Ligation of membrane IgM stimulates a novel c-Jun amino-terminal domain kinase activity in daudi human b cells

Xiaoli Li, Christopher C. Franklin, Andrew S. Kraft, Robert H. Carter

Research output: Contribution to journalArticlepeer-review


Stress-activated protein kinases (SAPK; also known as JNK for c-Jun N- terminal kinase) phosphorylate Ser63 and Ser73 in the amino-terminus of the c-Jun protein and potentiate its transcriptional activity. We have analysed phosphorylation of GST fusion proteins containing the c-Jun N-terminal domain by lysates of Daudi human B lymphoblastoid cells stimulated with medium or anti-IgM. Crosslinking membrane IgM (mIgM) results in an increase in phosphorylation of GST-c-Jun (5-89) in an antibody dose-dependent manner. The kinase activity specifically phosphorylates the c-Jun N-terminal domain since it does not phosphorylate GST or GST-JunB. The activity preferentially phosphorylates the substrate that contains the sites for in vivo phosphorylation by SAPK/JNK and requires the delta domain of c-Jun, which is also required for SAPK/JNK activity. However, the c-Jun N-terminal kinase activity induced by mIgM ligation is not precipitatable with anti-SAPK/JNK antibodies. In addition, unlike SAPK/JNKs, the mIgM-dependent c-Jun N- terminal kinase activity is not detectable in assays for renaturable kinase activity (in-gel assay) or in assays that test activities that bind to c-Jun (solid-phase assay). The increased phosphorylation of c-Jun N-terminal domain in response to mIgM ligation is unlikely to be due to mIgM-activated ERKs as it was not suppressed by a selective MEK inhibitor. Thus, the mIgM-induced activity is distinct from the known SAPK/JNKs and may represent a novel mechanism for c-Jun phosphorylation in response to mIgM engagement in human B cells.

Original languageEnglish (US)
Pages (from-to)409-418
Number of pages10
JournalMolecular Immunology
Issue number5
StatePublished - Apr 1997


  • B lymphocytes
  • C-Jun N- terminal kinase
  • Membrane antigen receptor
  • Signal transduction

ASJC Scopus subject areas

  • Immunology
  • Molecular Biology


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