Bruton's Tyrosine Kinase and SLP-65 Regulate Pre-B Cell Differentiation and the Induction of Ig Light Chain Gene Rearrangement

• Published in: Journal of Immunology 2006-04, Vol.176 (8), p.4543-4552
• Main Authors: Kersseboom, Rogier, Ta, Van B. T, Zijlstra, A. J. Esther, Middendorp, Sabine, Jumaa, Hassan, Fokko van Loo, Pieter, Hendriks, Rudolf W
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing; Agammaglobulinaemia Tyrosine Kinase; Animals; B-Lymphocytes - cytology; B-Lymphocytes - drug effects; B-Lymphocytes - immunology; Base Sequence; Carrier Proteins - genetics; Carrier Proteins - immunology; Cell Differentiation; Cell Proliferation; Cell Survival; DNA, Complementary - genetics; Gene Rearrangement, B-Lymphocyte, Light Chain; Interleukin-7 - pharmacology; Mice; Mice, Inbred C57BL; Mice, Knockout; Mice, Transgenic; Phosphoproteins - deficiency; Phosphoproteins - genetics; Phosphoproteins - immunology; Protein-Tyrosine Kinases - deficiency; Protein-Tyrosine Kinases - genetics; Protein-Tyrosine Kinases - immunology; Signal Transduction - drug effects; Transcription, Genetic
• ISSN: 0022-1767; 1550-6606; 1365-2567
• DOI: 10.4049/jimmunol.176.8.4543

Bruton's tyrosine kinase (Btk) and the adapter protein SLP-65 (Src homology 2 domain-containing leukocyte-specific phosphoprotein of 65 kDa) transmit precursor BCR (pre-BCR) signals that are essential for efficient developmental progression of large cycling into small resting pre-B cells. We show that Btk- and SLP-65-deficient pre-B cells have a specific defect in Ig lambda L chain germline transcription. In Btk/SLP-65 double-deficient pre-B cells, both kappa and lambda germline transcripts are severely reduced. Although these observations point to an important role for Btk and SLP-65 in the initiation of L chain gene rearrangement, the possibility remained that these signaling molecules are only required for termination of pre-B cell proliferation or for pre-B cell survival, whereby differentiation and L chain rearrangement is subsequently initiated in a Btk/SLP-65-independent fashion. Because transgenic expression of the antiapoptotic protein Bcl-2 did not rescue the developmental arrest of Btk/SLP-65 double-deficient pre-B cells, we conclude that defective L chain opening in Btk/SLP-65-deficient small resting pre-B cells is not due to their reduced survival. Next, we analyzed transgenic mice expressing the constitutively active Btk mutant E41K. The expression of E41K-Btk in Ig H chain-negative pro-B cells induced 1) surface marker changes that signify cellular differentiation, including down-regulation of surrogate L chain and up-regulation of CD2, CD25, and MHC class II; and 2) premature rearrangement and expression of kappa and lambda light chains. These findings demonstrate that Btk and SLP-65 transmit signals that induce cellular maturation and Ig L chain rearrangement independently of their role in termination of pre-B cell expansion.