The pre-B-cell receptor (pre-BCR) is thought to signal transcriptional activation of the immunoglobulin light (L) chain gene locus, proceeding to its V-J rearrangement. The pre-BCR signaling pathway for this process is largely unknown but may involve the adaptor protein BASH (BLNK/SLP-65). Here we report that the pre-B leukemia cell lines established from affected BASH-deficient mice rearrange κL-chain gene locus and down-regulate pre-BCR upon PMA treatment or BASH reconstitution. Analyses with specific inhibitors revealed that activation of novel PKC (nPKC) and MEK, but not Ras, is necessary for the rearrangement. Accordingly, retroviral transduction of active PKCη, PKCε, or Raf-1, but not Ras, induced the κ gene rearrangement and expression in the pre-B-cell line. Tamoxifen-mediated BASH reconstitution resulted in the translocation of PKCη to the plasma membrane and κ chain expression. These data make evident that the Ras-independent BASH-nPKC-Raf-1 pathway of pre-BCR signaling induces the L-chain gene rearrangement and expression.
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