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The ubiquitin ligase NKLAM promotes apoptosis and suppression of cell growth

Paul A Willard1, Jacki Kornbluth2

  • 1Department of Pathology, Saint Louis University School of Medicine, St Louis, Missouri, USA.

The Journal of Biological Chemistry
|April 24, 2025
PubMed

Insights

Natural killer lytic-associated molecule (NKLAM) regulates immune responses by targeting c-Myc for degradation, inhibiting cell proliferation and inducing apoptosis. A key cysteine residue is crucial for its ligase activity.

Area of Science:

  • Immunology
  • Molecular Biology
  • Cell Biology

Background:

  • Natural killer lytic-associated molecule (NKLAM), also known as RNF19b, is an E3 ubiquitin ligase involved in immune regulation.
  • The precise mechanisms by which NKLAM influences cellular processes like proliferation and apoptosis are not fully understood.

Purpose of the Study:

  • To elucidate the role of a critical cysteine residue (C301) in NKLAM's ubiquitin ligase function.
  • To investigate the impact of NKLAM expression on cellular proliferation and apoptosis.
  • To determine the effect of NKLAM on the stability and degradation of the proto-oncogene c-Myc.

Main Methods:

  • Site-directed mutagenesis to create NKLAM mutants (C301S, C301A).
  • Inducible expression systems in HEK293 and K562 cells.
  • Cell proliferation assays (cell counting, metabolic activity).
  • Western blotting to assess c-Myc levels and proteasomal degradation assays.
  • Apoptosis assays (annexin-V staining, caspase activation).

Main Results:

  • Mutation of C301 to serine or alanine abolished NKLAM's ubiquitin ligase activity.
  • Wild-type NKLAM, but not the C301A mutant, inhibited cell proliferation and decreased c-Myc abundance.
  • NKLAM accelerated c-Myc proteasomal degradation, reducing its half-life.
  • Both wild-type NKLAM and the catalytically inactive C301S mutant induced apoptosis, suggesting a ligase-independent mechanism.

Conclusions:

  • NKLAM's ubiquitin ligase activity, dependent on C301, is essential for inhibiting proliferation via c-Myc degradation.
  • NKLAM can also induce apoptosis through a mechanism independent of its ligase activity.
  • NKLAM exhibits multifaceted roles in regulating cellular homeostasis, impacting both proliferation and cell death.
Keywords:
E3 ubiquitin ligaseNKLAMRBR ubiquitin ligaseRNF19bapoptosisc-Myccell deathcell metabolismnatural killer cells

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