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Phosphorylation of Jak2 on Ser(523) inhibits Jak2-dependent leptin receptor signaling

Ryoko Ishida-Takahashi1, Felicia Rosario, Yusong Gong

  • 1Research Division, Joslin Diabetes Center, 1 Joslin Place, Boston, MA 02215, USA.

Molecular and Cellular Biology
|May 18, 2006
PubMed

Insights

Researchers discovered a new way the Jak2 protein is regulated. Phosphorylation at Serine 523 inhibits Jak2 activity, impacting cytokine signaling pathways and leptin receptor (LRb) function.

Area of Science:

  • Cellular signaling
  • Molecular biology
  • Biochemistry

Background:

  • Cytokine receptors, like the leptin receptor (LRb), lack intrinsic enzymatic activity.
  • They depend on associated Janus kinase (Jak) family tyrosine kinases for intracellular signal transduction.
  • Jak2 is the specific Jak kinase associated with LRb.

Purpose of the Study:

  • To elucidate the regulatory mechanisms of Jak2.
  • To identify how Jak2 mediates downstream signaling.
  • To understand the role of Jak2 phosphorylation in LRb signaling.

Main Methods:

  • Tandem mass spectrometry was used to identify phosphorylation sites on Jak2.
  • Site-directed mutagenesis was employed to study the functional impact of phosphorylation.
  • Experiments were conducted using HEK293 cells and mouse spleen tissue.

Main Results:

  • Serine 523 (Ser523) was identified as a novel site of Jak2 serine phosphorylation.
  • Ser523 phosphorylation was observed in intact cells and mouse spleen, independent of LRb-Jak2 activation.
  • Mutation of Ser523 enhanced and prolonged Jak2 signaling upon LRb activation, independent of Tyr570 inhibition.

Conclusions:

  • Phosphorylation of Jak2 at Ser523 represents a novel inhibitory mechanism regulating Jak2 activity.
  • This finding provides new insights into the regulation of Jak2-dependent cytokine signaling.
  • Understanding Ser523 phosphorylation is crucial for comprehending LRb-mediated cellular responses.

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