SLP65 deficiency results in perpetual V(D)J recombinase activity in pre-B-lymphoblastic leukemia and B-cell lymphoma cells

Perpetual V(D)J recombinase activity involving multiple DNA double-strand break events in B-cell lineage leukemia and lymphoma cells may introduce secondary genetic aberrations leading towards malignant progression. Here, we investigated defective negative feedback signaling through the (pre-) B-cell receptor as a possible reason for deregulated V(D)J recombinase activity in B-cell malignancy. On studying 28 cases of pre-B-lymphoblastic leukemia and 27 B-cell lymphomas, expression of the (pre-) B-cell receptor-related linker molecule SLP65 (SH2 domain-containing lymphocyte protein of 65 kDa) was found to be defective in seven and five cases, respectively. SLP65 deficiency correlates with RAG1/2 expression and unremitting VH gene rearrangement activity. Reconstitution of SLP65 expression in SLP65-deficient leukemia and lymphoma cells results in downregulation of RAG1/2 expression and prevents both de novo VH-DJH rearrangements and secondary VH replacement. We conclude that iterative VH gene rearrangement represents a frequent feature in B-lymphoid malignancy, which can be attributed to SLP65 deficiency in many cases