title: Incorporation of podoplanin into HIV released from HEK-293T cells, but not PBMC, is required for efficient binding to the attachment factor CLEC-2.
abstract: BACKGROUND
  Platelets are associated with HIV in the blood of infected individuals and might modulate viral dissemination, particularly if the virus is directly transmitted into the bloodstream. The C-type lectin DC-SIGN and the novel HIV attachment factor CLEC-2 are expressed by platelets and facilitate HIV transmission from platelets to T-cells. Here, we studied the molecular mechanisms behind CLEC-2-mediated HIV-1 transmission.
  
  
  RESULTS
  Binding studies with soluble proteins indicated that CLEC-2, in contrast to DC-SIGN, does not recognize the viral envelope protein, but a cellular factor expressed on kidney-derived 293T cells. Subsequent analyses revealed that the cellular mucin-like membranous glycoprotein podoplanin, a CLEC-2 ligand, was expressed on 293T cells and incorporated into virions released from these cells. Knock-down of podoplanin in 293T cells by shRNA showed that virion incorporation of podoplanin was required for efficient CLEC-2-dependent HIV-1 interactions with cell lines and platelets. Flow cytometry revealed no evidence for podoplanin expression on viable T-cells and peripheral blood mononuclear cells (PBMC). Podoplanin was also not detected on HIV-1 infected T-cells. However, apoptotic bystander cells in HIV-1 infected cultures reacted with anti-podoplanin antibodies, and similar results were obtained upon induction of apoptosis in a cell line and in PBMCs suggesting an unexpected link between apoptosis and podoplanin expression. Despite the absence of detectable podoplanin expression, HIV-1 produced in PBMC was transmitted to T-cells in a CLEC-2-dependent manner, indicating that T-cells might express an as yet unidentified CLEC-2 ligand.
  
  
  CONCLUSIONS
  Virion incorporation of podoplanin mediates CLEC-2 interactions of HIV-1 derived from 293T cells, while incorporation of a different cellular factor seems to be responsible for CLEC-2-dependent capture of PBMC-derived viruses. Furthermore, evidence was obtained that podoplanin expression is connected to apoptosis, a finding that deserves further investigation.
authors.affiliation: Nikolaus-Fiebiger-Center for Molecular Medicine, University Hospital Erlangen, Erlangen, Germany.
authors.forename: Chawaree
authors.initials: C
authors.lastname: Chaipan
authors.forename: Imke
authors.initials: I
authors.lastname: Steffen
authors.forename: Theodros Solomon
authors.initials: TS
authors.lastname: Tsegaye
authors.forename: Stephanie
authors.initials: S
authors.lastname: Bertram
authors.forename: Ilona
authors.initials: I
authors.lastname: Glowacka
authors.forename: Yukinari
authors.initials: Y
authors.lastname: Kato
authors.forename: Jan
authors.initials: J
authors.lastname: Schmökel
authors.forename: Jan
authors.initials: J
authors.lastname: Münch
authors.forename: Graham
authors.initials: G
authors.lastname: Simmons
authors.forename: Rita
authors.initials: R
authors.lastname: Gerardy-Schahn
authors.forename: Stefan
authors.initials: S
authors.lastname: Pöhlmann
mesh_terms: D002478:Cells, Cultured; D004847:Epithelial Cells / Q000821:virology*; D015497:HIV-1 / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D037181:Lectins, C-Type / Q000378:metabolism*; D007963:Leukocytes, Mononuclear / Q000821:virology*; D008562:Membrane Glycoproteins / Q000378:metabolism*; D014771:Virion / Q000737:chemistry; D053585:Virus Attachment; D000098853:Podoplanin
chemical_list: D037181:Lectins, C-Type; D008562:Membrane Glycoproteins; C104778:CLEC2B protein, human; C117468:PDPN protein, human; D000098853:Podoplanin