treatment of infected  Jurkat/E cells with the caspase inhibitor, zVAD. (A) The growth of Jurkat/E cells infected with the vector  or E-T/2 virus. Cells were sorted for  GFP twice and plated in media containing 5% FCS without or with 1:500  vol/vol of DMSO or the same volume of zVAD (20 mM). On the indicated day after plating, cells were  counted as previously described. On  day 2, an equal volume of fresh medium containing the same concentration of zVAD or DMSO was added.  Data shown are representatives of  three separate experiments. (B) PI  staining. On day 4 after plating, the  cells cultured as in A were analyzed.  The percentage of apoptotic cells is  shown above the thin lines.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2192921&req=5

Figure 5: Treatment of infected Jurkat/E cells with the caspase inhibitor, zVAD. (A) The growth of Jurkat/E cells infected with the vector or E-T/2 virus. Cells were sorted for GFP twice and plated in media containing 5% FCS without or with 1:500 vol/vol of DMSO or the same volume of zVAD (20 mM). On the indicated day after plating, cells were counted as previously described. On day 2, an equal volume of fresh medium containing the same concentration of zVAD or DMSO was added. Data shown are representatives of three separate experiments. (B) PI staining. On day 4 after plating, the cells cultured as in A were analyzed. The percentage of apoptotic cells is shown above the thin lines.
Mentions: These results raise the question of whether the growth retardation by E-T/2 is due to a primary apoptotic event or a cell cycle arrest that subsequently results in apoptosis. To address this question, we used the caspase inhibitor, zVAD-fluoromethylketone (zVAD; reference 32), to prevent apoptosis in E-T/2–expressing cells, and asked if the inhibitor could increase the growth rate of these cells. As shown in Fig. 5 A, addition of zVAD increased the growth of neither vector- nor E-T/2–infected cells over a period of 4 d (comparing cells treated with the zVAD inhibitor and with the DMSO vehicle). To determine if zVAD can prevent apoptosis in these cells, the vector- and E-T/2 infected cells were stained with PI on day 4. Indeed, the apoptotic population in E-T/2–infected cells was partially reduced by addition of zVAD (Fig. 5 B). As a control, Jurkat/E cells were cultured for 2 d in the absence of FCS to induce apoptosis. In the presence of zVAD, the apoptotic population also decreased dramatically. If the growth retardation in E-T/2–infected cells was due to enhanced apoptosis triggered by caspases, addition of zVAD would have been able to block the process and increase the growth rate. Therefore, our data suggests that the growth inhibition of these cells may not be the direct result of enhanced apoptosis mediated through the caspases, but rather may be due to an intrinsic poor ability of these cells to proliferate.

Bottom Line: The activation model suggests that Tal1 as heterodimers with the E2A transcription factor activates the expression of oncogenes.The inhibition model postulates that Tal1 interferes with the tumor-suppressing function of E2A.In the Jurkat T cell line, originally derived from a patient with T-ALL, Tal1 is complexed with E2A proteins and the transcriptional activity of E2A is very low.

View Article: PubMed Central - PubMed

Affiliation: Department of Cell Biology, New York University Medical Center, New York 10016, USA.

ABSTRACT
Two models have been proposed for the molecular mechanism by which the Tal1 oncogene causes T cell acute lymphoblastic leukemia (T-ALL). The activation model suggests that Tal1 as heterodimers with the E2A transcription factor activates the expression of oncogenes. The inhibition model postulates that Tal1 interferes with the tumor-suppressing function of E2A. In the Jurkat T cell line, originally derived from a patient with T-ALL, Tal1 is complexed with E2A proteins and the transcriptional activity of E2A is very low. When E2A activity was restored by expressing an E2A-Tal1 fusion protein, E-T/2, the Jurkat cells underwent growth arrest and subsequently apoptosis, thus supporting the inhibition model and suggesting that E2A loss may contribute to leukemic progression.

Show MeSH
Related in: MedlinePlus