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Protein histidine phosphatase 1 negatively regulates CD4 T cells by inhibiting the K+ channel KCa3.1

Shekhar Srivastava1, Olga Zhdanova, Lie Di

  • 1Department of Pharmacology, New York University School of Medicine, New York, NY 10016, USA.

Proceedings of the National Academy of Sciences of the United States of America
|September 18, 2008
PubMed

Insights

Mammalian protein histidine phosphatase (PHPT-1) inhibits the KCa3.1 channel in T cells by dephosphorylation. Reduced PHPT-1 increases T cell activity and proliferation, revealing a new regulatory pathway in T cell receptor signaling.

Area of Science:

  • Immunology
  • Cell Biology
  • Biochemistry

Background:

  • The calcium-activated potassium channel KCa3.1 is crucial for T lymphocyte calcium signaling and maintaining membrane potential for calcium influx.
  • Nucleoside diphosphate kinase beta (NDPK-B), a histidine kinase, was previously identified as essential for KCa3.1 channel activation in human CD4 T lymphocytes.

Purpose of the Study:

  • To investigate the role of mammalian protein histidine phosphatase (PHPT-1) in regulating KCa3.1 channel activity in T lymphocytes.
  • To elucidate the mechanism by which PHPT-1 interacts with and modulates KCa3.1 channel function.
  • To determine the physiological significance of PHPT-1 in T cell receptor (TCR) signaling and T cell activation.

Main Methods:

  • Direct binding assays to confirm interaction between PHPT-1 and KCa3.1.
  • Site-directed mutagenesis to identify the dephosphorylation site (histidine 358) on KCa3.1.
  • Overexpression studies of wild-type and mutant PHPT-1 in human CD4 T cells.
  • siRNA-mediated knockdown of PHPT-1 expression in CD4 T cells.
  • Measurement of KCa3.1 channel activity, calcium (Ca2+) influx, and T cell proliferation following TCR activation.

Main Results:

  • PHPT-1 directly binds to KCa3.1 and inhibits its activity by dephosphorylating histidine 358.
  • Overexpression of wild-type PHPT-1, but not a phosphatase-dead mutant, suppressed KCa3.1 channel activity.
  • Knockdown of PHPT-1 using siRNA led to increased KCa3.1 channel activity, enhanced Ca2+ influx, and augmented proliferation in CD4 T cells upon TCR activation.

Conclusions:

  • Endogenous PHPT-1 acts as a negative regulator of KCa3.1 channel activity and TCR signaling in human CD4 T cells.
  • This study identifies a novel histidine phosphatase-mediated regulatory mechanism influencing T cell activation.
  • Histidine phosphorylation/dephosphorylation represents a previously unrecognized signaling pathway impacting biological processes in mammals, specifically in T lymphocyte function.

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