Myeloid sarcoma as the only manifestation in a rare mixed lineage leukemia-fusion-driven acute myeloid leukemia:A case report

BACKGROUND The mixed lineage leukemia(MLL)-eleven-nineteen lysine-rich leukemia(ELL)fusion gene is a rare occurrence among the various MLL fusion genes.We present the first case in which myeloid sarcoma(MS)was the only manifestation of adult MLL-ELL-positive acute myeloid leukemia(AML).CASE SUMMARY We report a case of a 33-year-old male patient who was admitted in June 2022 with a right occipital area mass measuring approximately 7 cm×8 cm.Blood work was normal.The patient underwent right occipital giant subscalp mass excision and incisional flap grafting.Immunohistochemistry was positive for myeloperoxidase,CD43 and CD45 and negative for CD3,CD20,CD34,and CD56.The bone marrow aspirate showed hypercellularity with 20%myeloblasts.Flow cytometry showed that myeloblasts accounted for 27.21%of the nucleated cells,which expressed CD33,CD38,and CD117.The karyotype was 46,XY,t(11,19)(q23;p13.1),-12,+mar/46,XY.Next-generation sequencing showed a fusion of MLL exon 7 to exon 2 of ELL.A diagnosis of MLL-ELL-positive AML(M2 subtype)with subcutaneous MS was made.CONCLUSION MLL-ELL-positive AML with MS is a rare clinical entity.Additional research is needed to elucidate the molecular mechanisms of the pathogenesis of MS.

Transcriptional addiction in mixed lineage leukemia: new avenues for target therapies

Mixed lineage leukemia(MLL)is an aggressive and refractory blood cancer that predominantly occurs in pediatric patients and is often associated with poor prognosis and dismal outcomes.Thus far,no effective target therapy for the treatment of MLL leukemia is available.MLL leukemia is caused by the rearrangement of MLL genes at 11q23,which generates various MLL chimeric proteins that promote leukemogenesis through transcriptional misregulation of MLL target genes.Biochemical studies on MLL chimeras have identified that the most common partners exist in the superelongation complex(SEC)and DOT1L complex,which activate or sustain MLL target gene expression through processive transcription elongation.The results of these studies indicate a transcription-related mechanism for MLL leukemogenesis and maintenance.In this study,we first review the history of MLL leukemia and its related clinical features.Then,we discuss the biological functions of MLL and MLL chimeras,significant cooperating events,and transcriptional addiction mechanisms in MLL leukemia with an emphasis on potential and rational therapy development.Collectively,we believe that targeting the transcriptional addiction mediated by SEC and the DOT1L complex will provide new avenues for target therapies in MLL leukemia and serve as a novel paradigm for targeting transcriptional addiction in other cancers.

PANoptosis-like cell death in ischemia/reperfusion injury of retinal neurons

PANoptosis is a newly identified type of regulated cell death that consists of pyroptosis,apoptosis,and nec roptosis,which simultaneously occur during the pathophysiological process of infectious and inflammatory diseases.Although our previous lite rature mining study suggested that PANoptosis might occur in neuronal ischemia/repe rfusion injury,little experimental research has been reported on the existence of PANoptosis.In this study,we used in vivo and in vitro retinal neuronal models of ischemia/repe rfusion injury to investigate whether PAN optosis-like cell death(simultaneous occurrence of pyroptosis,apo ptosis,and necroptosis)exists in retinal neuronal ischemia/repe rfusion injury.Our results showed that ischemia/repe rfusion injury induced changes in morphological features and protein levels that indicate PANoptosis-like cell death in retinal neurons both in vitro and in vivo.Ischemia/repe rfusion inju ry also significantly upregulated caspase-1,caspase-8,and NLRP3 expression,which are important components of the PANoptosome.These results indicate the existence of PANoptosis-like cell death in ischemia/reperfusion injury of retinal neurons and provide preliminary experimental evidence for future study of this new type of regulated cell death.

Ligustroflavone reduces necroptosis in rat brain after ischemic stroke through targeting RIPK1/RIPK3/MLKL

OBJECTIVE To explore the effect of ligustroflavone on ischemic brain injury in stroke rat and the under⁃lying mechanisms.METHODS A rat model of ischemic stroke was established by middle cerebral artery occlusion(MCAO).Administration of ligustroflavone(10,30,60 mg·kg-1,ig)15 min before ischemia,after which neurological deficit score and infarct volume were detected by longa score and TTC stain.The cell viability and necrosis rate of hypoxia-cultured PC12 cells(O2/N2/CO2,1:94:5,8 h)were evaluated by MTS and LDH release rate.Flow cytometry further verified the mortality rate of PC12 cells.Necroptosis-associated proteins(RIPK1,RIPK3 and MLKL/p-MLKL)were detected by Western blotting.The interaction between RIPK3 and RIPK1 or MLKL were confirmed by immunoprecipitation.Operating Environ⁃ment(MOE)program demonstrated the possible combination of ligustroflavone with RIPK1,RIPK3 and MLKL.RESULTS Ischemic injury(increase in neurological deficit score and infarct volume)and upregulation of necroptosis-associated proteins were showed in rat MCAO model.Administration of ligustroflavone(30 mg·kg^-1,ig)evidently improved neurological func⁃tion,reduced infarct volume,and decreased the levels of necroptosis-associated proteins except the RIPK1.Consistently,hypoxia-cultured PC12 cells caused cellular injury(LDH release and necroposis)concomitant with up-regulation of necroptosis-associated proteins,and these phenomena were blocked in the presence of ligustroflavone(25μmol·L^-1)except the elevated RIPK1 levels.Using the Molecular Operating Environment(MOE)program,we identified RIPK1,RIPK3,and MLKL as potential targets of ligustroflavone.Further studies showed that the interaction between RIPK3 and RIPK1 or MLKL was significantly enhanced,which was blocked in the presence of ligustroflavone.CONCLUSION Ligus⁃troflavone protects rat brain from ischemic injury,and its beneficial effect is related to the prevention of necroptosis through a mechanism involving targeting RIPK1,RIPK3,and/or MLKL.

MLKL forms cation channels

The mixed lineage kinase domain-like(MLKL)protein is a key factor in tumor necrosis factor-induced necroptosis.Recent studies on necroptosis execution revealed a commitment role of MLKL in membrane disruption.However,our knowledge of how MLKL functions on membrane remains very limited.Here we demonstrate that MLKL forms cation channels that are permeable preferential y to Mg2+rather than Ca2+in the presence of Na+and K+.Moreover,the N-terminal domain containing six helices(H1-H6)is sufficient to form channels.Using the substituted cysteine accessibility method,we further determine that helix H1,H2,H3,H5 and H6 are transmembrane segments,while H4 is located in the cytoplasm.Finally,MLKL-induced membrane depolarization and cell death exhibit a positive correlation to its channel activity.The Mg2+-preferred permeability and five transmembrane segment topology distinguish MLKL from previously identified Mg2+-permeable channels and thus establish MLKL as a novel class of cation channels.