Basic helix-loop-helix proteins E2A and HEB induce immature T-cell receptor rearrangements in nonlymphoid cells

T-cell receptor (TCR) gene rearrangements are mediated via V(D)J recombinat ion, which is strictly regulated during lymphoid differentiation, most prob ably through the action of specific transcription factors. Investigated was whether cotransfection of RAG1 and RAG2 genes in combination with lymphoid transcription factors can induce TCR gene rearrangements in nonlymphoid hu man cells. Transfection experiments showed that basic helix-loop-helix tran scription factors E2A and HEB induce rearrangements in the TCRD locus (D de lta2-D delta3 and V delta2-D delta3) and TCRG locus (psi V gamma7-J gamma2. 3 and V gamma8-J gamma2.3). Analysis of these rearrangements and their circ ular excision products revealed some peculiar characteristics. The V delta2 -D delta3 rearrangements were formed by direct coupling without intermediat e D delta2 gene segment usage, and most D delta2-D delta3 recombinations oc curred via direct coupling of the respective upstream and downstream recomb ination signal sequences (RSSs) with deletion of the D delta2 and D delta3 coding sequences. Subsequently, the E2A/HEB-induced TCR gene recombination patterns were compared with those in early thymocytes and acute lymphoblast ic leukemias of T- and B-lineage origin, and it was found that the TCR rear rangements in the transfectants were early (immature) and not necessarily T -lineage specific. Apparently, some parts of the TCRD (V delta2-D delta reg ion) and TCRG genes are accessible for recombination not only in T cells, b ut also in early B-cells and even in nonlymphoid cells if the appropriate t ranscription factors are present. The transfection system described here ap peared to be useful for studying the accessibility of immunoglobulin and TC R genes for V(D)J recombination, but might also be applied to study the ind uction of RSS-mediated chromosome aberrations. (Blood. 2001;98: 2456-2465) (C) 2001 by The American Society of Hematology.