May 26, 2004
Tracing the pre-B to immature B cell transition in human leukemia cells reveals a coordinated sequence of primary and secondary IGK gene rearrangement, IGK deletion and IGL gene rearrangement
By Florian Klein, Niklas Feldhahn, Jana L. Mooster
The BCR-ABL1 kinase expressed in acute lymphoblastic leukemia (ALL) drives malignant transformation of pre-B cells in humans and prevents further development. We studied whether inhibition of BCR-ABL1 kinase activity by the anti-leukemic drug STI571 can relieve this differentiation block: STI571-treatment of leukemia patients induced expression of the Ig light chain-associated transcription factors IRF4 and SPIB in parallel with upregulation of RAG1 and rearrangement of IGK and IGL genes. However, STI571-treated pre-B ALL cells expressed l- but almost no k-light chains. This was consistent with STI571-induced rearrangement of the k-deleting element (KDE), which can delete productively rearranged Vk -Jk joints. Amplifying short-lived DNA intermediates from double-strand breaks at recombination signal sequences within the IGK, KDE and IGL loci revealed a coordinated sequence of rearrangement events induced by STI571: Recombination of IGK gene segments is already initiated within one hour after STI571-treatment, followed by KDE-mediated deletion of Vk-Jk-joints six hours later and, ultimately, IGL gene rearrangement after 12 hours. Continued activity of the recombination machinery induced secondary IGK gene rearrangements, which shifted preferential usage of upstream located Jk- to downstream Jk- gene segments. Thus, inhibition of BCR-ABL1 in pre-B ALL cells i.) recapitulates early B cell development, ii.) directly shows that IGK, KDE and IGL genes are rearranged in sequential order and iii.) provides a model for Ig light chain gene regulation in the human.
Figure: Molecular analysis of recombination events within the IGK locus
