title: Lymphocyte-specific protein tyrosine kinase (Lck) interacts with CR6-interacting factor 1 (CRIF1) in mitochondria to repress oxidative phosphorylation.
abstract: BACKGROUND
  Many cancer cells exhibit reduced mitochondrial respiration as part of metabolic reprogramming to support tumor growth. Mitochondrial localization of several protein tyrosine kinases is linked to this characteristic metabolic shift in solid tumors, but remains largely unknown in blood cancer. Lymphocyte-specific protein tyrosine kinase (Lck) is a key T-cell kinase and widely implicated in blood malignancies. The purpose of our study is to determine whether and how Lck contributes to metabolic shift in T-cell leukemia through mitochondrial localization.
  
  
  METHODS
  We compared the human leukemic T-cell line Jurkat with its Lck-deficient derivative Jcam cell line. Differences in mitochondrial respiration were measured by the levels of mitochondrial membrane potential, oxygen consumption, and mitochondrial superoxide. Detailed mitochondrial structure was visualized by transmission electron microscopy. Lck localization was evaluated by subcellular fractionation and confocal microscopy. Proteomic analysis was performed to identify proteins co-precipitated with Lck in leukemic T-cells. Protein interaction was validated by biochemical co-precipitation and confocal microscopy, followed by in situ proximity ligation assay microscopy to confirm close-range (<16 nm) interaction.
  
  
  RESULTS
  Jurkat cells have abnormal mitochondrial structure and reduced levels of mitochondrial respiration, which is associated with the presence of mitochondrial Lck and lower levels of mitochondrion-encoded electron transport chain proteins. Proteomics identified CR6-interacting factor 1 (CRIF1) as the novel Lck-interacting protein. Lck association with CRIF1 in Jurkat mitochondria was confirmed biochemically and by microscopy, but did not lead to CRIF1 tyrosine phosphorylation. Consistent with the role of CRIF1 in functional mitoribosome, shRNA-mediated silencing of CRIF1 in Jcam resulted in mitochondrial dysfunction similar to that observed in Jurkat. Reduced interaction between CRIF1 and Tid1, another key component of intramitochondrial translational machinery, in Jurkat further supports the role of mitochondrial Lck as a negative regulator of CRIF1 through competitive binding.
  
  
  CONCLUSIONS
  This is the first report demonstrating the role of mitochondrial Lck in metabolic reprogramming of leukemic cells. Mechanistically, it is distinct from other reported mitochondrial protein tyrosine kinases. In a kinase-independent manner, mitochondrial Lck interferes with mitochondrial translational machinery through competitive binding to CRIF1. These findings may reveal novel approaches in cancer therapy by targeting cancer cell metabolism.
authors.affiliation: Department of Microbiology and Immunology, H. M. Bligh Cancer Research Laboratories, Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL, 60064, USA. shahrooz.vahedi@my.rfums.org.
authors.forename: Shahrooz
authors.initials: S
authors.lastname: Vahedi
authors.affiliation: Department of Microbiology and Immunology, H. M. Bligh Cancer Research Laboratories, Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL, 60064, USA. fuyu.chueh@rosalindfranklin.edu.
authors.forename: Fu-Yu
authors.initials: FY
authors.lastname: Chueh
authors.affiliation: Department of Microbiology and Immunology, H. M. Bligh Cancer Research Laboratories, Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL, 60064, USA. bala.chandran@rosalindfranklin.edu.
authors.forename: Bala
authors.initials: B
authors.lastname: Chandran
authors.affiliation: Department of Microbiology and Immunology, H. M. Bligh Cancer Research Laboratories, Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL, 60064, USA. chaolan.yu@rosalindfranklin.edu.|Department of Biomedical Sciences, College of Medicine, Chang Gung University, 259 Wenhua 1st Road, Taoyuan City, 33302, Taiwan, Republic of China. chaolan.yu@rosalindfranklin.edu.
authors.forename: Chao-Lan
authors.initials: CL
authors.lastname: Yu
mesh_terms: D018797:Cell Cycle Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D015458:Leukemia, T-Cell / Q000378:metabolism*; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000378:metabolism*; D053078:Membrane Potential, Mitochondrial; D008928:Mitochondria / Q000378:metabolism / Q000502:physiology*; D009687:Nuclear Proteins / Q000378:metabolism*; D010085:Oxidative Phosphorylation; D040901:Proteomics / Q000379:methods
chemical_list: D018797:Cell Cycle Proteins; C120664:DNAJA3 protein, human; C476586:GADD45GIP1 protein, human; D050956:HSP40 Heat-Shock Proteins; D009687:Nuclear Proteins; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck)