title: Cross-talk between CD14 and complement receptor 3 promotes phagocytosis of mycobacteria: regulation by phosphatidylinositol 3-kinase and cytohesin-1.
abstract: The glycosylphosphatidyl anchored molecule CD14 to the monocyte membrane plays a prominent role in innate immunity, and the paradigms for CD14 selective signaling are beginning to be elucidated. In this study, transfected human monocytic cell line THP-1 and Chinese hamster ovary (CHO) fibroblastic cells were used to examine phagocytosis of Mycobacterium bovis bacillus Calmette-Guerin (BCG). Flow cytometry was combined with molecular and biochemical approaches to demonstrate a dual mechanism for BCG internalization involving either CD14 alone or a CD14-regulated complement receptor (CR)3-dependent pathway. Phagocytosis by CD14-positive THP-1 cells was attenuated by phosphatidylinositol-3 inhibitors LY294002 and wortmannin and experiments using transfected CHO cells showed substantial accumulation of phosphatidylinositol-3,4,5-trisphosphate at the BCG attachment site in CHO cells expressing CD14 and TLR2 suggesting that bacteria bind to CD14 and use TLR2 to initiate a PI3K signaling pathway. Additional experiments using blocking Abs showed that anti-TLR2 Abs inhibit phagocytosis of BCG by THP-1 cells. Furthermore, knockdown of cytohesin-1, a PI3K-regulated adaptor molecule for beta(2) integrin activation, specifically abrogated CD14-regulated CR3 ingestion of BCG consistent with the observation of physical association between CR3 and cytohesin-1 in cells stimulated with mycobacterial surface components. These findings reveal that mycobacteria promote their uptake through a process of "inside-out" signaling involving CD14, TLR2, PI3K, and cytohesin-1. This converts low avidity CR3 into an active receptor leading to increased bacterial internalization.
authors.affiliation: Department of Medicine, University of British Columbia and Vancouver Coastal Health Research Institute, Vancouver, British Columbia, Canada.
authors.forename: Khalid
authors.initials: K
authors.lastname: Sendide
authors.forename: Neil E
authors.initials: NE
authors.lastname: Reiner
authors.forename: Jimmy S I
authors.initials: JS
authors.lastname: Lee
authors.forename: Sylvain
authors.initials: S
authors.lastname: Bourgoin
authors.forename: Amina
authors.initials: A
authors.lastname: Talal
authors.forename: Zakaria
authors.initials: Z
authors.lastname: Hmama
mesh_terms: D000818:Animals; D016466:CHO Cells; D015815:Cell Adhesion Molecules / Q000378:metabolism; D002460:Cell Line; D006224:Cricetinae; D020662:Guanine Nucleotide Exchange Factors; D006801:Humans; D007113:Immunity, Innate; D018950:Lipopolysaccharide Receptors / Q000276:immunology* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D009161:Mycobacterium / Q000276:immunology / Q000472:pathogenicity*; D010587:Phagocytosis; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D020239:Receptor Cross-Talk / Q000276:immunology*; D011956:Receptors, Cell Surface / Q000378:metabolism; D011951:Receptors, Complement / Q000276:immunology*; D015398:Signal Transduction; D051195:Toll-Like Receptor 2; D051193:Toll-Like Receptors
chemical_list: D015815:Cell Adhesion Molecules; D020662:Guanine Nucleotide Exchange Factors; D018950:Lipopolysaccharide Receptors; D008562:Membrane Glycoproteins; D018129:Phosphatidylinositol Phosphates; D011956:Receptors, Cell Surface; D011951:Receptors, Complement; C495342:TLR2 protein, human; D051195:Toll-Like Receptor 2; D051193:Toll-Like Receptors; C100723:cytohesin-1; C060974:phosphatidylinositol 3,4,5-triphosphate; D019869:Phosphatidylinositol 3-Kinases