Inhibition of cellular differentiation by the SCL/tal oncoprotein: transcriptional repression by an Id-like mechanism. Blood 85:465–471

In cases of T-cell acute lymphoblastic leukemia (T-ALL), the basic helix-loop-helix (bHLH) oncogene SCLltal undergoes frequent rearrangements activating ectopic expression. De-spite the compelling epidemiological association of SCLltal expression with l-ALL, no specific transforming function has been attributable to the protein product. However, investi-gators have recently demonstrated that forced overex-pression of SCL/tal can block monocytic differentiation of M1 murine myeloid leukemia cells. Thus, inappropriate ex-pression of wild-type SCLltal protein may in part account for the maturation arrest phenotype observed in T-ALL cells. In this study, ectopic expression of the SCLltal gene blocked EARRANGEMENTS of the SCL/tal locus occur in 15 % to 25 % of cases of T-cell acute lymphoblastic leukemia (T-ALL).I4 These rearrangements activate ectopi