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Ligand-independent thrombopoietin mutant receptor requires cell surface localization for endogenous activity

Caroline Marty1, Ronan Chaligné, Catherine Lacout

  • 1INSERM, U790, Villejuif 94805, France.

The Journal of Biological Chemistry
|March 6, 2009
PubMed

Insights

The thrombopoietin receptor (MPL) W515L mutation requires cell surface localization for JAK2 phosphorylation and signaling, crucial for myeloproliferative neoplasms like primary myelofibrosis.

Area of Science:

  • Hematology
  • Molecular Biology
  • Cell Biology

Background:

  • The activating W515L mutation in the thrombopoietin receptor (MPL) is implicated in myeloproliferative neoplasms.
  • MPL signaling is dependent on the JAK2 kinase.
  • Understanding MPL W515L signaling is critical for therapeutic development.

Purpose of the Study:

  • To investigate the intracellular signaling of the ligand-independent MPL(W515L) mutant.
  • To determine the role of receptor maturation and localization in MPL(W515L) signaling.
  • To elucidate the mechanism of JAK2 activation by MPL(W515L).

Main Methods:

  • Utilized endoplasmic reticulum (ER) retention KDEL sequence to trap MPL(W515L) in the ER/Golgi pathway.
  • Assessed cell growth, tumor formation in nude mice, and JAK2 phosphorylation.
  • Generated disulfide-bonded MPL(W515L) homodimers via S402C substitution.

Main Results:

  • MPL(W515L)-KDEL, retained in the ER/Golgi, failed to induce autonomous cell growth or tumor formation.
  • JAK2 co-immunoprecipitated with MPL(W515L)-KDEL but remained unphosphorylated.
  • Disulfide-bonded MPL(W515L-S402C)-KDEL localized to the cell surface, signaled constitutively, and induced JAK2 phosphorylation.

Conclusions:

  • The MPL(W515L)/JAK2 complex matures in an inactive conformation within the ER/Golgi.
  • Cell surface localization is essential for JAK2 phosphorylation and subsequent autonomous signaling.
  • These findings provide insights into the pathogenesis of MPL-driven myeloproliferative neoplasms.

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