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Chasing leukemia stem cells
Invited Speakers/ Experimental Hematology 42 (2014) S2–S11
S1019 - CHASING LEUKEMIA STEM CELLS Sean Armstrong Boston Children’s Hospital, Boston, Massachusetts, USA See addendum.
S1020 - LESSONS FROM MODELING CEBPA MUTANT ACUTE MYELOID LEUKEMIAS Claus Nerlov University of Edinburgh, Edinburgh, United Kingdom See addendum.
S7
S1021 - THE ZINC FINGER PROTEIN GFI1 MAINTAINS DEVELOPMENT AND PROGRESSION OF LYMPHOID LEUKEMIA BY BLOCKING THE ACTIVATION OF THE TUMOR SUPPRESSOR P53 Tarik M€or€oy 1 IRCM, Montreal, Quebec, Canada; 2l’Universite de Montreal, Montreal, Quebec, Canada Lymphoma and leukemia have an incidence of approximately 8% in North America and Europe. However, a large proportion of patients cannot be cured despite intensive therapy and new therapeutic approaches are needed. We found that the transcriptional repressor protein Growth factor independent-1 (Gfi1) is critical for the malignant transformation of lymphoid cells and that ablation of Gfi1 significantly delayed initiation and progression of lymphoid leukemia. This was observed using several independent experimental models using the carcinogen (N-ethyl-N-nitrosourea (ENU)) or non acute transforming retroviruses (MoMuLV) or overexpression of truncated Notch protein (Notch&DeltaCT) mimicking Notch mutations in human T-ALL. Most striking was that the ablation of Gfi1 in these tumor models led to the cure of mice without use of additional chemotherapy. In addition, we also observed that inhibition of Gfi1 could stop the expansion of leukemic cells from T-ALL patients grafted into immune-deficient mice. Biochemical analyses indicated that Gfi1 exerts its function by restricting the activity of the tumor suppressor p53 by limiting its methylation at K372 and thus its ability to activate pro-apoptotic targets genes such as Bax, Noxa (Pmaip1) and Puma (Bbc3). Using specific antibodies we can demonstrate that Gfi1 antagonizes Symd2 mediated methylation of p53 at K370 and also the Set9 mediated methylation at K372 in 293 cells. This effect of Gfi1 depends on an intact SNAG domain, i.e. could be mediated by LSD1. Similarly, in thymocytes from Gfi1 knockout mice or knockin mice that express a Gfi1 mutant with a disrupted SNAG domain, high levels of p53 methylated at K372 were found supporting the findings in 293 cells. Our data strongly suggest that Gfi1, p53 and LSD1 can form a tripartite complex, which enables the de-methylation of p53 at K370 and K372. Through this complex, Gfi1 is able to modulate p53 functions for instance in T-cells or myeloid cells. Since malignant transformation can induce stress and a DNA damage response, tumors with non-mutated p53 such as many lymphoid leukemias or lymphomas have to select for Gfi1 expression to counteract p53 induced cell death. In this situation, the inhibition or removal of Gfi1 leads to accelerated p53 mediated cell death and to tumor regression. We conclude that lymphoid leukemia are dependent upon Gfi1 and that Gfi1 may be suitable as a new therapeutic target to treat lymphoid malignancies, in particular by complementing the classical radio- and chemotherapy, which induce a DNA damage response in tumor cells.
S1019 - CHASING LEUKEMIA STEM CELLS Sean Armstrong Boston Children’s Hospital, Boston, Massachusetts, USA See addendum.
S1020 - LESSONS FROM MODELING CEBPA MUTANT ACUTE MYELOID LEUKEMIAS Claus Nerlov University of Edinburgh, Edinburgh, United Kingdom See addendum.
S7
S1021 - THE ZINC FINGER PROTEIN GFI1 MAINTAINS DEVELOPMENT AND PROGRESSION OF LYMPHOID LEUKEMIA BY BLOCKING THE ACTIVATION OF THE TUMOR SUPPRESSOR P53 Tarik M€or€oy 1 IRCM, Montreal, Quebec, Canada; 2l’Universite de Montreal, Montreal, Quebec, Canada Lymphoma and leukemia have an incidence of approximately 8% in North America and Europe. However, a large proportion of patients cannot be cured despite intensive therapy and new therapeutic approaches are needed. We found that the transcriptional repressor protein Growth factor independent-1 (Gfi1) is critical for the malignant transformation of lymphoid cells and that ablation of Gfi1 significantly delayed initiation and progression of lymphoid leukemia. This was observed using several independent experimental models using the carcinogen (N-ethyl-N-nitrosourea (ENU)) or non acute transforming retroviruses (MoMuLV) or overexpression of truncated Notch protein (Notch&DeltaCT) mimicking Notch mutations in human T-ALL. Most striking was that the ablation of Gfi1 in these tumor models led to the cure of mice without use of additional chemotherapy. In addition, we also observed that inhibition of Gfi1 could stop the expansion of leukemic cells from T-ALL patients grafted into immune-deficient mice. Biochemical analyses indicated that Gfi1 exerts its function by restricting the activity of the tumor suppressor p53 by limiting its methylation at K372 and thus its ability to activate pro-apoptotic targets genes such as Bax, Noxa (Pmaip1) and Puma (Bbc3). Using specific antibodies we can demonstrate that Gfi1 antagonizes Symd2 mediated methylation of p53 at K370 and also the Set9 mediated methylation at K372 in 293 cells. This effect of Gfi1 depends on an intact SNAG domain, i.e. could be mediated by LSD1. Similarly, in thymocytes from Gfi1 knockout mice or knockin mice that express a Gfi1 mutant with a disrupted SNAG domain, high levels of p53 methylated at K372 were found supporting the findings in 293 cells. Our data strongly suggest that Gfi1, p53 and LSD1 can form a tripartite complex, which enables the de-methylation of p53 at K370 and K372. Through this complex, Gfi1 is able to modulate p53 functions for instance in T-cells or myeloid cells. Since malignant transformation can induce stress and a DNA damage response, tumors with non-mutated p53 such as many lymphoid leukemias or lymphomas have to select for Gfi1 expression to counteract p53 induced cell death. In this situation, the inhibition or removal of Gfi1 leads to accelerated p53 mediated cell death and to tumor regression. We conclude that lymphoid leukemia are dependent upon Gfi1 and that Gfi1 may be suitable as a new therapeutic target to treat lymphoid malignancies, in particular by complementing the classical radio- and chemotherapy, which induce a DNA damage response in tumor cells.