| Sumario: | CD47 activation through the C-terminus of thrombospondin-1 or its derived peptides (4N1K and PKHB1) induce regulated cell death (RCD) in several types of cancer. Recently, it was demonstrated that PKHB1, the first serum-stable CD47 agonist peptide, induce caspase-independent, calcium-dependent RCD in CLL cells, even in those resistant to conventional therapy. Therefore, the objective of the present work was to study the PKHB1-induced cell death mechanism in other types of leukemia. To that end, cell death induction was evaluated by flow cytometry, analyzing phosphatidilserine exposure (Ann-V) and plasma membrane permeability (PI), as well as caspase dependance (inhibitor Q-VD-OPH) or calcium dependance (BAPTA, calcium chelator). The results show that PKHB1 is a better inductor of cell death, compared to 4N1K, and it is selective to different types of leukemia (MEC-1, CEM, Junket, K562, HL-60, L5178Y-R), since it does not kill human peripheral mononuclear cells, nor cells derived from lymphoid organs of healthy mice. PKHB1-induced killing is caspase-independent in all cases.
Additionally, in CEM (human T lymphoblasts of acute lymphocytic leukemia, the principal type of childhood cancer) and L5178Y-R (murine T lymphoblasts) cells, death is not modulated by co-culture with chemoprotective bone marrow stromal cells; calcium chelation, however, inhibits PKHB1-induced cell death. Together, the results indicate that PKHB1 is effective in different types of leukemia, and induce caspase-independent, microenvironment-independent calcium-dependent RCD, in leukemic T lymphocytes. These results suggest that PKHB1-induced RCD could be conserved in different types of leukemia, and set the basis for further studies on murine models.
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