title: Dynamic changes in Mcl-1 expression regulate macrophage viability or commitment to apoptosis during bacterial clearance.
abstract: Macrophages are critical effectors of bacterial clearance and must retain viability, despite exposure to toxic bacterial products, until key antimicrobial functions are performed. Subsequently, host-mediated macrophage apoptosis aids resolution of infection. The ability of macrophages to make this transition from resistance to susceptibility to apoptosis is important for effective host innate immune responses. We investigated the role of Mcl-1, an essential regulator of macrophage lifespan, in this switch from viability to apoptosis, using the model of pneumococcal-associated macrophage apoptosis. Upon exposure to pneumococci, macrophages initially upregulate Mcl-1 protein and maintain viability for up to 14 hours. Subsequently, macrophages reduce expression of full-length Mcl-1 and upregulate a 34-kDa isoform of Mcl-1 corresponding to a novel BH3-only splice variant, Mcl-1(Exon-1). Change in expression of Mcl-1 protein is associated with mitochondrial membrane permeabilization, which is characterized by loss of mitochondrial inner transmembrane potential and translocation of cytochrome c and apoptosis-inducing factor. Following pneumococcal infection, macrophages expressing full-length human Mcl-1 as a transgene exhibit a delay in apoptosis and in bacterial killing. Mcl-1 transgenic mice clear pneumococci from the lung less efficiently than nontransgenic mice. Dynamic changes in Mcl-1 expression determine macrophage viability as well as antibacterial host defense.
authors.affiliation: Division of Genomic Medicine, University of Sheffield, Sheffield, United Kingdom.
authors.forename: Helen M
authors.initials: HM
authors.lastname: Marriott
authors.forename: Colin D
authors.initials: CD
authors.lastname: Bingle
authors.forename: Robert C
authors.initials: RC
authors.lastname: Read
authors.forename: Karen E
authors.initials: KE
authors.lastname: Braley
authors.forename: Guido
authors.initials: G
authors.lastname: Kroemer
authors.forename: Paul G
authors.initials: PG
authors.lastname: Hellewell
authors.forename: Ruth W
authors.initials: RW
authors.lastname: Craig
authors.forename: Moira K B
authors.initials: MK
authors.lastname: Whyte
authors.forename: David H
authors.initials: DH
authors.lastname: Dockrell
mesh_terms: D017398:Alternative Splicing / Q000235:genetics / Q000502:physiology; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D002470:Cell Survival / Q000502:physiology; D005786:Gene Expression Regulation; D006801:Humans; D008264:Macrophages / Q000378:metabolism* / Q000382:microbiology / Q000473:pathology; D008564:Membrane Potentials; D051379:Mice; D008822:Mice, Transgenic; D008928:Mitochondria / Q000378:metabolism; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D011018:Pneumonia, Pneumococcal / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D020033:Protein Isoforms / Q000096:biosynthesis; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis* / Q000235:genetics; D013296:Streptococcus pneumoniae
chemical_list: C579094:Mcl1 protein, mouse; D064549:Myeloid Cell Leukemia Sequence 1 Protein; D009363:Neoplasm Proteins; D020033:Protein Isoforms; D019253:Proto-Oncogene Proteins c-bcl-2