The human host defense peptide LL-37 induces apoptosis in a calpain- and apoptosis-inducing factor-dependent manner involving Bax activity.
LL-37 is a human cationic host defense peptide (antimicrobial peptide) belonging to the cathelicidin family of peptides. In this study, LL-37 was shown to kill Jurkat T leukemia cells via apoptosis. A loss of mitochondrial membrane potential, DNA fragmentation, and phosphatidylserine externalization were detected following LL-37 exposure, whereas apoptosis was independent of caspase family members. The specific apoptotic pathway induced by LL-37 was defined through the utilization of Jurkat cells modified to express antiapoptotic proteins, as well as cells deficient in various proteins associated with apoptosis. Of interest, both Bcl-2-overexpressing cells and cells deficient in Bax and Bak proteins displayed a significant reduction in LL-37-induced apoptosis. In addition, Jurkat cells modified in the Fas receptor-associated pathway showed no reduction in apoptosis when exposed to LL-37. Analysis of the involvement of apoptosis-inducing factor (AIF) in LL-37-mediated apoptosis revealed that AIF transferred from the mitochondria to the nucleus of cells exposed to LL-37, where it may lead to large-scale DNA fragmentation and chromatin condensation. AIF knockdown analysis resulted in LL-37-resistant cells. This suggests that AIF is mandatory in LL-37-mediated killing. Lastly, chelation or inhibition of Ca(2+) or calpains inhibited LL-37-mediated killing. Further analysis revealed that calpains were required for LL-37-mediated Bax translocation to mitochondria. Together, these data show that LL-37-induced apoptosis is mediated via the mitochondria-associated pathway in a caspase-independent and calpain- and AIF-dependent manner that involves Bax activation and translocation to mitochondria.
Department of Biochemistry, University of Alberta, Room 463, Medical Sciences Building, Edmonton, Alberta, Canada T6G 2H7. jmader@ualberta.ca
Jamie S
JS
Mader
Neeloffer
N
Mookherjee
Robert E W
RE
Hancock
R Chris
RC
Bleackley
D000595:Amino Acid Sequence; D023181:Antimicrobial Cationic Peptides / Q000138:chemical synthesis / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D051033:Apoptosis Inducing Factor / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000037:antagonists & inhibitors / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D020287:In Situ Nick-End Labeling; D019169:Jurkat Cells; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008928:Mitochondria / Q000187:drug effects / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009842:Oligopeptides / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D014162:Transfection; D051028:bcl-2-Associated X Protein / Q000378:metabolism*; D054804:Cathelicidins
D023181:Antimicrobial Cationic Peptides; D051033:Apoptosis Inducing Factor; C494826:BAX protein, human; D015853:Cysteine Proteinase Inhibitors; D009842:Oligopeptides; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D051028:bcl-2-Associated X Protein; D002154:Calpain; D053453:Caspase 9; D002118:Calcium; D054804:Cathelicidins