title: Leukotoxin (Leukothera®) targets active leukocyte function antigen-1 (LFA-1) protein and triggers a lysosomal mediated cell death pathway.
abstract: Leukotoxin (LtxA) is a protein toxin that is secreted from the oral bacterium, Aggregatibacter actinomycetemcomitans. LtxA targets specifically the β(2) integrin, leukocyte function antigen-1 (LFA-1) on white blood cells (WBCs) and causes cell death. LtxA preferentially targets activated WBCs and is being developed as a therapeutic agent for the treatment of WBC diseases such as hematologic malignancies and autoimmune/inflammatory diseases. However, the mechanism by which interaction between LtxA and LFA-1 results in cell death is not well understood. Furthermore, how LtxA preferentially recognizes activated WBCs is not known. We show here that LtxA interacts specifically with LFA-1 in the active (exposed) conformation. In THP-1 monocytes, LtxA caused rapid activation of caspases, but LtxA could overcome the inhibition of caspases and still intoxicate. In contrast, inhibiting the vesicular trafficking pathway or cathepsin D release from the lysosome resulted in significant inhibition of LtxA-mediated cytotoxicity, indicating a more potent, lysosomal mediated cell death pathway. LtxA caused rapid disruption of the lysosomal membrane and release of lysosomal contents into the cytosol. Binding of LtxA to LFA-1 resulted in the internalization of both LtxA and LFA-1, with LtxA localizing specifically to the lysosomal compartment. To our knowledge, LtxA represents the first bacterial toxin shown to localize to the lysosome where it induces rapid cell death.
authors.affiliation: Department of Oral Biology, New Jersey Dental School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103.
authors.forename: Kristina M
authors.initials: KM
authors.lastname: DiFranco
authors.affiliation: Department of Oral Biology, New Jersey Dental School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103.
authors.forename: Anukriti
authors.initials: A
authors.lastname: Gupta
authors.affiliation: Department of Oral Biology, New Jersey Dental School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103.
authors.forename: Lindsey E
authors.initials: LE
authors.lastname: Galusha
authors.affiliation: Department of Oral Biology, New Jersey Dental School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103.
authors.forename: Jarelys
authors.initials: J
authors.lastname: Perez
authors.affiliation: Department of Oral Biology, New Jersey Dental School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103.
authors.forename: To-Vy K
authors.initials: TK
authors.lastname: Nguyen
authors.affiliation: Department of Oral Biology, New Jersey Dental School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103.
authors.forename: Camille D
authors.initials: CD
authors.lastname: Fineza
authors.affiliation: Department of Oral Biology, New Jersey Dental School, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07103; Actinobac Biomed, Inc., North Brunswick, New Jersey 08902. Electronic address: kachlasc@umdnj.edu.
authors.forename: Scott C
authors.initials: SC
authors.lastname: Kachlany
mesh_terms: D020169:Caspases / Q000378:metabolism; D016923:Cell Death / Q000187:drug effects; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D005098:Exotoxins / Q000494:pharmacology*; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007425:Intracellular Membranes / Q000378:metabolism*; D016169:Lymphocyte Function-Associated Antigen-1 / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D009000:Monocytes / Q000378:metabolism*
chemical_list: D005098:Exotoxins; D007166:Immunosuppressive Agents; D016169:Lymphocyte Function-Associated Antigen-1; C018579:leukotoxin; D020169:Caspases