Bruton's tyrosine kinase and SLP-65 regulate pre-B cell differentiation and the induction of Ig light chain gene rearrangement.
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.
Department of Immunology, Erasmus Medical Center, Rotterdam, The Netherlands.
Rogier
R
Kersseboom
Van B T
VB
Ta
A J Esther
AJ
Zijlstra
Sabine
S
Middendorp
Hassan
H
Jumaa
Pieter Fokko
PF
van Loo
Rudolf W
RW
Hendriks
D048868:Adaptor Proteins, Signal Transducing; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000818:Animals; D001402:B-Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000276:immunology*; D002454:Cell Differentiation; D049109:Cell Proliferation; D002470:Cell Survival; D018076:DNA, Complementary / Q000235:genetics; D015328:Gene Rearrangement, B-Lymphocyte, Light Chain; D015851:Interleukin-7 / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D010750:Phosphoproteins / Q000172:deficiency / Q000235:genetics / Q000276:immunology*; D011505:Protein-Tyrosine Kinases / Q000172:deficiency / Q000235:genetics / Q000276:immunology*; D015398:Signal Transduction / Q000187:drug effects; D014158:Transcription, Genetic
D048868:Adaptor Proteins, Signal Transducing; C113939:B cell linker protein; D002352:Carrier Proteins; D018076:DNA, Complementary; D015851:Interleukin-7; D010750:Phosphoproteins; D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625951:Btk protein, mouse