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Phosphatase 2A participates in interferon-gamma's induced upregulation of C1 inhibitor mRNA expression

G D Heda1, K J Kehoe, F Mahdi

  • 1Thrombosis Research Center, Temple University School of Medicine, Philadelphia, PA, USA.

Blood
|April 1, 1996
PubMed

Insights

Interferon-gamma (IFN-gamma) upregulates C1 inhibitor (C1 INH) mRNA transcription in HepG2 cells. This process requires phosphatase 2A activity to dephosphorylate a substrate, but phosphatase 2A does not directly stimulate C1 INH gene expression.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Immunology

Background:

  • C1 inhibitor (C1 INH) is crucial for regulating plasma kallikrein and complement system activation.
  • Interferon-gamma (IFN-gamma) is known to modulate immune responses, but its precise effects on C1 INH expression require elucidation.

Purpose of the Study:

  • To investigate the molecular mechanisms by which IFN-gamma regulates C1 inhibitor (C1 INH) mRNA expression in HepG2 cells.
  • To identify the role of protein phosphatases in IFN-gamma-mediated C1 INH gene regulation.

Main Methods:

  • HepG2 cells were treated with IFN-gamma, protein synthesis inhibitors (cycloheximide, anisomycin), transcription inhibitors (actinomycin D), and phosphatase inhibitors (okadaic acid, calyculin, cantharidin).
  • C1 INH mRNA and precursor (hnRNA) levels were analyzed using Northern blotting.
  • Phosphatase 2A activity was measured in response to IFN-gamma and C6 ceramide stimulation.

Main Results:

  • IFN-gamma treatment led to increased C1 INH mRNA precursor (hnRNA) levels, indicating transcriptional upregulation.
  • Inhibition of phosphatase 1 and 2A (using okadaic acid, calyculin, cantharidin) blocked IFN-gamma-induced C1 INH mRNA expression.
  • While C6 ceramide increased phosphatase 2A activity, it did not induce C1 INH mRNA expression, suggesting IFN-gamma acts through a distinct pathway.

Conclusions:

  • IFN-gamma induces the transcriptional upregulation of C1 inhibitor (C1 INH) mRNA in HepG2 cells.
  • Phosphatase 2A activity is essential for IFN-gamma to upregulate C1 INH transcription, likely by dephosphorylating a regulatory substrate.
  • Phosphatase 2A itself is not a direct stimulator of C1 INH gene expression.

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