HYPOMETHYLATED STATUS, BUT NOT RAG-1, IS REQUIRED FOR T-CELL RECEPTOR-BETA-CHAIN GENE REARRANGEMENT IN ACUTE-LEUKEMIA CELLS

We studied the relation between the level of recombinase activating ge ne (RAG-1) and the methylation status of T-cell receptor (TCR)beta-cha in gene in TCR-beta rearrangement in acute leukemias, including 21 pat ients with B-precursor acute lymphoblastic leukemia (ALL) and 23 with acute myeloid leukemia (AML). The rearrangement of the TCR beta-chain gene in acute leukemia always occurs at the allele that contains hypom ethylated cytosine-cytosine-guanine-guanine (CCGG) sequences within ei ther the TCR-J beta 1 or TCR-J beta 1 regions. Moreover, all B-precurs or ALL patients with TCR-beta rearrangement had hypomethylated TCR-bet a with or without the presence of RAG-1 activity detectable by reverse transcript-polymerase chain reaction, whereas none of the AML patient s with TCR-beta rearrangement and hypomethylated TCR-beta had detectab le RAG-1 activity Some ALL patients had hypomethylated TCR-beta and RA G-1 activity without TCR-beta rearrangement, and most of them showed t (4;11) (q21;q23) or t(9;22) (q34;q11). These results indicate a correl ation between the hypomethylation status of the TCR-beta and its rearr angements, but some unknown blockage factor for this association exist s in B-precursor ALL patients with specific chromosomal translocations .