H4(D10S170), a gene frequently rearranged in papillary thyroid carcinoma, is fused to the platelet-derived growth factor receptor b gene in atypical chronic myeloid leukemia with t(5;10)(q33;q22)

The molecular cloning of the t(5;10)(q33; q22) associated with atypical chronic myeloid leukemia (CML) is reported. Fluorescence in situ hybridization (FISH), Southern blot, and reverse transcriptase– polymerase chain reaction analysis demonstrated that the translocation resulted in an H4/platelet-derived growth factor receptor bR (PDGFbR) fusion transcript that incorporated 5* sequences from H4 fused in frame to 3* PDGFbR sequences encoding the transmembrane, WW-like, and tyrosine kinase domains. FISH combined with immunophenotype analysis showed that t(5;10)(q33;q22) was present in CD131 and CD141 cells but was not observed in CD31 or CD191 cells. H4 has previously been implicated in pathogenesis of papillary thyroid carcinoma as a fusion partner of RET. The H4/RET fusion incorporates 101 amino acids of H4, predicted to encode a leucine zipper dimerization domain, whereas the H4/PDGFbR fusion incorporated an additional 267 amino acids of H4. Retroviral transduction of H4/PDGFbR, but not a kinaseinactive mutant, conferred factor-independent growth to Ba/F3 cells and caused a T-cell lymphoblastic lymphoma in a murine bone marrow transplantation assay of transformation. Mutational analysis showed that the amino-terminal H4 leucine zipper domain (amino acids 5593), as well as H4 amino acids 101 to 386, was required for efficient induction of factor-independent growth of Ba/F3 cells. Tryptophan-to-alanine substitutions in the PDGFbR WW-like domain at positions 566/593, or tyrosine-to-phenylalanine substitutions at PDGFbR positions 579/581 impaired factor-independent growth of Ba/F3 cells. H4/PDGFbR is an oncoprotein expressed in t(5;10)(q33;q22) atypical CML and requires dimerization motifs in the H4 moiety, as well as residues implicated in signal transduction by PDGFbR, for efficient induction of factorindependent growth of Ba/F3 cells. (Blood. 2001;97:3910-3918)