Abstract
When some human plasma cell lines are cultured with concanavalin A, the original light chain is replaced with another light chain which results from secondary VJ recombination (light chain shifting). We examined various intracellular factors involved in the induction of light chain shifting. Light chain shifting can be induced upon treatment with agents with phosphatase inhibitory activity such as caffeine and okadaic acid. Although the plasma cells used express both RAG-1 and RAG-2, the expression level of these proteins was not affected by caffeine or okadaic acid. Transcription of the germ line locus, which correlates to the locus activation for rearrangement, is also not influenced by phosphatase inhibition. However, the amount of signal broken-ended DNA intermediates generated during V(D)J rearrangement was shown to increase upon caffeine or okadaic acid treatment. The inhibitory activity of caffeine on phosphatase was the same as okadaic acid. However, caffeine exhibited much higher activity for VJ coding joint formation than okadaic acid. Therefore, although phosphatase inhibition might act, in part, on a mechanism by which V(D)J recombinase activity is regulated within the human plasma cells, other factor(s) are probably also involved in the process.
Highlights
Immunoglobulin genes are assembled during B cell development through a series of site-specific recombination events collectively termed V(D)J recombination [1]
Induction of New Light Chain Production in the Plasma B Cell Line HB4C5 by Caffeine Stimulation—We previously found that concanavalin A (ConA) simulation can induce light chain replacement in the human plasma cell line HB4C5, which is known to secrete IgM reactive to the human histone H2B [22]
We have previously found that the light chain replacement from an original to a novel chain can be induced in some human plasma cells by ConA stimulation [12, 13]
Summary
Immunoglobulin genes are assembled during B cell development through a series of site-specific recombination events collectively termed V(D)J recombination [1]. We have shown that secondary VJ recombination can occur in some human plasma cell lines when stimulated with concanavalin A (ConA)1 [12, 13] We call this process light chain shifting [14]. V(D)J recombinase activity is determined by the regulated expression of RAG-1 and RAG-2 [3] These genes are expressed only when B cells rearrange the Ig heavy and light chain loci. Plus we have found that enhancement of RAG expression is not sufficient to induce secondary VJ rearrangement in light chain shiftinginducible human plasma cells [13, 14]. We found that the RAG gene products and the transcription of the germ line locus is not sufficient to carry out secondary VJ recombination in human plasma cells. The phosphatase inhibition induced the formation of signal broken-ended DNA intermediates in the cells, which is an initial step in the V(D)J recombination process
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