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Early membrane events in polymorphonuclear cell (PMN) apoptosis: membrane blebbing and vesicle release, CD43 and CD16

P Nusbaum1, C Lainé, S Seveau

  • 1INSERM U 507 Hôpital Necker, Paris, France.

Biochemical Society Transactions
|May 26, 2004
PubMed

Insights

CD43 down-regulation during polymorphonuclear cell (PMN) apoptosis is not due to cell blebbing or vesicle release. These membrane events, including CD43 shedding, occur independently.

Area of Science:

  • Immunology
  • Cell Biology
  • Biochemistry

Background:

  • CD43 (leukosialin) is a major sialoglycoprotein on leukocytes.
  • Down-regulation of CD43 expression occurs during polymorphonuclear cell (PMN) apoptosis.
  • The mechanism of CD43 down-regulation during PMN apoptosis remains unclear.

Purpose of the Study:

  • To investigate the mechanism of CD43 down-regulation during PMN apoptosis.
  • To determine if CD43 is released via bleb-derived membrane vesicles.
  • To elucidate the relationship between CD43 down-regulation and other apoptotic membrane events.

Main Methods:

  • PMN apoptosis was induced by synchronization at 15°C followed by incubation at 37°C.
  • Membrane blebbing and vesicle release were observed using microscopy and quantified by flow cytometry.
  • Inhibitors of caspases, protein kinase C (PKC), and myosin light chain kinase (MLCK) were used.
  • CD43/CD16 expression, phosphatidylserine externalization (annexin V binding), and CD43 localization were analyzed.

Main Results:

  • Membrane blebbing, vesicle release, CD43/CD16 down-regulation, and phosphatidylserine externalization occurred concurrently.
  • Inhibiting caspases or PKC blocked annexin V binding but not CD43 down-regulation or vesicle release.
  • MLCK inhibition prevented blebbing and vesicle release but did not affect CD43 down-regulation.
  • Electron microscopy showed CD43 poorly expressed on blebs and concentrated at bleb necks.

Conclusions:

  • CD43 down-regulation during PMN apoptosis is not caused by cell blebbing or release of bleb-derived vesicles.
  • Cell blebbing, phospholipid 'flip-flop', and CD43/CD16 down-regulation are independent membrane events during PMN apoptosis.
  • The observed down-regulation of CD43 is not a consequence of proteolysis or internalization.

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