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Structural and mechanistic features of protein O glycosylation linked to CD8+ T-cell apoptosis

Steven J Van Dyken1, Ryan S Green, Jamey D Marth

  • 1Howard Hughes Medical Institute and Department of Cellular and Molecular Medicine, University of California-San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0625, USA.

Molecular and Cellular Biology
|November 15, 2006
PubMed

Insights

The ST3Gal-I enzyme regulates CD8+ T-cell apoptosis, a crucial step in immune response contraction. Its absence triggers cell death independently of typical immune signals, revealing a novel apoptotic pathway.

Area of Science:

  • Immunology
  • Glycobiology
  • Cell Biology

Background:

  • CD8+ T-cell apoptosis is critical for immune response contraction but its triggers remain unclear.
  • ST3Gal-I (sialyltransferase) adds sialic acid to O-glycans, potentially mediating this apoptosis.
  • Understanding this process is key to controlling adaptive immunity.

Purpose of the Study:

  • To investigate the role of ST3Gal-I in CD8+ T-cell apoptosis during immune contraction.
  • To elucidate the signaling pathways initiated by ST3Gal-I deficiency.
  • To determine if this mechanism is relevant in vivo following infection or immunization.

Main Methods:

  • Studied apoptosis in ST3Gal-I deficient CD8+ T cells.
  • Analyzed caspase activation, DNA fragmentation, and phosphatidylserine externalization.
  • Assessed T-cell contraction in viral and bacterial infection models.
  • Investigated the role of CD43, core 2 O-glycosylation, Bcl-2, and Bim.

Main Results:

  • ST3Gal-I deficiency, not CD4+ T cells, induced CD8+ T-cell apoptosis without IL-2 or TCR signals.
  • Apoptosis involved caspase activation and DNA fragmentation.
  • ST3Gal-I function is post-transcriptionally regulated and essential for CD8+ T-cell contraction in vivo.
  • The mechanism bypasses Bcl-2 inhibition and involves an endogenous lectin-mediated pathway.

Conclusions:

  • ST3Gal-I is a key regulator of CD8+ T-cell apoptosis and immune contraction.
  • A novel, lectin-activated apoptotic pathway in CD8+ T cells is revealed.
  • This pathway is essential for resolving adaptive immune responses after antigen stimulation.

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